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Multiple Choice Questions

1. A full-term female infant failed to gain weight and showed metabolic acidosis in the neonatal period. A physical examination at 6 months showed failure to thrive, hypotonia, small muscle mass, severe head lag, and a persistent acidosis (pH 7.0 to 7.2). Blood lactate, pyruvate, and alanine were greatly elevated. Treatment with thiamine did not alleviate the lactic acidosis. Which of the following enzymes is most likely deficient in this patient?

a) Alanine amino transferase

b) Phosphoenolpyruvate carboxy kinase

c) Pyruvate carboxylase

d) Pyruvate dehydrogenase

e) Pyruvate kinase

 The right answer is- d)

The symptoms are suggestive of Pyruvate dehydrogenase complex deficiency. Pyruvate dehydrogenase complex (PDC) deficiency (PDCD) is one of the most common neurodegenerative disorders associated with abnormal mitochondrial metabolism.

Pyruvate dehydrogenase, a multienzyme complex, catalyzes the conversion of pyruvate to acetyl co A. The major fate of Acetyl co A is oxidation in citric acid cycle, which is a chief metabolic cycle to derive energy from carbohydrates. Malfunction of this cycle deprives the body of energy. The impaired conversion of pyruvate to Acetyl co A leads to elevation of blood pyruvate, lactate and alanine. The persistent metabolic acidosis is due to accumulation of lactates in blood that results in nonspecific symptoms (e.g., severe lethargy, poor feeding, tachypnea), especially during times of illness, stress, or high carbohydrate intake. Similar symptoms though mild in nature can also be observed in Thiamine deficiency, as TPP is requires as a coenzyme for PDH complex. Since in the given case the patient is resistant to supplementation with thiamine, the deficiency of thiamine is ruled out.

Alanine transferase catalyzes the conversion of pyruvate to alanine (transamination). It cannot be the defect as alanine levels are also elevated.

 Phospho enol pyruvate carboxy kinase catalyzes the conversion of Oxaloacetate to phosphoenol pyruvate. The deficiency is rare.

Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate.

Pyruvate kinase catalyzes the conversion of phosphoenol pyruvate to pyruvate.

The clinical manifestations in the given case are only suggestive of PDH complex deficiency.

2. A 3- year-old female child whose growth rate has been in the lower 10th percentile over the last year presents with chronic, nonproductive cough and diarrhea with foul-smelling stools. She is diagnosed as having cystic fibrosis. For which of the following vitamins is this child most likely to be at risk of deficiency?

a)  Vitamin C

b) Vitamin B6

c) Folic acid

d) Retinol (vitamin A)

e) Riboflavin (vitamin B2)

The right answer is- d) – Cystic fibrosis, is an autosomal recessive disorder affecting approximately 1 in 2500 white individuals. It is caused due to defective chloride ion channels of exocrine glands and epithelial tissues involving pancreas, sweat glands, and mucous glands in the respiratory, digestive, and reproductive tracts. Affected patients usually have abnormal mucus secretion resulting in recurrent respiratory infections, gastrointestinal obstruction and pancreatic enzyme dysfunction.

The protein cystic fibrosis transmembrane conductance regulator (CFTR) is defective, leading to abnormal chloride transport. Because cystic fibrosis leads to pancreatic damage and diminution of the ability to secrete HCO3− and pancreatic digestive enzymes, as a result fat and protein are absorbed poorly. Retinol is a fat soluble vitamin that must be absorbed along with lipid micelles; hence the absorption of retinol is grossly affected.  The absorption of other fat-soluble vitamins E, D, and K is also decreased.

Vitamins C, B6, folic acid and riboflavin are water-soluble vitamins and their absorption is not significantly affected.

3. A 54-year-old male who was diagnosed with HIV (human immuno deficiency virus) infection 2 years back, is currently in the terminal stage. He is now cachectic and having a difficult time obtaining any caloric intake yet he refuses to take a naso gastric or gastric feeding tube. Since his muscle and organs are metabolically active, which of the following amino acids will produce both glucose and ketone bodies as an energy source?

a) Alanine

b) Tyrosine

c) Proline

d) Glycine

e) Leucine

The right answer is b) Tyrosine.

Tyrosine is the only amino acid in the given options that is both glucogenic as well as ketogenic. Upon metabolism tyrosine produce one molecule of fumarate and one molecule of acetoacetate. Fumarate is converted to Oxaloacetate (through intermediate formation of malate) which can be converted to glucose. Acetoacetate is cleaved to form 2 molecules of acetyl co A under the effect of Thiolase enzyme.  Since Acetyl co A is a precursor of ketone bodies, thus it represents the ketogenic component of Tyrosine.

Alanine can be transaminated to pyruvate (catalyzed by alanine transferase) which can be channeled towards the pathway of gluconeogenesis, thus it is purely glucogenic.

Proline upon metabolism produces Alpha ketoglutarate, a TCA cycle intermediate that can be converted to oxaloacetate and thus it is glucogenic.

Glycine is also purely glucogenic. Glycine is converted to serine that produces pyruvate by non oxidative deamination.

Leucine is purely ketogenic. Upon metabolism it produces acetoacetate and acetyl CoA, both are ketogenic fractions.

4. A 40 -year-old man presents with chest pain that radiates to his left jaw and shoulder. He is diagnosed with a myocardial infarct (heart attack) and is prescribed a statin medication. Statins are competitive inhibitors of HMG CoA reductase, which converts HMG Co A to which of the following?

a) Isopentenyl pyrophosphate

b) Mevalonate

c) Geranyl pyrophosphate

d) Farnesyl pyrophosphate

e) Cholesterol

The right answer is- b) Mevalonate.

The reaction catalyzed by HMG Co A reductase is the principal regulatory step in the pathway of cholesterol synthesis and is the site of action of the most effective class of cholesterol-lowering drugs, the HMG-CoA reductase inhibitors (statins). )

Isopentenyl pyrophosphate is formed from Mevalonate. Mevalonate is phosphorylated sequentially by ATP by three kinases, and after decarboxylation the active isoprenoid unit, Isopentenyl pyrophosphate (C5), is formed.

Isopentenyl diphosphate is isomerized by a shift of the double bond to form dimethylallyl pyrophosphate, then condensed with another molecule of Isopentenyl diphosphate to form the ten-carbon intermediate Geranyl pyrophosphate (C10).

A further condensation of Geranyl pyrophosphate (C10) with Isopentenyl pyrophosphate forms Farnesyl pyrophosphate (C15). Cholesterol is the final product of the pathway.

5. Which of the following compounds is the direct precursor for the heme nitrogen atoms?

a) Glucose

b) Glycine

c) Succinyl co A

d) Alanine

e) Methionine

The right answer is- b) Glycine.

Heme is synthesized in living cells by a pathway that requires Succinyl-CoA, derived from the citric acid cycle in mitochondria, and the amino acid glycine. The product of the condensation reaction between Succinyl-CoA and glycine is α-amino-β-ketoadipic acid, which is rapidly decarboxylated to form -δ-amino levulinate (ALA). Through a number of further steps Heme is synthesized.

Glucose does not have nitrogen in its structure to contribute towards heme formation, whereas alanine and methionine do possess amino groups but they do not contribute to Heme nitrogen.

6. A pregnant woman is able to transfer oxygen to her fetus because fetal hemoglobin has a greater affinity for oxygen than does adult hemoglobin. Why is the affinity of fetal hemoglobin for oxygen higher?

a) The tense form of hemoglobin is more prevalent in the circulation of the fetus.

b) There is less 2, 3-BPG in the fetal circulation as compared to maternal circulation.

c) Fetal hemoglobin binds 2, 3-BPG with fewer ionic bonds than the adult form.

d) The Bohr effect is enhanced in the fetus.

e) The oxygen-binding curve of fetal hemoglobin is shifted to the right.

The right answer is -c). The enhanced uptake of maternal oxygen by fetal Hb is due to less binding of 2, 3 BPG with fetal Hb.

It is not due to more prevalence of tense form of fetal hemoglobin in the circulation.

It is also not due to less 2, 3 BPG in the fetal circulation, the Bohr Effect is not enhanced in the fetus and the oxygen -binding curve of fetal Hb is also not shifted to the right.

In Hb A (adult Hb) when 2, 3-BPG binds to deoxyhemoglobin, it acts to stabilize the low oxygen affinity state (T state) of the oxygen carrier, exploiting the molecular symmetry and positive polarity by forming salt bridges with lysine and histidine residues in the four subunits of hemoglobin.

The R state, with oxygen bound to a heme group, has a different conformation and does not allow this interaction. By selectively binding to deoxyhemoglobin, 2, 3-BPG stabilizes the T state conformation, making it harder for oxygen to bind hemoglobin and more likely to be released to adjacent tissues.

Fetal hemoglobin (HbF) exhibits a low affinity for 2, 3-BPG, resulting in a higher binding affinity for oxygen. This increased oxygen-binding affinity relative to that of adult hemoglobin (HbA) is due to HbF’s having two α/γ dimers as opposed to the two α/β dimers of HbA. The positive histidine residues of HbA β-subunits that are essential for forming the 2, 3-BPG binding pocket are replaced by serine residues in HbF γ-subunits so 2, 3-BPG has difficulties in linking to the fetal hemoglobin, hence the affinity of fetal hemoglobin for O2 increases. That’s the way O2 flows from the mother to the fetus.

7. A 35-year-old female presents with severe dehydration and decreased urine output. Her blood urea nitrogen level is abnormally elevated because her kidneys are not able to excrete urea in the urine. In the production of urea, which of the following is an important intermediate?

a) Serine

b) Glutamate

c) Proline

d) Ornithine

e) Leucine

The right answer is-d) Ornithine

Urea is the end product of nitrogen/amino acid metabolism. Urea formation requires the participation of 6 amino acids which are aspartic acid, ornithine, citrulline, argino succinic acid, arginine and N-Acetyl glutamate. Out of these N -Acetyl glutamate is the only amino acid that acts as an allosteric activator of Carbamoyl phosphate synthase-1 enzyme, rest all participate in urea formation. Ornithine acts as a catalyst in the process of urea formation. Ornithine is a non standard amino acid, it is not incorporated in to tissue proteins but it participates in urea formation and polyamine synthesis.

Serine does not participate in urea formation. It is glucogenic, incorporated in to tissue proteins, required for synthesis of glycine, cysteine and sphingosine. Also participates in one carbon metabolism, forming O- glycosidic linkages and is present in at the active site of many enzymes.

Glutamate is a precursor of GABA, glutamine, glucogenic, a neurotransmitter and is incorporated in to tissue proteins. It does not participate in urea formation.

Proline also does not participate in urea formation; it is incorporated in to tissue proteins and is present at those places where kinks or bends are needed in the folding of the proteins since it is an imino acid. Collagen is rich in hydroxy proline (its hydroxylated form).

Leucine is a branched chain amino acid; it is purely ketogenic and has no role in urea formation.

8. Which of the following is a common compound shared by the TCA cycle and the urea cycle?

a) α-Keto glutarate

b) Argino succinic acid

c) Arginine

d) Fumarate

e) Aspartate

The right answer is- d) Fumarate.

Alpha ketoglutarate is an intermediate of TCA cycle; it has no connection with urea cycle.

Argino succinic acid is an intermediate of urea cycle and is formed by condensation of aspartic acid and Citrulline. It is not connected to TCA cycle, but upon breakdown it produces Arginine and fumarate. Fumarate is channeled towards TCA cycle. Fumarate is converted to malate and then to oxaloacetate through TCA cycle enzymes. Oxalo acetate is transaminated to form Aspartic acid that can be reutilized to form Argino succinic acid for continuation of urea cycle.

Aspartic acid is needed in urea formation but it is not an intermediate of TCA cycle.

Thus, Fumarate is the right answer.

9. Which enzyme often mal functions in diseases associated with the symptoms of high blood triglyceride levels and Steatorrhea?

a) Phospholipase D

b) Lipoprotein lipase

c) Thiokinase

d) Acetyl co A carboxylase

e) Pancreatic lipase

The right answer is- e) pancreatic lipase.

Steatorrhea occurs due to impaired digestion and absorption of lipids and other chief nutrients. It is characterized by passage of bulky stools and is often associated with deficiencies of fat soluble vitamins. Hypertriglyceridemia is a characteristic finding in Pancreatitis and there are several causes of Acute and chronic pancreatitis. In pancreatic disorders, pancreatic lipase deficiency results in impaired digestion of lipids as well as other nutrients causing Steatorrhea.

Phospholipase D enzyme is required for removal of nitrogenous base from phospholipid. It cannot cause the symptoms of high blood triglyceride levels and Steatorrhea.

Lipoprotein lipase is an enzyme for the degradation of triglacylglycerols present in chylomicrons and VLDL. Impaired activity can cause increase in serum triacylglycerol levels but Steatorrhea is unlikely to happen.

Thiokinase is the first enzyme of beta oxidation of fatty acids. It is required for the conversion of free fatty acid to fatty acyl co A (activation of fatty acid); it is also called Acyl Co A synthetase. This enzyme has nothing to do with lipid digestion or absorption and is not involved in the synthesis or degradation of triacylglycerols.

Acetyl co A carboxylase is an enzyme of fatty acid synthesis. It catalyzes the first step of conversion of acetyl co A to malonyl co A. It is the rate limiting step of de no fatty acid synthesis, malfunctioning of this enzyme cannot cause increase in TGs or Steatorrhea.

Thus the right answer is pancreatic lipase.

10. An infant is born with a high forehead, abnormal eye folds, and deformed ear lobes. He shows little muscle tone and movement. After multiple tests, he is diagnosed with Zellweger syndrome, a disorder caused by malformation of peroxisomes.
Which of the following is expected to be high in concentration in brain tissue of the affected individual?

a) Ketone bodies

b) Lactate

c) Cholesterol

d) Very long chain fatty acids

e) Glucose

The right answer is d), “Very long chain fatty acids”. Very long chain fatty acids are first trimmed in the peroxisomes till the length of C16 or C18, then they are transported to mitochondria in the conventional way though carnitine shuttle to be oxidized completely by beta oxidation.

Zellweger syndrome, also called cerebrohepatorenal syndrome is a rare, congenital disorder (present at birth), characterized by the reduction or absence of Peroxisomes in the cells of the liver, kidneys, and brain. In Zellweger syndrome the Peroxisomal trimming is impaired, thus VLFA accumulate in brain and blood of affected patients.

The option ketone body is ruled out because the above said symptoms are not characteristic of ketosis.

Lactate is also ruled out because excess of lactate (lactic acidosis) is also not a congenital disorder; lactate accumulates either due to non utilization (as in liver disorders) or excessive production (as in anaerobic conditions).

Cholesterol excess, hypercholesterolemia is also not the right option; the symptoms are suggestive of a congenital disorder that has affected the brain and physical growth. There is no such clinical state associated with hypercholesterolemia and impaired mental development.

Hyperglycemia is also not the right choice. Hyperglycemia is never associated with malformation of peroxisomes.

Hence the right option is very long chain fatty acids. For further details of Zellweger syndrome follow the link

http://www.namrata.co/minor-pathways-of-fatty-acids-oxidation-a-quick-review/

11. After excessive drinking over an extended period of time while eating poorly, a middle-aged man is admitted to the hospital with “high output” heart failure. Which of the following enzymes is most likely inhibited?

a) Aconitase

b) Citrate synthase

c) Isocitrate dehydrogenase

d) α-Ketoglutarate dehydrogenase

e) Succinate thiokinase

The right answer is d) – Alpha ketoglutarate dehydrogenase deficiency.

The patient is most probably suffering from cardiac beriberi. The criteria for diagnosing cardiac beriberi is- 1)  Signs of heart failure 2) signs of neuropathies 3) history of alcoholism or poor nutritional history, 4)exclusion of other signs of heart failure, 5) low red cell Transketolase activity 6) Response by thiamine administration.

The above said patient is a known alcoholic, mal nourished and has heart failure .The probable diagnosis is Thiamine deficiency, which can be confirmed by Erythrocyte Transketolase activity. Thiamine is required as a coenzyme for Pyruvate dehydrogenase complex, alpha ketoglutarate dehydrogenase complex, transketolase and alpha keto acid dehydrogenase complex.

Out of all the given options only alpha ketoglutarate dehydrogenase is the only enzyme which is Thiamine dependent and that could possibly be inhibited in beri-beri.

Aconitase is iron dependent enzyme of TCA cycle. All the enzymes enlisted are though enzymes of TCA cycle, but the deficiencies of Aconitase, citrate synthase, isocitrate dehydrogenase and succinate thiokinase are unknown. Alpha ketoglutarate dehydrogenases deficiency is unknown but its impaired activity is observed in thiamine deficiency. TCA cycle enzyme deficiencies are incompatible with life proving that TCA cycle is vital to life.

12. A 16-month-old girl was found to have ingested approximately 30 mL of an acetonitrile-based cosmetic nail remover when she vomited 15 minutes post ingestion. The poison control center was contacted, but no treatment was recommended because it was confused with an acetone-based nail polish remover. The child was put to bed at her normal time, which was 2 hours post ingestion. Respiratory distress developed sometime after the child was put to bed, and she was found dead the next morning.

Inhibition of which of the following enzymes was the most likely cause of this child’s death?

a) Cytochrome c reductase

b) Cytochrome oxidase

c) Coenzyme Q reductase

d) NADH dehydrogenase

e) Succinate dehydrogenase

 The right answer is-b) – Cytochrome oxidase.

 Acetonitrile is used mainly as a solvent. It is the chemical compound with the formula CH3CN. Acetonitrile has only a modest toxicity in small doses. It can be metabolized to produce hydrogen cyanide, which is the source of the observed toxic effects. Generally the onset of toxic effects is delayed, due to the time required for the body to metabolize acetonitrile to cyanide (generally about 2–12 hours). It has been used in formulations for nail polish remover, despite its low but significant toxicity. Acetone and ethyl acetate are often preferred as safer for domestic use, and acetonitrile has been banned in cosmetic products in the European Economic Area since March 2000.

Cyanide released from the metabolism of acetonitrile, is an inhibitor of Cytochrome oxidase. Electron flow in cytochrome c oxidase can be blocked by hydrogen sulphide (H2S), cyanide (CN-), azide (N3 -), and carbon monoxide (CO). Cyanide and azide react with the ferric form of heme a 3, whereas carbon monoxide inhibits the ferrous form. Inhibition of the electron-transport chain also inhibits ATP synthesis because the proton-motive force can no longer be generated.

The options given above represent the complexes of electron transport chain. There are site specific inhibitors for each of the complexes of electron transport chain. It is only cytochrome oxidase that is inhibited by Cyanide.

For further details- follow the link given below

http://www.namrata.co/inhibition-of-oxidative-phosphorylation/

 

 

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1. Which of the following enzymes is not present in adipose tissue?

a) Hexokinase

b) Glycerol kinase

c) Phosphofructokinase

d) Hormone sensitive lipase

e) Acetyl co A carboxylase

Answer- b) The right answer is Glycerol kinase. It is absent in adipose tissue, that is the reason glycerol released by hydrolysis of triglycerides cannot be reutilized there . It is a waste product. It is transported through blood to liver where it is first phosphorylated to form Glycerol-3-P, by glycerol kinase and then converted to Dihydroxy acetone phosphate by the action of glycerol-3-P dehydrogenase. DHAP can be either used for glucose production or oxidized through glycolysis as per the need. In adipose tissue glycerol-3-p is obtained through glycolysis from dihydroxy acetone phosphate for esterification to form triglyceride.

Hexokinase and Phosphofructokinase are enzymes of glycolytic pathway, they are present in muscle. Hormone sensitive lipase is the enzyme for breakdown of triglycerides; it is present in adipose tissue. Acetyl co A carboxylase is the rate limiting enzyme of fatty acid synthesis, it catalyzes the first step of conversion of acetyl co A to malonyl co A, and it is present in adipose tissue.

2. A postpartum woman from a rural community recently gave birth to a baby boy with the aid of a midwife at home. She now brings the baby to the hospital because of continued bleeding and oozing from the umbilical stump. It is likely that this bleeding diathesis is secondary to a deficiency of which vitamin?

a) Vitamin A

b) Vitamin K

c) Vitamin E

d) Vitamin D

c) Folic acid

The right answer is-b) Vitamin K. Newborn infants are at risk of developing vitamin K deficiency, and this coagulation abnormality leads to serious bleeding. Transplacental transfer of vitamin K is very limited during pregnancy, and the storage of vitamin K in neonatal liver is also limited. This makes the newborn infant uniquely vulnerable to hemorrhagic disorders unless exogenous vitamin K is given for prevention of bleeding immediately after birth.

Vitamin A has a role in vision, repair, reproduction and maintenance of epithelial structures. Deficiency is known to cause ophthalmological defects leading eventually to blindness.

 Vitamin E is primarily an antioxidant and has also a role in reproduction.

Vitamin D – Its main function is in the regulation of calcium absorption and homeostasis. It has no role in coagulation of blood. Deficiency causes rickets in children and osteomalacia in adults.

Folic acid has a role in nucleotide synthesis and acts as a carrier of one carbon fragments. Deficiency causes megaloblastic anemia.

3. A 40- year-old male presents with excruciating pain in his left flank. He is diagnosed to have a kidney stone and is prescribed citrate to help prevent future stone formation. In the TCA cycle, Citrate is isomerized to Isocitrate and that is subsequently oxidized to α- Keto glutarate by Isocitrate dehydrogenase, a regulatory enzyme of TCA cycle. Which of the following would be most likely to inhibit Isocitrate dehydrogenase?

a) ADP

b) Acetyl co A

c) NADH

d) FADH2

e) Co ASH

Answer- The right answer is- c)

Isocitrate dehydrogenase is inhibited by excessive concentration of NADH. The three NAD+ dependent enzymes of TCA cycle; Isocitrate dehydrogenase, α-keto glutarate dehydrogenase and Malate dehydrogenase are inhibited by accumulation of NADH. Since three reactions of the TCA cycle as well as PDH utilize NAD+ as co-factor it is not difficult to understand why the cellular ratio of NAD+/NADH has a major impact on the flux of carbon through the TCA cycle. Thus, activity of TCA cycle is immediately dependent on the supply of NAD+, which in turn, is dependent upon the functioning of electron transport chain and oxidative phosphorylation.

It cannot be ADP, because ADP excess is a sign of low energy state of cell that in itself is a stimulus for the TCA activity to restore the energy balance. On the contrary excess ATP concentration  inhibits the TCA cycle (respiratory control of TCA cycle). Acetyl co A, in excess inhibits PDH complex, but it has no effect on activity of Isocitrate dehydrogenase. Since isocitrate dehydrogenase is NAD+ dependent enzyme, excess FADH2 will not affect the rate of action of enzyme. Similarly, Co ASH concentration can affect PDH complex, but it has no effect on isocitrate dehydrogenase activity.

4 . A 50-year-old female presents with severe abdominal pain. Her serum amylase and lipase levels are abnormally elevated and she is diagnosed with pancreatitis. Which linkage between glucose residues is cleaved by amylase ?

a) α- 1,4

b) α- 1,6

c) β-1,4

d) α 1,2

e) β-1,6

Answer- a) alpha – 1, 4 is the right answer.  Amylase acts on starch and glycogen to cleave α- 1, 4 glycosidic linkages. Both starch and glycogen are polymers of glucose. The two main constituents of starch  are amylose (13–20%), which has a nonbranching helical structure, and amylopectin (80–85%), which consists of branched chains composed of 24–30 glucose residues united by α-1,4 linkages in the chains and by α-1 .6 linkages at the branch points. Glycogen, a more highly branched structure than amylopectin contains chains of 12–14 α-D-glucopyranose residues (in α-1 ,4 glucosidic linkage) with branching by means of α-1 ,6 glucosidic bonds. Thus the branch point contains α- 1, 6 linkage that cannot be cleaved by amylase. Mammals lack any enzyme that hydrolyzes the β-1 ,4 bonds, and so cannot digest cellulose that consists of β-D-glucopyranose units linked by β-1 ,4 bonds to form long, straight chains strengthened by cross-linking hydrogen bonds. α 1,2 linkage, more precisely- O-α-D-glucopyranosyl-(1,2)-β -D-fructofuranoside linkage is found in sucrose that is hydrolyzed by sucraseβ-1,6 linkages are not common in nutrients.

5 . A 12-year-old -girl presents with polyuria, polydipsia and polyphagia. Blood Biochemistry reveals a glucose level of 320 mg/dl . She is diagnosed with Type 1 Diabetes mellitus, a disease characterized by a deficiency of Insulin. Which of the following would occur in this patient ?

a) Increased stores of triacylglycerol in adipose tissue

b) Deceased conversion of fatty acids to ketone bodies

c) Increased fatty acids synthesis from glucose in liver

d) Decreased synthesis of cholesterol in liver

e) Increased conversion of fatty acids to acetyl co A

Answer- The right answer is -e) Increased conversion of fatty acids to acetyl co A.  In diabetes mellitus, Insulin to glucagon ratio is reversed as a result there is a state of catabolism. Triglycerides stores in adipose tissue are decreased due to adipolysis under the influence of glucagon. In diabetes mellitus, de novo fatty acid synthesis in liver is deceased because in insulin deficiency the catalytic activity of Acetyl co A carboxylase (rate limiting – insulin dependent enzyme) is decreased, hence the overall pathway is inhibited. Cholesterol synthesis in diabetes mellitus is increased. It is expected that cholesterol synthesis would decrease in insulin deficiency since insulin stimulates the activity of HMG Co A reductase (rate limiting enzyme of cholesterol pathway), but on the contrary de novo cholesterol synthesis is increased.

In diabetes mellitus, due to non utilization of glucose, fatty acid oxidation takes place excessively to compensate for energy, as a result there is accumulation of acetyl co A (product of fatty acid oxidation). Excess acetyl co A (since TCA cycle is in a state of suppression) is channeled either towards ketogenic pathway or it is utilized for cholesterol synthesis. Uncontrolled diabetes mellitus is a commonest cause of hypercholesterolemia.

6. Which of the following is a compound formed from both a hydroxylation with an enzyme requiring vitamin C and subsequent methylation?

a) Histamine

b) GABA

c) Creatinine

d) Epinephrine

e) Serotonin

The right answer is-d) Epinephrine.

Neural cells convert tyrosine to epinephrine and norepinephrine. Tyrosine is first converted to DOPA by tyrosine hydroxylase enzyme. Dopa decarboxylase, a pyridoxal phosphate-dependent enzyme, forms dopamine. Subsequent hydroxylation by dopamine β-oxidase then forms norepinephrine. In the adrenal medulla, phenyl ethanolamine-N-methyltransferase utilizes S-adenosylmethionine to methylate the primary amine of norepinephrine, forming epinephrine.

Gamma Amino butyrate (GABA) functions in brain tissue as an inhibitory neurotransmitter by altering transmembrane potential differences. It is formed by decarboxylation of glutamate, a reaction catalyzed by L-glutamate decarboxylase

Glycine, arginine, and methionine all participate in creatine biosynthesis. Synthesis of creatine is completed by methylation of guanidoacetate by S-adenosylmethionine. Creatinine is an anhydrous product of creatine.

Serotonin (5-hydroxytryptamine), a potent vasoconstrictor and stimulator of smooth muscle contraction, is formed by hydroxylation of tryptophan to 5-hydroxytryptophan followed by decarboxylation.

7. A deficiency of biotin in higher animal is likely to be accompanied by which one of the following:

a) Defective oxidation of fatty acids to Acetyl co A

b) Decreased conversion of pyruvate to Acetyl co A

c) Defective synthesis of fatty acids

d) Decreased utilization of Acetyl co A in TCA cycle

e) Decreased formation of lactic acid in muscles

Answer- The right answer is c) – Defective synthesis of fatty acids.

Biotin is mainly required as a coenzyme for carboxylation reactions and the main examples are carboxylation of-i) pyruvate to oxaloacetate (first step of gluconeogenesis); ii) Acetyl co A to Malonyl co A (first step of fatty acid synthesis) and iii) Propionyl co A to D-Methyl malonyl co A (in the conversion of propionyl co A to Succinyl co A to gain entry to TCA cycle). In biotin deficiency, out of the given options, defective fatty acid synthesis is the most suited option because of the impaired conversion of acetyl co A to malonyl co A.

Fatty acid oxidation does not require biotin; FAD and NAD+ are the required coenzymes in beta oxidation of fatty acids.

Biotin is also not needed as a coenzyme during the conversion of pyruvate to Acetyl co A. The enzyme complex, PDH complex catalyzing this reaction requires TPP, CoASH, Lipoic acid, FAD and NAD+ as coenzymes.

In the utilization of Acetyl co A in TCA cycle. biotin is not required as a coenzyme; FAD and NAD+ are required as coenzymes.

Formation of lactic acid in muscle takes place from pyruvate in a reaction catalyzed by lactate dehydrogenase which requires NADH as a coenzyme.

8 . A 54 -year-old Native- American living on an Indian reservation in southwest Arizona presents to the clinic with impaired memory, diarrhea and a rash on the face, neck, and dorsum of hands. It is likely that the patient has a deficiency of which of the following vitamins?
a) Niacin

b) Folic acid

c) Vitamin C

d) Vitamin E

e) Vitamin B6

Answer- The right answer is a)- Niacin.

The clinical manifestations in the present case are of ‘Pellagra’, that occurs due to niacin deficiency.

Pellagra is manifested by Dementia, diarrhea, dermatitis and ‘death’ in untreated cases (4Ds). Pellagra is a common finding in Maize eaters. Maize lacks tryptophan which is an endogenous source of niacin, besides that niacin is also present in the bound form in maize that is biologically unavailable. Hence maize eaters always carry a predisposition to niacin deficiency.

Folic acid deficiency causes megaloblastic anemia.

Vitamin C deficiency causes Scurvy,

 There is no specific disorder associated with Vitamin E deficiency, but generalized neurological symptoms and infertility have been found to be associated with vitamin E deficiency.

Deficiency of vitamin B6 is manifested by skin changes (pellagra), neurological changes and Sideroblastic anemia. Vitamin B6 is required as a coenzyme in the pathway of niacin synthesis from tryptophan. Hence B6 deficiency also leads to niacin deficiency.

9 . A 40-year-old man presents with severe pain in his legs upon walking. He is diagnosed with atherosclerotic plaques in the arteries of his legs. High level of cholesterol and LDL contribute to the formation of atherosclerotic plaques. Which of the following is metabolized to form LDL?

a) IDL

b) Cholesterol

c) Cholesteryl esters

d) HDL

e) Chylomicrons

The right answer is- a) IDL.

IDL is produced from the metabolism of VLDL and IDL is further processed to form LDL.

VLDL s are produced in the liver and are secreted directly in to the blood as nascent VLDLs containing apoprotein B-100. They obtain apo CII and apo E from HDL. Apo CII is required for the activation of lipoprotein lipase whereas apo E acts as a ligand for internalization through apo B100/apo E receptors.

As VLDLs pass through the circulation triacylglycerols are degraded by lipoprotein lipase, causing VLDLs to shrink in size and become denser. Initially apo CII is returned to HDL and VLDL is converted to IDL (intermediate density lipoprotein) or VLDL remnant. IDL can be either taken up by cells through receptor mediated endocytosis that uses apo E as a ligand or apo E is returned to HDL and IDL is converted to LDL (low density lipoprotein). The primary function of LDL is to provide cholesterol to the peripheral tissues.

Cholesterol cannot be the answer, since it is through lipoproteins only that cholesterol is transported to the peripheral tissues.

Cholesteryl esters are esterified forms of cholesterol. A fatty acid is esterified at 3-OH group of cholesterol. Plasma contains both free and esterified cholesterol.

HDL transports cholesterol from peripheral tissues back to liver for degradation, it is antiatherogenic; hence it is cardio protective also called “Good cholesterol”.

Chylomicrons are transporters of dietary lipids. Upon metabolism in the similar way as VLDL, they are converted to chylomicron remnants that are removed from the circulation by liver.

10 . A 5-year-old boy presents with altered mental status, heart failure and muscle weakness. His serum level of glucose and ketone are abnormally low. He is diagnosed with primary carnitine deficiency. Had there been no carnitine deficiency, how many ATP molecules would have been produced form the complete oxidation of a fatty acid with 14 carbon atoms ?

a) 38

b) 129

c) 92

d) 36

e) 131

 The right answer is- c)- 92 ATPs.

 Fatty acid with 14 carbon atoms will undergo 6 cycles of beta oxidation and yield 7 Acetyl co A.

Number of ATPs per cycle of beta oxidation

1FADH2 = 1.5 ATPs (At the level of Acyl co A dehydrogenase)

1NADH +H+ = 2.5 ATPs (At the level of Beta hydroxy acyl co A dehydrogenase)

Total ATP yield = 4/cycle

In 6 cycles =  6×4 = 24 ATPs

Energy yield per Acetyl co A = 3X2.5 +1.5 = 9 +1(substrate level phosphorylation= 10

Total energy yield through complete oxidation of Acetyl co As=10×7 = 70

Total energy yield = 70 +24 = 94

Net energy yield = 94-2  = 92

(2 ATP used for activation of fatty acids)

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1. A 24-year-old female presents with complaints of intestinal bloating, gas, cramps, and diarrhea following a meal including dairy products. A lactose-tolerance test confirms that she has a deficiency of lactase. Which of the following dairy products could you recommend that would be least likely to cause her difficulties in the future?

a) Condensed milk

b) Cottage cheese

c) Ice cream

d) Skim milk

e) Yogurt

2. A 25 year-old female meets with her family physician. She is interested in starting a family soon and is looking for advice on what nutritional supplements would be beneficial during pregnancy. Which of the two supplements should be considered as the most important?

a) Vitamin K and copper

b) Selenium and thiamine

c) Iron and folate

d) Vitamin C and D

e) Vitamin A and E

3. A 16 -year-old girl presents with severe menstrual camping, caused by increased prostaglandin production. Prostaglandins are synthesized from which of the following?

a) Arachidonic acid

b) Glucose

c) Acetyl co A

d) Palmitic acid

e) Propionyl co A

4. A 45 -year-old man presents with multiple gunshot wounds to the abdomen. He undergoes emergent surgery during which a part of his intestine is resected. After surgery he is placed on total parenteral nutrition (TPN), an intravenous form of nutrition.TPN supplies essential fatty acids also in the diet. Which of the following is an essential fatty acid?

a) Palmitic acid

b) Linoleic acid

c) Elaidic acid

d) Oleic acid

e) Erucic acid

5. A 35 year-old woman presents with severe upper abdominal pain, nausea and vomiting. She is diagnosed with pancreatitis (an inflammation of pancreas). Her serum triglyceride level is 1500 mg/dl (normal 150-199 mg/dl). Triglycerides are primarily synthesized in which of the following tissues?

a) Skeletal muscle

b) Heart muscle

c) Liver

d) Spleen

e) Red blood cells

6. An 8 -year-old boy has been brought to emergency room with generalized tonic/clonic seizure. The child has a history of epilepsy and ataxia. Blood biochemistry reveals lactic acidosis. Upon questioning the parents state that their child was born with the disease, “Pyruvate carboxylase deficiency”. Which of the following products is the fate of pyruvate when the reaction is catalyzed by pyruvate carboxylase?

a) Lactate

b) Alanine

c) Acetyl co A

d) Oxaloacetate

e) Acetaldehyde

7. The catabolism of   1 mol of glucose to lactate in the glycolytic pathway is accompanied by the reduction of how many moles of O2?

a) 0

b) 2

c) 4

d) 8

e) 10

8. After digestion of a piece of cake that contains flour, milk and sucrose as its primary ingredients, the major carbohydrate products entering the blood are-

a) Glucose

b) Galactose and fructose

c) Glucose and galactose

d) Glucose and fructose

e) Fructose, glucose and galactose

9. Which of the following enzymes is not present in muscle?

a) Glycogen synthase

b) Lactate dehydrogenase

c) Glucose-6-Phosphatase

d) Hexokinase        

e) Phosphorylase

10. A 43-year-old man with a long history of poorly controlled hypertension presents to the emergency with a severe headache. His blood pressure is found to be dramatically elevated at 220/150 mm Hg. Which of the following products derived from amino acids, might bring down his highly elevated blood pressure?

a) Melanin

b) Nitric oxide

c) GABA

d) Dopamine

e) Serotonin

 

Answers

 1 – e) – Lactose intolerance is the inability or insufficient ability to digest lactose, a sugar found in milk and milk products. Lactase breaks down lactose into two simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream. Lactose intolerance is caused by a deficiency of the enzyme lactase, which is produced by the cells lining the small intestine. Enzyme levels are highest shortly after birth and decline with aging, despite a continued intake of lactose.

Although the body’s ability to produce lactase cannot be changed, the symptoms of lactose intolerance can be managed with dietary changes. Most people with lactose intolerance can tolerate some amount of lactose in their diet. Gradually introducing small amounts of milk or milk products may help some people adapt to them with fewer symptoms. Lactose-free, lactose-reduced milk, Soy milk and other products may be recommended.

The microorganisms that convert milk to yogurt (Streptococcus salivarius thermophilus and Lactobacillus delbrueckii  bulgaricus) metabolize most of the lactose in the milk. Yogurt is also a good source of dietary calcium. Thus yogurt would cause least difficulties and can be safely recommended to the patient.

2- c)- Pregnancy is a time of increased metabolic demand, and two of the most important supplements are Iron and folic acid ;Iron to prevent anemia and folic acid to prevent neural tube defects in the developing fetus. Copper and selenium are the trace elements that are rarely deficient. Thiamine is present in grain products. Vitamin C and D are sufficiently obtained from the diet. Vitamin A derivative are teratogenic and therefore should be avoided during pregnancy. Vitamin K deficiency is common in newborns and often the supplementation is required after birth.

3- a)- Prostaglandins are synthesized from Arachidonic acid; they cannot be synthesized from glucose, acetyl co A, Palmitic acid or propionyl co A.

Arachidonate, which may be obtained from the diet, but is usually derived from the 2nd position of phospholipids in the plasma membrane by the action of phospholipase A2, is the substrate for the synthesis of the prostanoids – prostaglandins (PG2) and thromboxane (TX2) series by the cyclooxygenase pathway, or the leukotrienes- LT4 and Lipoxins -LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate.

4- b)- Linoleic acid is the right answer.  It has 18 carbon atoms and two double bonds (ω6), octadecadienoic acid. Linoleic (ω6), α-Linolenic (ω3) and Arachidonic acid (ω6) are the essential fatty acids. Arachidonic acid is relatively non-essential since it can be synthesized from Linoleic acid in the body.

Palmitic acid is a saturated fatty acid with 18 carbon atoms. Elaidic acid, Oleic acid and Erucic acid are monounsaturated fatty acids (ω9). Elaidic and oleic are Trans and cis isomers respectively with 18 carbon atoms. Elaidic acid is the major Trans fat found in hydrogenated vegetable oils. Erucic acid has 22 carbon atoms and one double bond.

5- c) Liver is the right answer. Triglycerides are mainly synthesized in the liver but they can also be synthesized in the adipose tissue and intestinal cells. In the liver they are packaged in VLDL and are secreted in to the blood. The triglycerides synthesized in the intestine are packaged in chylomicrons and are transported to peripheral cells for utilization. Triglycerides cannot be synthesized in skeletal, heart muscle, spleen and red blood cells. They are stored in adipose tissue and liver.

6- d) The right answer is (d) – Oxalo acetate. Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate. It is the first step of gluconeogenesis and is also considered an “anaplerotic” or “filling up” or “CO2 fixation reaction” to replenish the oxaloacetate concentration in conditions of sudden influx of Acetyl co A, for the optimum functioning of TCA cycle. Biotin is required as a cofactor in this energy requiring reaction.

Lactate is the product of lactate dehydrogenase catalyzed reaction. Alanine is produced by transamination reaction catalyzed by Alanine transferase (ALT) also called SGPT (Serum glutamate pyruvate transaminase).

Acetyl co A is the product of pyruvate dehydrogenase reaction. Acetaldehyde is the product of pyruvate decarboxylase catalyzed reaction that does not occurs in human beings. This reaction is common in micro organisms and is commercially used for fermentation of glucose for wine production.

7- a) Production of lactate through glycolysis takes place under anaerobic conditions. No oxygen is used; hence the right answer is zero (0). Glycolysis can provide energy in the absence of oxygen; it is the unique pathway that can operate both aerobically as well as anaerobically. One mol of glucose yields 2 moles of lactate, with a yield of 2ATP by substrate level phosphorylation. In aerobic respiration via Electron transport chain O2 is used as a final acceptor and is reduced to water.

8) -e) – As per the ingredients the products would be- Glucose, galactose and fructose.

Flour- Starch-Starch is a polymer of glucose. The digestion of starch would produce glucose.

Milk- Lactose (milk sugar). Lactose is a disaccharide of galactose and glucose. Thus the digestion products of milk would be galactose and glucose.Sucrose is a disaccharide, made up of glucose and fructose. Digestion by sucrase in intestine would produce glucose and fructose.At the end, the net products of digestion entering blood would be – Glucose, galactose and fructose.

9- c) – Glucose-6-phosphatase is not present in muscle and does not contribute to blood glucose. Glucose-6-p produced from gluconeogenesis or from degradation of glycogen is channeled towards glycolytic pathway in muscle. Lactate dehydrogenase is not absent in muscle. In fact excessive lactate accumulation is the reason for muscle fatigue and the lactate produced from pyruvate by the action of lactate dehydrogenase is transported through blood to liver for glucose production (cori’s cycle).Hexokinase is the first enzyme of glycolytic pathway, glycogen synthase is the rate controlling enzyme of glycogenesis synthesis and phosphorylase is the rate limiting enzyme of glycogen degradation, all these three are present in muscle.

10- b) Hypertensive emergencies require immediate lowering of blood pressure. This may be accomplished with IV nitroprusside, a short-acting vasodilator with a rapid onset of action that allows for minute-to-minute control of blood pressure. Nitroprusside acts by releasing Nitric oxide (NO). Nitric oxide was previously referred as endothelial derived relaxing factor. It is a smooth muscle relaxant and a potent vasodilator. Nitroglycerin, amyl nitrite, (isobutyl nitrite or similar) and other nitrite derivatives used in the treatment of heart disease are also  converted to nitric oxide, which in turn dilates the coronary arteries, thereby increasing  the blood supply.

Melanin is derived from Tyrosine and is the major pigment of skin and hair.

GABA (gamma amino butyric acid), a decarboxylation product of glutamic acid is an inhibitory neurotransmitter.

Dopamine is derived from decarboxylation of DOPA, which is a product of tyrosine. Dopamine is used for raising the blood pressure in patients of shock. It is a stimulatory neurotransmitter.

Serotonin is derived from tryptophan; it is also a vasoconstrictor and a stimulatory neuro transmitter. Serotonin is involved in mood elevation and depression.

 

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46) – A 30-year-old man has been fasting for religious reason for several days.  His brain has reduced its need for glucose by using which of the following substances as an alternate source of energy?

a) Fatty acids

b) Beta hydroxy butyrate

c) Glycerol

d) Beta carotene

e) Amino acids

47) – A 7-year-old girl is brought to the emergency department by her parents with complaints of severe polyuria and Polydipsia. Laboratory examination reveals ketones in her urine. Which of the followings is the most likely source of ketones?

a) Fatty acid breakdown

b) Protein break down

c) Glycogenolysis

d) Gluconeogenesis

e) Glucose oxidation

48) – A breast-fed infant began to vomit frequently and lose weight. Several days later she developed jaundice, hepatomegaly and bilateral cataract. What is the possible cause for these symptoms? 

a) Galactosemia

b) Von-Gierke’s disease

c) Juvenile diabetes Mellitus

d) Hereditary fructose intolerance

e) Liver failure

49) – The major metabolic product produced under normal circumstances by erythrocytes and by muscle cells during intense exercise is recycled through liver in the Cori cycle. The metabolite is-

a) Oxaloacetate

b) Alanine

c) Glycerol

d) Lactate

e) Acetyl co A

50) – A 3-month-old infant presents with hepatosplenomegaly and failure to thrive. A liver biopsy reveals glycogen with an abnormal, amylopectin like structure with long outer chains and missing branches.  Which of the following enzymes would most likely be deficient?

a) Alpha Amylase

b) Branching enzyme

c)  Debranching enzyme

d) Glycogen phosphorylase     

e) Glycogen synthase

51) – Prior to a race, many marathon runners will try to increase their glycogen concentrations by loading up with foods with a high starch content, such as pasta. Alpha amylase secreted by the pancreas  will digest the starch into which of the following major products?

a) Amylose, amylopectin, and maltose

b) Glucose, galactose, and fructose

c) Glucose, sucrose, and maltotriose

d) Limit dextrins, maltose, and maltotriose

e) Glucose, fructose and Maltose

52) – Which of the following substrates cannot contribute to net Gluconeogenesis in mammalian liver?

a) Alanine

b) Glutamate

c) Palmitate

d) Pyruvate

e) Propionate

53) – Which of the following complications is less likely to occur in type II diabetics, as opposed to type I diabetics?

a) Retinopathy

b) Weight gain

c) Cardiovascular disease

d) Hypoglycemic coma

e) Hyperglycemic non ketotic coma.

54) –  Familial Fructokinase deficiency causes no symptoms because

a) Hexokinase can phosphorylate fructose

b) Liver Aldolase can metabolize it

c) Excess fructose does not escape in to urine

d) Excess fructose is excreted through feces

e) Excess fructose is converted to glycogen that can be stored in liver.

55) – Which of the followings generates free glucose during the enzymatic breakdown of glycogen in skeletal muscles?

a) Phosphorylase

b) α-1-6-amyloglucosidase

c) Debranching enzyme

d) Glucose-6-phosphatase

e) Branching enzyme

56)- A 30- year- old female presents with headache and blurry vision. Her blood pressure is 200/90 mm Hg. Imaging reveals that he she has a tumor that is overproducing the hormone most responsible for regulating salt and water balance  for blood pressure control. That hormone is-

a) Growth hormone

b) Glucocorticoid

c) Aldosterone

d) Epinephrine

e) Glucagon.

57) – A 60-year-old female presents with severe back pain for the past one week. Imaging reveals a compression fracture of one of the vertebrae and diffuse osteoporosis, which is a common condition resulting from calcium depletion in bones. As a treatment she should be prescribed

a) Oxytocin

b) Parathyroid hormone

c) Estradiol

c) Calcitonin

d) Prolactin

58) – A 16-year-old female presents with a fever, productive cough and rust colored sputum. She is diagnosed with bacterial pneumonia. She is a known case of type 1 Diabetes mellitus. She injects herself subcutaneously every day with exogenous insulin. As insulin is absorbed into her blood it binds to insulin receptors that activate-

a) Tyrosine kinase

b) Adenylate cyclase

c) c AMP

d) Protein kinase C

e) Phospholipase C

59) – An intern is scrubbing into a complicated surgery that is anticipated to last for 15 hours. In preparation, the intern has not eaten from the past 15 hours. After 30 hours  of fasting which of the following is most important for maintenance of normal blood glucose ?

a) Glycogenolysis

b) Gluconeogenesis

c) Triacylglycerol synthesis

d) Increased insulin release

e) Decreased muscle protein break down.

60) – During an extended period of exercise, the enzymes involved in the glycolytic pathway in muscle tissue are actively breaking down glucose to provide the muscle energy. The liver, to maintain blood glucose levels, is synthesizing glucose via the gluconeogenic pathway. Which of the following enzymes involved in these pathways would be most likely to exhibit Michaelis–Menten kinetics, that is, have a hyperbolic curve when plotting substrate concentration versus velocity of the reaction?

a) Fructose-1,6-bisphosphatase

b) Hexokinase

c) Lactate dehydrogenase

d) Phosphofructokinase 1

e) Pyruvate kinase

61) – A 24- year-old boy presents with diarrhea, dysphagia, jaundice, and white transverse lines on the fingernails. The patient is diagnosed with arsenic poisoning, which inhibits which of the following enzymes ?

a) Citrate synthase

b)  Isocitrate dehydrogenase

c) Pyruvate dehydrogenase

d) Alpha keto glutarate dehydrogenase

e) Succinate dehydrogenase.

62) – A 3-year- old boy is brought to the emergency room with abdominal pain, mental status changes and fatigue. On taking history the physician finds the  child belongs to a very poor family and lives in an old house and has the habit of licking the paint chips that have crumbled in the window sills. The physician suspects lead poisoning. Lead typically interferes with which of the following enzymes ?

a) Cytochrome oxidase

b) Protoporphyrinogen oxidase

c) ALA synthase

d) Coproporphyrinogen oxidase

e) ALA dehydratase

Answers

46 – The answer is –b) Beta hydroxy Butyrate,  a ketone body. Ketone bodies serve as alternative fuel for brain during prolonged fasting or starvation. Fatty acids due to long hydrophobic chain cannot cross blood brain barrier. Glycerol is a substrate of gluconeogenesis. In fact during prolonged fasting this is the only substrate left to provide glucose through pathway of gluconeogenesis. It can be oxidized through glycolysis after phosphorylation. Beta carotene is a provitamin; it is not a source of energy .Amino acids cannot be directly utilized, the carbon skeleton is oxidized in TCA cycle to provide energy or is used for glucose production.

47- The answer is –a) Fatty acid break down provides Acetyl co A that serves as a precursor for ketone bodies. In Diabetes Mellitus glucose utilization is impaired due to absolute or relative insulin deficiency. Fatty acid breakdown occurs to provide energy and the resultant excessive Acetyl co A enters the pathway of ketogenesis. Protein breakdown provides amino acids, 6 amino acids are ketogenic, while 14 are glucogenic. Hence protein breakdown contributes only a little towards formation of Acetyl co A. The major contribution is through fatty acid breakdown. Glycogenolysis and Gluconeogenesis produce glucose only. Glucose oxidation produces pyruvate or lactate, but in diabetes mellitus glucose utilization is impaired.

48-   The answer is –a) Galactosemia. The clinical manifestations are typical of classical Galactosemia. Bilateral cataract rules out the possibility of Von Gierke’s disease and hereditary fructose intolerance, although other symptoms are there in both these diseases. In juvenile diabetes mellitus, jaundice and hepatomegaly are not observed.

49- The answer is-d)- Lactate, the end product of glycolysis in erythrocytes and  during intense exercise in skeletal muscles ,is mobilized through Cori cycle to  liver to provide glucose by the process of gluconeogenesis. (Erythrocytes lack mitochondria so the end product of glycolysis is always lactate.  The mode of glycolysis during intense exercise is anaerobic; hence lactate is formed as a result of glycolysis.

Alanine is transported to liver through Glucose Alanine cycle. Glycerol is also similarly transported but not from the erythrocytes or skeletal muscles, rather from the adipose tissues. Glycerol is a waste product in adipose tissues since without phosphorylation it cannot be utilized and the phosphorylating enzyme glycerol kinase is absent in adipose tissues.

Acetyl co A cannot be produced since pyruvate to acetyl co A conversion takes place in mitochondria, Whereas RBCs lack mitochondria, hence this conversion is not possible.

50- The answer is-b) Branching enzyme. During the process of glycogen synthesis, branching enzyme creates branch points and further elongation is carried out by Glycogen synthase . In its deficiency stored glycogen is abnormal in chemistry, in the form of long polysaccharide chains with few branch points, resembling the structure of Amylopectin, thus this defect is also called Amylopectinosis. Alpha Amylase is an enzyme for digestion of starch and glycogen. Debranching enzyme deficiency results in the accumulation of abnormal glycogen, There is inability to remove the branch points, the resultant structure resembles Limit dextrin , thus it is also called Limit dextrinosis. Glycogen synthase deficiency is rare but even if it is there it affects overall glycogen synthesis, since glycogen synthase is the key regulatory enzyme of pathway of glycogen synthesis.

51- The answer is-d) The hydrolysis of starch is catalyzed by salivary and pancreatic amylases, which catalyze random hydrolysis of alpha (1- 4) glycoside bonds, yielding dextrins, and further hydrolysis yields a mixture of glucose, maltose, isomaltose (from the branch points in amylopectin) and maltotriose.

52- The answer is- c) Palmitate,  a fatty acid with 16 carbon atoms, is not a substrate for gluconeogenesis. Even chain fatty acids, predominantly present in our body, yield Acetyl co A upon oxidation, which can not contribute towards gluconeogenesis.  The Pyruvate to Acetyl co A conversion is irreversible and moreover both  of the carbon atoms of Acetyl co A are lost in the TCA cycle in the form of CO2. Odd chain fatty acid do act as substrates of gluconeogenesis, since propionyl co A the product of their oxidation can enter TCA cycle through formation of Succinyl co A, hence  can contribute towards Glucose production.

53- The answer is-d) Hypoglycemic coma occurs as a result of insulin over dosage in Type 1diabetes Mellitus.  It is not observed in Type 2 diabetes. Weight gain can occur in both types, it is the result of treatment with insulin or certain hypoglycemic drugs. Hyperglycemic Nonketotic hyperosmolar coma is observed in elderly patients of type 2 diabetes mellitus.

54- The answer is- a) Hexokinase is a non specific enzyme, it can phosphorylate fructose as well as other sugars but it has high km(low affinity) for fructose.  Glucose is the true substrate for this enzyme.Fructose-6-phosphatethe end product of Hexokinase reaction can enter glycolytic pathway to be utilized further, so it does not accumulate to produce the toxic effects. Liver Aldolase (Aldolase B) cleaves Fructose-1-P only, the product of fructokinase catalyzed reaction.  Aldolase A, present in all the cells of the body cleaves Fructose 1,6 bisphosphate, the product of PFK-1 catalyzed reaction of glycolysis.  Fructose can be converted to glycogen only if it is metabolized through Fructose kinase, Aldolase and subsequent steps. Since there is block at first step, further metabolism and conversion to glycogen does not take place.

55- The answer is- b) Free glucose is released by the action of α-1-6-amyloglucosidase enzyme, a component of debranching enzyme. Debranching enzyme has two components. α-[1 4] -α-[1 4] Glucan transferase and α-1-6-amyloglucosidase.Glucan transferase shifts the trisaccharide on a branch bound by α-[1- 4]  linkage to the straight chain and joins by α-[1 4] linkage. The exposed branch point is hydrolyzed by α-1-6-amyloglucosidase enzyme. Both components are present on the same polypeptide chain. Glucose-6- phosphatase does produce free glucose but it is absent in skeletal muscles. Branching enzyme is involved in creating branch point, there is no free glucose release by this enzyme.

56-  The right answer is-c)– Aldosterone. Aldosterone increases Na+ absorption in the kidney , and water is also reabsorbed resulting in an increase in blood volume and blood pressure. Growth hormone stimulates release of insulin like growth factors  and is responsible for growth and development. Glucocorticoid are important in response to stress. Epinephrine is the “fight or flight” hormone that stimulated glycogenolysis and lipolysis. Glucagon is the hormone to increase blood glucose levels during periods of fasting and starvation.

57- The right answer is-c)- Calcitonin. Calcitonin inhibits release of calcium from bone and also decreases blood calcium levels. Calcium, vitamin D and Calcitonin may be prescribed to help treat osteoporosis. Parathyroid hormone promotes calcium and phosphate mobilization from bone, increasing calcium levels. Oxytocin, Prolactin and Estradiol are not significant for calcium level regulation

58- The right answer is -a)– Tyrosine Kinase. Insulin binds to a cell surface receptor that acts as a Tyrosine kinase. Hormones such as epinephrine and Glucagon activate Adenylate cyclase which converts ATP to cAMP. Hormones such as Thyrotropin- releasing hormone(TRH) and Oxytocin activate protein kinase C. Phospholipase C acts on Phosphatidyl Inositol (membrane Phospholipid) to cleave it to Inositol triphosphate and diacylglycerol .

59- The right answer is b)- Gluconeogenesis. Approximately 2-3 hours after a meal, the liver maintains normal blood glucose level by glycogenolysis. Within 30 hours liver glycogen stores are depleted, leaving gluconeogenesis as the primary source for maintaining blood glucose levels. ketone bodies are generated, triacylglycerols are broken down and muscle protein breakdown increases.

 In the fed state, insulin is the main hormone while in the fasting state, glucagon level increases.

60- C. The activity of regulatory enzymes such as fructose-1,6-bisphosphatase, hexokinase, phosphofructokinase 1, and pyruvate kinase are frequently controlled by binding allosteric effectors. These allosteric enzymes usually exhibit sigmoidal kinetics. Lactate dehydrogenase is not controlled by allosteric effectors and therefore would be expected to exhibit Michaelis–Menten kinetics.

61- The right answer is -D , Alpha ketoglutarate dehydrogenase complex. Arsenite (the trivalent form of Arsenic) forms a stable complex with the – thiol group of lipoic acid, making that compound unavailable to serve as a coenzyme. Arsenic poisoning is however due to inhibition of the enzymes that require lipoic acid as a coenzyme. The enzymes requiring lipoic acid  are- Pyruvate dehydrogenase complex, Alpha keto glutarate dehydrogenase complex and alpha ketoacid dehydrogenase complex. The later enzymes is involved in the metabolism of branched chain amino acids. In the presence of Arsenate, induced lipoic acid deficiency causes decreased activity of said enzymes with the resultant accumulation of pyruvate, alpha keto glutarate and alpha keto acids of branched chain amino acids. There is inhibition of TCA cycle affecting brain, causing neurological manifestations and death.

Not only lipoic acid but all enzymes containing -SH groups are affected by Arsenic poisoning. Arsenate (Pentevalent form of Arsenic)can interfere with glycolysis at the step of Glyceraldeyde-3-P dehydrogenase thereby causing decreased ATP and NADH production by glycolysis, without inhibiting the pathway itself. The poison does so by competing with inorganic phosphate as a substrate for Glyceraldehyde-3-Phosphate dehydrogenase, forming a complex that spontaneously hydrolyzes to form 3-phosphoglycerate. Thus by bypassing the synthesis and dephosphorylation of 1,3 BPG, the cell is deprived of energy usually obtained from Glycolysis.

 Arsenic  also competes with phosphates for adenosine triphosphate, forming adenosine diphosphate monoarsine, causing the loss of high-energy bonds.

In the given problem, only Alpha keto glutarate dehydrogenase complex is the enzyme requiring lipoic acid, the other enzymes like citrate synthase, Isocitrate dehydrogenase and Succinate dehydrogenase enzymes areal though  enzymes of TA cycle but are unaffected in the arsenic poisoning. Similarly Pyruvate kinase (the enzyme catalyzing the last step of glycolysis ) is also not affected.

Evidences are there that it can cause inhibition of Hexokinase as well as Succinate dehydrogenase though not widely proved.

 

 Inhibition of glycolytic enzymes by Arsenate

Figure-1- Showing the effect of Arsenate on glycolytic enzyme

62)- The right answer is – e –ALA dehydratase.

 There are 2 enzymes in the pathway of Heme biosynthesis which are inhibited by Lead and these are ALA dehydratase/ Porphobilinogen synthase  and Ferrochelatase (Figure-2). As a result of inhibition, there is impaired heme biosynthesis.

One of the first manifestations of lead toxicity is anemia. Lead-induced anemia manifests as a microcytic, hypochromic anemia.

As regards other options-

a) Cytochrome oxidase is a complex of electron transport chain.

b) Protoporphyrinogen oxidase is an enzyme for the conversion of Protoporphyrinogen IX  to Protoporphyrin IX.

c) ALA synthase is the first  enzyme of heme biosynthetic pathway, that catalyzes the condensation of Glycine and Succinyl co A.

d) Coproporphyrinogen oxidase catalyzes the oxidation of Coproporphyrinogen to Protoporphyrinogen IX

 

Lead poisoning 

Figure-2- Showing inhibition of ALA dehydratase and Ferrochelatase by lead

 

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31- A 47- year-old woman passes out at work and is brought to emergency room. Her blood sugar is 34 mg/dl (normal >60 mg/dl). She is also tested for C-peptide, which is much higher than normal. What is the possible cause for this woman’s state?

a) Anorexia

b) High protein diet

c) Exogenous administration of Insulin

d) Insulin secreting Islet cell tumor

e) High glucose diet

32-A 24 -year old bride prepares for her wedding day. After her manicure and pedicure, her hair dresser uses rollers to create a new style for her hair. To create a “permanent wave”, the stylist then applies thioglcollate to break apart the-S-S- bonds in cystine units, reducing them to -SH groups. Which level of protein structure is most greatly affected by this treatment?

a) Primary structure

b) Secondary structure

c) Tertiary structure

d) Quaternary structure

e) Super secondary structure

33- Oral contraceptives are known to lower blood levels of folate and B6. Which of the following conversion processes would be directly affected?

a) Glutamate to N-Acetyl Glutamate by NAG synthase

b) Glutamate to Glutamine by Glutamine synthase

c) Glutamine to Glutamate by Glutaminase

d) Glutamate to Alpha keto glutarate by Glutamate dehydrogenase

e) Glutamate to GABA by Glutamate decarboxylase

34-In women taking thyroid hormone replacement pills, the dosage must be adjusted if they start taking birth control pills. Which one of the following best explains this situation?

a) Thyroid hormones block the action of estrogens, so the estrogen dose must be increased.

b) Estrogens block the action of thyroid hormones, so the dose of thyroid hormone must be increased.

c) Progestins block the action of thyroid hormone, so the dose of thyroid hormone must be increased.

d) Thyroid hormones stimulate the action of estrogens, so the estrogen dose must be decreased.

e) Estrogens stimulate the action of thyroid hormone, so the dose of thyroid hormone must be decreased.

35- A 57-year-old alcoholic is transported to the emergency room after sustaining an injury in a motor vehicle accident. A comprehensive metabolic panel and a serum γ- glutamyl transferase (GGT) level are ordered. The GGT is shown to be dramatically elevated. Apart from its role as a marker of alcoholism, this enzyme is also important for which of the following digestive processes?

a) Recycling of bile salts

b) Absorption of carbohydrates

c) Digestion of triglycerides

d) Absorption of amino acids

e) Digestion of carbohydrates

36-A 64-year -old man complains of acute onset of unilateral eye pain and reduction in visual acuity. On physical examination, a conjunctival injection (redness of eye),a mild-dilated and non reactive pupil is observed. Fundoscopic examination reveals cupping of the optic disc. Recognizing the signs and symptoms of glaucoma, Acetazolamide medication is prescribed to reduce the production of aqueous fluid and lower the intraocular pressure. Acetazolamide is a non competitive inhibitor of carbonic anhydrase, and therefore will cause ;

a) An increase in Km

b) A decrease in Km

c) An increase in Vmax

d) A decrease in Vmax

e) A decrease in both Km and Vmax

37-A 12- year-old Asian girl presents with nausea, vomiting and non localizing neurological signs. She has been using brightly colored facial cosmetics obtained from Abroad.

Which biochemical investigation should be appropriate?

a) Liver function tests

b) Brain scan

c) Blood protoporphyrin level

d) Estimation of zinc levels

e) Estimation of arsenate levels

38-A 43-year-old alcoholic male has been taking the drug Cimetidine for gastric reflux. His primary care physician warns that this is not a good idea given his poor liver functions, and therefore , his decreased ability to metabolize the drug by Glucuronidation. Glucuronidation involves the addition of a glucose molecule that has been changed by which of the following processes to form glucuronic acid ?

a) Oxidation

b) Reduction

c) Hydrolysis

d) Sulfation

e) Methylation

39-A 5 -year-old child presents with Hurler syndrome, which is characterized by dwarfism, hunchback, coarse facies, mental retardation, clouding of the cornea, and sensorineural deafness. The patient also has organomegaly due to accumulation of which of the followings? 

a) Glucocerebrosides

b) Sphingolipids

c) Heparan sulfate and dermatan sulfate

d) Glycogen

e) Galactose-I- Phosphate

40- As electrons are received and passed down the transport chain , the electron carriers are first reduced with the acceptance of the electron and then oxidized with loss of the electron. A patient poisoned by which of the following compounds has the most highly reduced state of most of the respiratory chain carriers?

a) Antimycin A

b) Rotenone

c) Carbon monoxide

d) Puromycin

e) Chloramphenicol

41- A 70 year-old female with Alzheimer dementia wanders away from her home. She gets lost and stays without water and food for 5 days. After 5 days of starvation, which of the following processes would provide the primary source of energy for the brain? 

a) Glycogenolysis

b) Lipolysis

c) Gluconeogenesis

d) Glycolysis

e) Ketosis

42-A 6 -month-old infant presents with stools that are pale colored, bulky, and foul smelling. Deep tendon reflexes are absent, his vision is poor, and he has difficulty in walking. He is diagnosed with Abetalipoproteinemia, caused due to an inability to synthesize lipoproteins containing apo B protein. Which of the following lipoprotein would be in normal concentration in this disorder ?

a) HDL

b) VLDL

c) LDL

d) IDL

e) Lp (a)

43-A 40-year- old male is brought to the intensive care unit after being hit by a car. He has severe internal bleeding and is transfused with multiple units of red blood cells to replace his lost blood. In order for hemoglobin to release oxygen to his tissues 2,3 bisphosphoglycerate is needed , that is synthesized in the glycolytic pathway, by RL shunt, a divergence of glycolytic pathway, unique to red blood cells. How many ATP molecules are expected to be produced per molecule of glucose when RL shunt is on in the red blood cells?

a) 2 

b) 4

c) 38

d) 36

e) ZERO

44- A 27 –year-old female with epilepsy has been taking Phenytoin to control her seizures. She is pregnant and considering the risk of potential bleeding episodes in the infant, her physician is considering to change her medicine. What biochemical activity might be deficient in the baby if her medication is continued as such?

a) Hydroxylation of proline

b) Gamma carboxylation of glutamic acid residues

c) Glucuronidation of bilirubin

d) Oxidation of lysine

e) Oxidation of glutathione.

45-A 6-month-old infant is seen in the emergency room with a fractured rib and subdural hematoma.  His serum copper level is 4.5 nM/L (Normal range is 5-11 nM/L). Developmental delay is apparent. Which of the following enzyme activity is most affected corresponding to the symptoms ?

a) Lysyl oxidase

b) Carboxy peptidase

c) Tyrosinase

d) Super oxide dismutase

e) Xanthine oxidase

Answers-

31-  d)-Insulin is synthesized in the Pre pro insulin form (Immature form of insulin)  that is cleaved to Pro insulin . Pro insulin is converted to mature functional form of insulin by removal of C-peptide . Insulin and C-peptide are synthesized  in the equimolar concentrations. In conditions of dietary deficiency of carbohydrates or in anorexia (as mentioned in the study) the stimulus for high insulin release  is not there hence the high C-peptide levels are not expected . If she had been self-administering pharmacological insulin, it would not have raised C-peptide levels. Under such condition the most likely answer is Insulin secreting Islet cell tumor.In this condition there is large excessive release of insulin to cause similar elevation in C- peptide levels.

 32- c)-  Tertiary structure is the right answer. Tertiary structure is stabilized by covalent disulfide bonds as well as by hydrophobic interactions, electrostatic interactions and hydrogen bonds. The primary structure is composed of covalent amide bonds. The secondary, super secondary and the quaternary structure are stabilized by non covalent interactions.

 33- The right answer is e). Out of all the mentioned enzymes , Glutamate decarboxylase is the only enzyme which is B6 dependent, hence GABA formation would be the only process affected by B6 deficiency.

N-Acetyl Glutamate by NAG synthase is required as a positive allosteric modifier by Carbamoyl phosphate synthetase-1 enzyme, the first enzyme of urea cycle. Glutamine formation and hydrolysis are active processes taking place in kidney, liver and brain for detoxification of ammonia and for maintenance of acid base balance especially in kidney. Glutamate dehydrogenase is exclusively present in liver and can utilize either of NAD+ or NADP+.

34-b)Estrogens partially block the action of thyroid hormones, making them less effective

35- The right answer is d). Glutathione has an important role in the absorption of amino acids. This is through Gamma glutamyl cycle or Meister cycle.

36- The right answer is d) A decrease in Vmax. Acetazolamide is a non competitive inhibitor, hence the Km value will remain the same. Had it been a competitive inhibitor, km  value would have increased, Vmax would have remained the same. Vmax does not increase in any type of inhibition. A decrease in both Km and Vmax is observed in uncompetitive inhibition.

37-c)  Many imported cosmetics contain lead. Very frequently children ingest these agents and develop lead poisoning. It is thus appropriate to measure the whole blood lead and erythrocyte protoporphyrin level since Lead inhibits the pathway of haem biosynthesis at the level of ALA dehydratase and Ferrochelatase.

38- The right answer is (a) Glucose is oxidized to  Glucuronic acid through uronic acid pathway of glucose metabolism. Gluconic acid is formed by oxidation of aldehyde group of glucose, while Glucuronic acid is formed by the oxidation of primary alcoholic group, when the aldehyde group is shielded by UDP. When both aldehyde and alcoholic groups are oxidized it is Glucosaccharic acid.

In the process of conjugation, UDP Glucuronic acid acts as s donor of glucuronic acid for conjugation of xenobiotics as well as for the endogenous harmful compounds. Addition of glucuronic acid imparts polarity to the foreign substance to make it water soluble and easily excretable.

39- The right answer is (c) In Hurler syndrome (Mucopolysaccharidosis ), there is deficiency of α-L-Iduronidase enzyme. This enzyme removes Iduronic acid from the chain and then subsequently, the other residues are removed by the specific enzymes. In its deficiency degradation of dermatan sulfate and heparan sulfate are affected. These GAGs (Gylcosaminoglycans) get accumulated in the tissues producing a variety of symptoms characteristic of this disease. These GAGs are also excreted excessively in urine.

40- The right answer is (c)- Carbon monoxide. The electron transport chain contains three proton pumps linked by two mobile electron carriers. At each of these three sites (NADH-Q reductase, cytochrome c reductase and cytochrome oxidase), the transfer of electrons down the chain powers the pumping of the protons across the inner mitochondrial membrane. The blockage of electron transfers by specific point inhibitors leads to a buildup of highly reduced carriers behind the block because of the inability to transfer electrons across the block. Antimycin A blocks the complex III, Rotenone blocks complex I and Carbon monoxide (As well as cyanide, azide, hydrogen sulfide) block complex IV. Therefore a carbon monoxide inhibition leads to a highly reduced state of all the carriers of the chain. Puromycin and Chloramphenicol are inhibitors of protein synthesis and have no direct effect upon the electron transport chain.

41- The right answer is (e). Glycogen stores are sufficient only for 24-48 hours, gluconeogenesis starts thereafter to provide glucose to brain cells. Fatty acids cannot cross the blood brain barrier due to the presence of a long hydrophobic chain thus brain cells cannot use fatty acids as a source of energy. In the starvation state (3-5 days of fasting), gluconeogenesis deceases due to reduced availability of the precursors, ketone bodies are synthesized by the liver and are used by the peripheral cells and brain as an alternative source of energy.

42- The right answer is HDL, this is the only lipoprotein that does not contain Apo B protein, rest all of them have apo B protein, HDL has all the apo proteins (A, C, D and E) and is a transporter of Cholesterol from peripheral tissues back to liver for degradation. It is antiatherogenic, that is why called,” Good cholesterol.” VLDL contains apo B100, and is a transporter of endogenous triglycerides from liver to peripheral tissues. LDL and IDL are formed from VLDL, thus they essentially contain apo B, protein. LDL is a transporter of cholesterol from liver to peripheral tissues, Excess of cholesterol is atherogenic, That is why LDL is called ” Bad cholesterol”. Lp (a) is attached with apo B-100 by disulphide linkage, it is atherogenic and its high concentration is associated with increased risk for myocardial infarction.

43- Answer- The right answer is (e) Zero ATPs. There are no mitochondria in red blood cells. The net energy yield per glucose molecule is 2 ATP. In total 4 ATP molecules are produced ( 2 ATP at the level of conversion of 1,3 bisphosphoglycerate to 3 Phosphoglycerate and the other 2 ATP at the level of conversion of Phosphoenol pyruvate to Pyruvate), these are produced by substrate level phosphorylation reactions without involving the electron transport chain (since there are no mitochondria ). 2 ATP are spent initially during priming reactions, first at the level of phosphorylation of Glucose (first reaction of glycolysis catalyzed by hexokinase/ glucokinase) and the second at the level of phosphorylation of fructose-6-P to form Fr 1,6 Bisphosphate (catalyzed by PFK-1, rate limiting enzyme of glycolysis).Thus the net energy output per glucose molecule is 4-2= 2 ATP. When RL shunt operates in RBCs the first substrate level phosphorylation (Conversion of 1,3 BPG to 3 PG) is bypassed, no ATP at this step. Thus the total energy output is 2 ATP and the net energy output considering the initial energy consumed in the priming reactions becomes 2-2= 0 ATP. 
This shunt has importance due to 2,3 bisphosphoglycerate that lowers the affinity of Hb for O2 (by maintaining it in the deoxy state) which is needed for unloading of O2 to peripheral tissues.

 RL Shunt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure- Showing RL shunt

44 – The right answer is (b) Gamma carboxylation of glutamic acid residues It is vitamin K deficiency induced by phenytoin. Hydroxylation of proline is brought about by vitamin C .Glucuronidation of bilirubin, oxidation of lysine and oxidation of glutathione are not related to phenytoin. Vitamin K is also required for bone formation. Vitamin K deficiency induced by phenytoin is also responsible for foetal malformation of bones called fetal hydantoin syndrome. The cause of haemorrhage in new born is not vitamin C deficiency but it is vitamin K deficiency, since vitamin K acts as a coenzyme for carboxylation of glutamic acid residues of factor II, VII, IX and X.

45- The right answer is -a) Lysyl oxidase. The child is suffering from Menke’s disease which is a copper deficiency disorder. Lysyl oxidase enzyme is a copper dependent enzyme, required for hydroxylation of lysine to hydroxy lysine. Vitamin C is also required for this hydroxylation reaction. This is an important step in collagen synthesis. The signs of fractured rib and subdural hematoma are due to impaired collagen formation in copper deficiency.
Carboxy peptidase is a zinc dependent enzyme required for removal of amino acid from the carboxyl terminal of a peptide during digestion.
Tyrosinase is an enzyme for melanin synthesis, that is also a copper dependent enzyme, the activity of this enzyme is also grossly affected in Menke’s disease.
Super oxide dismutase is also a copper dependent natural antioxidant enzyme.
Xanthine oxidase is a metallo enzyme, requiring molybdenum for its activity, it is required for the conversion of hypoxanthine to xanthine and then to uric acid.
Under the present circumstances of copper deprivation, the enzyme activities of all the copper dependent enzymes are affected, but in the given case, as per the signs and symptoms described the most appropriate answer is a) Lysyl oxidase.

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16-A young man with normocytic anemia, jaundice, and splenomegaly was diagnosed as having RBC pyruvate kinase deficiency after a peripheral blood smear showed spiculated cells. Since in this patient pyruvate kinase is abnormal not only is less pyruvate made but intermediates above pyruvate in the glycolytic pathway build up slowing the pathway. Which of the following products may not be made in the appropriate amounts in the RBC because of the deficiency of pyruvate?

a) Glucose

b) Oxaloacetate

c) Acetyl CoA

d) Lactate

e) Citrate

17-A morbidly obese woman decides to see her physician to begin a weight loss program. He tells her that diet and exercise play an essential role in her program. She is concerned that she does not have time to devote to exercise and wants to know if there is any pharmacological treatment for her. The physician decides to start her on Orlistat which directly inhibits absorption of fats. Which of the following steps is directly inhibited by Orlistat ?

a) Bile salt formation

b) Micelle formation

c) Pancreatic and gastric lipase

d) Absorption of Free fatty acids

e) Chylomicron formation

18- A known alcoholic was found  lying semiconscious by his landlady at the bottom of a stairwell with a broken arm,  he was  then taken to the emergency room. Initial laboratory studies showed  relatively large anion gap of 34 (normal = 9 to 15). His blood alcohol was elevated at 245 mg/dL (intoxication level = 150 to 300 mg/dL), and his blood glucose was 38 mg/dL (low normal). The patient/s large anion gap and hypoglycemia can best be explained by which of the following?

a) Decreased secretion of glucagon

b) Increased secretion of insulin

c) Increased urination resulting from the diuretic effect of alcohol

d) Inhibition of dehydrogenase enzymes by NADH

e) Inhibition of glycogenolysis by ethanol

19- Which of the following changes in hepatic metabolism best explains the increased incidence of ketoacidosis observed in type I diabetes?

a) Increased glucose uptake

b) Increased protein synthesis

c) Increased lipoprotein synthesis

d) Increased β-oxidation

e) Increased glycogen breakdown

20- A 16-month-old girl was found to have ingested approximately 30 mL of an acetonitrile-based cosmetic nail remover when she vomited 15 minutes post ingestion. The poison control center was contacted, but no treatment was recommended because it was confused with an acetone-based nail polish remover. The child was put to bed at her normal time, which was 2 hours post ingestion. Respiratory distress developed sometime after the child was put to bed, and she was found dead the next morning.
Inhibition of which of the following enzymes was the most likely cause of this child’s death?

a) Cytochrome c reductase

b) Cytochrome oxidase

c) Coenzyme Q reductase

d) NADH dehydrogenase

e) Succinate dehydrogenase

21- A 12-year-old girl is presented at the clinic with reports of frequent fainting and lethargy. The girl is 5 ft tall and weighs 80 lb. Skin fold tests show an abnormally low percentage of body fat mass. Which of the following hormones is likely to be severely diminished in the patient described above?

a) Cortisol

b) Epinephrine

c) Glucagon

d) Insulin

e) Thyroxin

22- A patient presents with a urinary tract infection and is prescribed a combination drug containing Trimethoprim and sulfamethoxazole. These drugs are effective because they do which of the following?

a) Bind to operon to prevent synthesis of bacterial mRNA

b) Block transport across bacterial cell walls

c) Inhibit bacterial synthesis of Cobalamine (B12)

d) Inhibit bacterial synthesis of THF

e) Inhibit synthesis of phospholipids in bacteria

23- A postoperative patient on intravenous fluids develops lesions in the mouth (angular stomatitis). Urinalysis indicates an excretion of 15 μg riboflavin/mg creatinine, which is abnormally low. Which of the following TCA cycle enzymes is most likely to be affected?

a) Citrate synthase

b) Isocitrate dehydrogenase

c) Fumarase

d) Malate dehydrogenase

e) Succinate dehydrogenase

24- A deficiency in thiamine (vitamin B1) would most likely lead to which of the following clinical manifestations?

a) Decrease in carboxylase enzyme activity

b) Decrease in serum lactate concentration

c) Decrease in red blood cell Transketolase activity

d) Increase in urinary methylmalonate

e) Increase in prothrombin time

25- Leukemia patients are often given the compound Leucovorin (N5-formyl THF) following treatment with the drug Methotrexate. Why is Leucovorin useful as part of this treatment protocol?

a) It facilitates the uptake of methotrexate by cells

b) It can be converted to THF by bypassing DHFR

c) It acts as an activator of Thymidylate synthase

d) It prevents the uptake of methotrexate by normal cells

e) It stimulates cells of the immune system

26-Megaloblastic anemia has two most likely causes, deficiency of folate and deficiency of cobalamin. Often treatment of patients with Cobalamine deficiency improves in terms of their hematologic features with treatment with folate but not in their neurologic symptoms. What is the most likely explanation for this explanation?

a) Cobalamine deficiencies are not serious

b) Excess folate blunts the trapping of folate as N5-methyltetrahydrofolate

c) Folate in high concentrations can serve as cofactor for the conversion of homocysteine to methionine

d) Excess folate directly inhibits the destruction of red blood cells

e) Excess folate stimulates erythropoietic tissues to synthesize cobalamin in situ

27-What would be the consequences of a deficiency of vitamin B12 on fatty acid oxidation? Which of the following  metabolic intermediates might accumulate?

a) Acetyl co A

b) Succinyl co A

c) Propionyl co A

d) Acetoacetyl co A

e) Methyl malonyl co A

28-A 30-month-old female child whose growth rate has been in the lower 10th percentile over the last year presents with chronic, nonproductive cough and diarrhea with foul-smelling stools. She is diagnosed as having cystic fibrosis. For which of the following vitamins is this child most likely to be at risk of deficiency?

a) Ascorbic acid (vitamin C)

b) Biotin

c) Folic acid

d) Retinol (vitamin A)

e) Riboflavin (vitamin B2)

29-An unskilled worker in a water garden was sent to sweep up a spill of a white powder in the storage shed. Later he was found with labored breathing and convulsions. On further examination, the white powder was identified as rotenone . Respiratory distress is induced on rotenone exposure because it inhibits the complex that catalyzes which of the following?

a) Electron transfer from NADH to coenzyme Q

b) Oxidation of coenzyme Q

c) Reduction of cytochrome c

d) Electron transfer from cytochrome c to cytochrome a1/a3

e) Electron transfer from cytochrome a1/a3 to oxygen

30- Which of the following tissues can metabolize glucose, fatty acids, and ketone bodies for ATP production?

a) Liver

b) Muscle

c) Brain

d) Red blood cells

e) White blood cells

Answers- 

16- d)- RBCs do not have  mitochondria hence glucose cannot be synthesized from pyruvate  and pyruvate can not be converted to acetyl-CoA or Oxaloacetate, because the corresponding enzymes, Pyruvate dehydrogenase complex and pyruvate carboxylase  are mitochondrial, hence these conversions are not possible.  But  RBCs do have lactate dehydrogenase enzyme and conversion to lactate is possible. The conversion depends on pyruvate levels. In the deficiency of pyruvate kinase , pyruvate concentration is low thus lactate formation is also reduced.

17- Orlistat inhibits gastric and pancreatic lipases, preventing the digestion and absorption of fats. The normal sequence of digestion is that triglycerides are emulsified by bile salts. These are then acted on by lipases. The product of digestion are absorbed and reesterified in the intestinal mucosal cells to form triglycerides which are packed in the Chylomicrons for transportation out to the peripheral cells for utilization. Under the effect of orlistat triglycerides are left undigested and unabsorbed, resulting in bulky stools. Over a period of time, orlistat therapy can induce deficiency of fat soluble vitamins.

18- d)- Alcoholics frequently do not eat while binge drinking, so it is most likely that his liver glycogen stores became depleted and he could not increase his blood glucose levels due to impaired gluconeogenesis. Key gluconeogenic dehydrogenases are inhibited by the elevated levels of NADH, including lactate dehydrogenase, glycerol 3-phosphate dehydrogenase, and malate dehydrogenase. The precursors for gluconeogenesis are not available due to shifting of equilibrium of the reactions towards formation of Lactate, glycerol-3-P and malate. Thus dietary unavailability coupled with reduced gluconeogenesis is the cause for hypoglycemia.

The large anion gap is due to lactic acidosis and keto acidosis.

Lactic acidosis is due to accumulation of lactate.The metabolic stress leads to the increase in secretion of epinephrine and other hormones that mobilize fatty acids from stored triglycerides in adipose cells. These fatty acids undergo β-oxidation in the liver and are converted to ketone bodies because of the inhibition of the TCA cycle by high levels of NADH produced by the oxidation of ethanol first to acetaldehyde and acetate. Thus excess Acetyl co A is converted to ketone bodies causing ketoacidosis.

19- d)- Decreased circulating insulin signals a need to increase hepatic glucose production. This is an energetically demanding process, driven by β-oxidation of fatty acids. However, acetyl-CoA, the major end product of β-oxidation, cannot be used for glucose production. Instead, acetyl-CoA is shunted into the pathway of ketone body synthesis (ketogenesis). In contrast, carbon from intrahepatic glycogen will contribute less to ketone body synthesis in uncontrolled type I diabetes mellitus. Net glucose uptake, protein synthesis, and lipoprotein synthesis are decreased in uncontrolled type I diabetes.

20- b. The culprit here is cyanide produced from acetonitrile. Cyanide inhibits the cytochrome oxidase of electron transport chain .

21- d. The low body weight and fat mass observed in the patient are consistent with a metabolically “fasted” state. During such a condition, circulating insulin levels will be low, whereas counter regulatory hormones (e.g., glucagon, epinephrine, and cortisol) will be elevated.

22- d) Bacteria must synthesize folate that is required for their biosynthetic processes; they do not have a transporter to bring folate into the cell. Trimethoprim inhibits prokaryotic DHFR (eukaryotic is not affected) and sulfamethoxazole is an analog of p-amino benzoic acid (PABA), a precursor to folic acid. Bacteria will use this analog instead of PABA and produce a nonfunctional folate. Both are examples of competitive inhibition.

23- e)-The patient has demonstrated a deficiency in riboflavin (urinary excretion of less than 30 μg/mg creatinine is considered clinically deficient). Riboflavin is a component of the cofactor FAD (flavin adenine dinucleotide), which is required for the conversion of succinate to fumarate by succinate dehydrogenase.

24- c) In addition to being an important cofactor for the enzymes involved in the oxidative decarboxylation of pyruvate, α-ketoglutarate, and branched-chain α-ketoacids, thiamine is also a cofactor for the enzyme Transketolase, the enzyme that transfers aglycoaldehyde group from a ketose sugar to an aldose sugar in the pentose phosphate pathway.
One of the diagnostic tools in determining a thiamine deficiency is determination of the activity of red blood cell Transketolase in the presence and absence of added thiamine. A thiamine deficiency would be expected to increase blood lactate concentrations. A deficiency of biotin would lead to decreased carboxylase activity, whereas an increased methylmalonate concentration would be
observed with a deficiency in vitamin B12. A deficiency in vitamin K would lead to an increase in prothrombin time.

25- b) Leucovorin (N5-formyl THF, folinic acid) is used as an antidote for cells that have decreased levels of folic acid. Treatment of leukemia patients with methotrexate kills the tumor cells but also other normal rapidly dividing cells. N5-formyl THF is normally administered 24 hours following treatment with methotrexate; it can be converted to THF by these normal cells by bypassing the block caused by methotrexate. Therefore, these normal cells can synthesize deoxythymidine and carry out DNA synthesis. Methotrexate inhibits dihydrofolate reductase enzyme.

26- b) Excess folate, by overwhelming the folate pool trapped as N5- methyl tetrahydrofolate, can allow for formation of N5,N10-methylene tetrahydrofolate which is required for the thymidylate synthase reaction for DNA synthesis and red blood cell formation. Folate is not recognized as a methyl donor by methionine synthase. Folate does not inhibit destruction of erythrocytes. Cobalamine is an important critical vitamin not synthesized by humans.

27 – e)-Vitamin B12 is a coenzyme prosthetic group for methylmalonyl-CoA mutase. This enzyme is active in metabolism of odd-chain fatty acids. The last round of β oxidation releases acetyl-CoA and propionyl-CoA from odd-chain fatty acids. Propionyl-CoA is further metabolized by being converted to (D)-methylmalonyl-CoA by propionyl-CoA carboxylase, a biotin-containing enzyme. (D)-Methylmalonyl-CoA racemase then converts (D)-methylmalonyl-CoA to (L)-methylmalonyl-CoA, which is metabolized to succinyl CoA by methylmalonyl-CoA mutase. This enzyme is a vitamin B12-dependent enzyme, and a deficiency in vitamin B12 will cause a build-up of (L)-methylmalonyl-CoA. 

Depending on the amount of odd chain fatty acids (and Propionic acid) in the diet, a deficiency of B12 is expected to act as a coenzyme A trap, slowly accumulating coenzyme A as methylmalonyl-CoA. The affected patients present with Methylmalonic aciduria.

28- d)  Because cystic fibrosis leads to pancreatic damage and diminution of the ability to secrete HCO3 ions and pancreatic digestive enzymes with the result that fat and protein are absorbed poorly. Retinol is a fat soluble vitamin that must be absorbed along with lipid micelles; other fat-soluble vitamins are E, D, and K. The other vitamins listed are water-soluble and their absorption is not significantly affected. Hence in cystic fibrosis fat soluble vitamin deficiency(vitamin A in the given case) is expected.

29 – The right answer is a).

Rotenone binds avidly to the flavoprotein NADH CoQ reductase, complex I (also called NADH dehydrogenase). The central portion of the rotenone structure resembles the isoalloxazine ring of the FMN molecule, and when it binds to complex I, rotenone prevents the transfer of electrons from NADH to coenzyme Q.

 30- The right answer is (b). Muscle cells are the only cells that are capable of utilizing all the energy sources available- glucose, fatty acids and during starvation ketone bodies. Mitochondria are required for the utilization of fatty acids and ketone bodies. Since red blood cells do not contain mitochondria, no utilization of these energy sources is possible. Although brain can utilized glucose and ketone bodies but the fatty acid cannot cross through blood brain barrier. Liver cells are the sites for ketone body production, but the mitochondrial enzyme necessary for utilization of ketone bodies is not present in hepatocytes.

 

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1- A 38-year- old woman sees an advertisement for a new weight loss medication. The ad claims that the drug causes your body to burn calories without having to exercise. In theory which of the following compounds could make this claim ?

a) Rotenone

b) Antimycin

c) Dinitrophenol

d) Amytal

e) Atractyloside

2-A 65 year-old man with a long history of diabetes presents to his physician after failing the driver’s license renewal eye examination. Patients with diabetes have abnormally high blood glucose levels. Glucose can enter the lens of the eye, where it can be converted to Sorbitol. Which of the followings converts glucose to Sorbitol ?

a) Hexokinase

b) Aldose reductase

c) Sorbitol dehydrogenase

d) Aldose oxidase

e) Glucokinase

3- A 40-year-old, obese woman presents with acute pain in the right upper quadrant of her abdomen as well as vomiting. She is diagnosed with gall stones and is placed on ursodeoxycholate, a bile salt used to inhibit the formation of cholesterol gall stones by facilitating dissolution of cholesterol. 
Which of the following is also a bile salt ?

a) HMG Co A

b) Mevalonate

c) Lanosterol

d) Squalene

e) Glycocholate

4-High carbohydrate ingestion leads to obesity, Which one out of the followings is the most important cause   ?

a) More formation of NADPH

b) More formation of fatty acids

c) More formation of glycerol

d) None of the above

e) All of the above.

5-An 18 month-old- child is left unattended while in the kitchen and ingests a small portion of rat poison found in the cupboard found under the sink. The ingredient fluoroacetate reacts with Oxaloacetate to form fluorocitrate. Which pathway of the body is inhibited by this poison ?

a) Glycolysis

b) TCA cycle

c) Fatty acid oxidation

d) Fatty acid synthesis

e) HMP pathway

6- An infant is born with a high forehead, abnormal eye folds, and deformed ear lobes. He shows little muscle tone and movement. After multiple tests, he is diagnosed with Zellweger syndrome, a disorder caused by malformation of peroxisomes. 
Which of the following is expected to be high in concentration in brain tissue of the affected individual ? 

a) Ketone bodies

b) Lactate

c) Cholesterol

d) Very long chain fatty acids

e) Branched chain amino acids

7-A 23-year-old, boxing contender presents with assorted metabolic disorder , most notably ketosis. During the history and physical examination, he describes his training regimen, involves consuming a dozen raw eggs a day for protein. Raw eggs contain a protein called Avidin, with an extremely high affinity for a cofactor required for the propionyl co A carboxylase and Acetyl co A carboxylase. Name the cofactor which gets deficient by consumption of raw eggs.

a) B12

b) Vitamin C

c) Vitamin E

d) Folic acid

e) Biotin

8-A 40 -year-old woman presented with chest pain. Her blood biochemistry report did not reveal significant changes and ECG was also normal. Her family history was positive for IHD. She was kept under observation and was discharged later after a few hours. She was advised to start a low dose of Aspirin. Aspirin is considered cardio protective, since it inhibits cyclo -oxygenase (COX) enzyme.
COX is required for the production of which of these ?

a) Thromboxane from arachidonic acid

b) Leukotrienes from Arachidonic acid

c) Phospholipids from Arachidonic acid

d) Arachidonic acid from Linoleic acid

e) Linolenic acid from Arachidonic acid

9-A 71-year-old man had a 3 week history of weakness, polyuria, intense thirst, difficulty in speaking and understanding commands, staggering walk, confusion and a weight loss of 10 kgs. For one month he took 200,000 units of vitamin D each day because he had severe osteoarthritis. His plasma calcium was 3.38 mmol/L(13.5 mg/dl)
What is the most probable diagnosis?

a) Diabetes Insipidus

b) Renal failure

c) Diabetes mellitus

d) Hypervitaminosis D

e) Hypothyroidism

10- A young infant, who was nourished with a synthetic formula, had a sugar in the blood and urine. This compound gave a positive reducing sugar test but was negative when measured with glucose oxidase(specific test for detection or estimation of Glucose). Treatment of blood and urine with acid (which cleaves glycosidic bonds) did not increase the amount of reducing sugar measured. Which of the following compounds is most likely to be present in this infant’s blood and urine ?

a) Glucose

b) Fructose

c) Maltose

d) Sorbitol

e) Lactose

11- A gall stone that blocked the upper part of the bile duct would cause increase in which of the followings ?

a) The excretion of fats in the feces

b) Formation of chylomicrons

c) Excretion of bile salts

d) Conjugation of bile acids

e) Recycling of bile salts

12- A 3-year-old Caucasian female presents with chronic diarrhea and a failure to thrive. Stools were oily. History reveals that she was breastfed and had no problems until she was weaned. Which of the enzymes would be expected to be deficient following stimulation with secretin?

a) Cholesteryl esterase

b) Gastric lipase

c) Hormone sensitive lipase

d) Lipoprotein lipase

e) Pancreatic lipase

13- Which of the following is least likely to contribute to the hyperglycemia associated with uncontrolled type I diabetes?

a) Decreased skeletal muscle glucose uptake

b) Decreased adipose lipogenesis

c) Increased adipose lipolysis

d) Increased hepatic gluconeogenesis

e) Increased skeletal muscle glycogenolysis

14- After excessive drinking over an extended period of time while eating poorly, a middle-aged man is admitted to the hospital with “high output” heart failure. Which of the following enzymes is most likely inhibited?

a) Aconitase

b) Citrate synthase

c) Isocitrate dehydrogenase

d) α-Ketoglutarate dehydrogenase

e) Succinate thiokinase

15-Which of the following complications is less likely to occur in type II diabetics, as opposed to type I diabetics?

a) Retinopathy

b) Weight gain

c) Cardiovascular disease

d) hypoglycemic coma

e) Neuropathy

Answers to Multiple Choice Questions

1- The right answer is-c)  Dinitrophenol. The mechanism of action of the drug is through uncoupling of oxidative phosphorylation and Dinitrophenol is the only uncoupler in the list, rest all inhibitors of ETC except, Atractyloside which is an inhibitor of ATP/ADP transporter.

2- The right answer is b) Aldolase reductase. Hexokinase and Glucokinase are enzymes for phosphorylation of glucose in the pathway of glycolysis and sorbitol dehydrogenase is an enzyme to convert sorbitol to fructose. It is absent in most of the tissues except for liver, seminal epithelium and testicular tissue. Aldose oxidase has no role to play. Had sorbitol dehydrogenase been there in all tissues, diabetes related complications would not have occurred, though this is not the only mechanism responsible for causing complications but a major contributor.

3- The right answer is-e)  Glycocholate. Bile salts and phospholipids keep cholesterol in the soluble form. Any condition that causes less bile salt or more cholesterol formation leads to precipitation of cholesterol . Initially crystals are formed which upon accumulation from stones. Synthetically prepared bile salt, ursodeoxy cholic acid is given for dissolution of cholesterol stones to those patients who do not want surgery or are not fit for surgery. Cholecystectomy is the ultimate cure for symptomatic gall stones. In majority of cases gall stones do not cause symptoms.

4- Excessive carbohydrate consumption leads to obesity The right answer is -e)
1) Excess glucose available- two main pathways of glucose utilization provide Precursors for lipogenesis
A) HMP pathway- Provides NADPH for reductive biosynthesis
 Glycolysis- Provides Acetyl co A and Glycerol-3-p
a) Excess of Pyruvate from glucose- Excess of Acetyl co A – Excessive fatty acid synthesis
b) Excess of glycerol-3-p – available from Dihydroxy acetone Phosphate
Esterification of Glycerol-3-P with fatty acids to form Triglycerides- Increased adipose mass and hence Obesity.

5 – The right answer is -b) TCA cycle

Fluoroacetate first gets converted to Fluoroacetyl coA then condenses with Oxaloacetate to get converted to Fluorocitrate to inhibit Aconitase enzyme of TCA cycle. It is an example of suicidal inhibition.

6-The right answer is d)-“Very long chain fatty acids”. Very long chain fatty acids are first trimmed in the peroxisomes till the length of C16 or C18, then they are transported to mitochondria in the conventional way though carnitine shuttle to be oxidized completely by beta oxidation. In Zellweger syndrome the peroxisomal trimming is impaired, thus VLFA accumulate in brain and blood of affected patients.

7- The right answer is e)- Biotin. Egg white contains Avidin, that binds with high affinity to Biotin. Biotin is the cofactor required for conversion of Propionyl co A to D-Methyl malonyl co A and also for the conversion of Acetyl co A to Malonyl co A. Consumption of raw eggs promotes formation of Avidin- Biotin complex causing Biotin deficiency, known as Egg white injury. The said complex is not formed if the same number of cooked eggs are ingested, since cooking causes denaturation of Avidin and that loses the ability to bind with biotin.

8- a) Aspirin irreversibly acetylates cyclo-oxygenase-1 of platelets and inhibits the enzyme so that Thromboxane (TxA2) is not formed. So there is no vasoconstriction and no platelet aggregation and hence the thrombus formation is prevented.
At the same time Aspirin also inhibits production of Prostacyclin (PGI2) by endothelial cells, which prevents platelet aggregation and produces vasodilatation. But unlike platelets, the endothelial cells regenerate cyclo-oxygenase within a few hours. Thus the overall balance shifts towards prevention of thrombus formation by promoting the Prostacyclin formation. Aspirin is clinically used for the prevention and management of Angina. Myocardial infarction, Stroke and Transient Ischaemic attacks (TIA).

9- d)- It is a case of vitamin D toxicity. Usually, vitamin D toxicity results from taking excessive amounts. Because synthesis of 1,25(OH)2D (the most active metabolite of vitamin D) is tightly regulated, vitamin D toxicity usually occurs only if excessive doses (prescription or megavitamin) are taken. Marked hypercalcemia commonly causes symptoms. Anorexia, nausea, and vomiting can develop, often followed by polyuria, polydipsia, weakness, nervousness, pruritus, and eventually renal failure. Proteinuria, urinary casts, azotemia, and metastatic calcifications (particularly in the kidneys) can develop.
Diagnosis is typically based on elevated blood levels of 25(OH)D. Treatment consists of stopping vitamin D, restricting dietary Ca, restoring intravascular volume deficits, and, if toxicity is severe, giving corticosteroids or bisphosphonates.

10 – The right answer is b)- fructose. Glucose cannot be there since specific test is negative. Sorbitol is non reactive to reduction test. Maltose and lactose would have caused increase in the amount of reducing sugar upon acid hydrolysis. Hence it is fructose which is reducing in nature nut non reactive to glucose oxidase.

11- The right answer is-a)  excretion of excess fats in the feces, In this situation, bile salts cannot enter the digestive tract. therefore recycling and excretion of bile salts, digestion of fats, and formation of chylomicrons is decreased. As a consequence fats in the feces are increased (Steatorrhea).

12- e),  Neither hormone sensitive lipase nor lipoprotein lipase is a digestive enzyme. The patient’s symptoms are consistent with an inability to absorb triglycerides, which would eliminate cholesteryl esterase from consideration. Since the patient did not have any problem while being breast-fed, then the most likely enzyme to be deficient is pancreatic lipase, since gastric lipase is most active on short chain triglycerides, such as those that are found in breast milk.

13- e)- Unlike the liver, skeletal muscle cannot export glucose into the circulation.
Once glucose enters the myocyte, it is destined for use by that cell. Thus, intramyocellular glycogen is used as a fuel source by skeletal muscle and therefore cannot contribute to the hyperglycemia observed in uncontrolled type I diabetes. In contrast decreased insulin mediated glucose utilization by skeletal muscle and adipose will contribute to hyperglycemia, as will decreased insulin-mediated suppression of hepatic glucose output. Decreased insulin-mediated suppression of lipolysis will indirectly contribute to hyperglycemia, by providing alternative, non-glucose, fuels (fatty acids and ketone bodies) or organs such as skeletal muscle and the liver.

14- d)- This patient has exhibited symptoms of beriberi heart disease, which is a result of a nutritional deficiency in vitamin B1 (thiamine). The active form of the vitamin, thiamine pyrophosphate, is a required cofactor for α-ketoglutarate dehydrogenase.

15- d)-  Hypoglycemia is a common complication associated with over supplementation of type I diabetics with insulin. This is less common in type II diabetics, because insulin therapy generally occurs only in the later stages of the pathogenesis of this disease. Retinopathy, cardiovascular disease, and neuropathy are common complications associated with both forms of diabetes mellitus. In contrast to type I diabetics, type II diabetics tend to be overweight. Whether weight gain is a cause or consequence of disease progression is under current debate.

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Q.1-The p H of the body fluids is stabilized by buffer systems. Which of the following buffers is the most effective buffer system at physiological pH?                                 

a) Bicarbonate buffer                                                 

b) Phosphate buffer

c) Protein buffer                                                         

d) Deoxy hemoglobin

Q.2-Which of the following laboratory results below indicates compensated metabolic alkalosis?                                                                                                                  

a) Low p CO2, normal bicarbonate and, high pH     

b) Low p CO2, low bicarbonate, low pH

c) High p CO2, normal bicarbonate and, low p H     

d) High pCO2, high bicarbonate, High pH.

Q.3Which of the following has the highest glycemic index?                               

a) Ice cream                                                                

b) Cucumber

c) Bread                                                                     

d) Dextrose

Q.4-In diabetes mellitus there is reduced oxidation of carbohydrates; what will the effect of insulin administration on RQ?                                                                                

a)  It will increase                                                       

b) It will decrease

c) No effect                                                                

d) Initial rise and then fall

Q.5-Which of the following nutrients is rich in short and medium chain fatty acids

a) Milk                                                                        

b) Peanut oil

c) Sunflower oil                                                         

d) Almond oil

Q.6- A woman’s risk for developing breast cancer is greatest with:                   

a) Family history of breast cancer and a history of taking hormone replacement therapy

b) Early age at menarche and late age of first parity

c) A family history of breast cancer and a history of benign breast disease

d) A BRCA1 or BRCA2 mutation.

Q.7-Reduction of the 2′-hydroxyl of purine and pyrimidine Ribonucleotides, catalyzed by-

a) Thioredoxinreductase                                           

b) Ribonucleotide reductase

c) Dihydro folate reductase                                        

d) Oxidoreductase.

Q.8-Human brain has a low level of which of the following enzymes?               

a) PRPP synthetase                                                    

b) Amidotransferase

c) HGPRT                                                                  

d) Adenosine deaminase

Q.9- The fragments of newly synthesized DNA are sealed by enzymes referred to as –

 a) Restriction endonucleases                                     

b) Topo isomerases

c) Telomerases                                                

d) DNA ligases.

Q.10- In animal cells, including human cells, the replication of the DNA genome occurs only at a specified time during the life span of the cell. This period is referred to as the

a) gap 1(G1)                                                               

b) gap 2(G2)

c) M phase                                                      

d) S phase.

Q.11- The derepression of lac operon in the presence of lactose is an example of-        

a) Positive regulation                                                 

b) Negative regulation

c) Double negative regulation                                    

d) Double positive regulation.

Q.12- The operator locus is a region of double-stranded DNA-                          

a) To bind RNA polymerase                                      

b) To bind lac repressor

c) To bind CAP-cAMP complex                               

d) To bind transcription factors

Q.13- Which of the followings is not a stop codon in prokaryotes?                     

a) UAA                                                                      

b) UAG

c) UGG                                                                      

d) UGA

Q.14- The ideal support medium for separation of nucleic acids is-                    

a) Starch gel                                                               

b) Cellulose acetate

c) Agarose gel                                                            

d) Filter paper

Q.15- The drug Aspirin is detoxified by-                                                               

a) Methylation                                                            

b) Acetylation

c) Hydrolysis                                                              

d) Glucuronidation

Q.16- Which of the following enzymes is not a tumor marker?                           

a) Alkaline phosphatase                                             

b) Acid phosphatase

c) Lactate dehydrogenase                                          

d) Acid maltase

Q.17- DNA is assembled into nucleosomes with the help of special proteins called-

a) Prolamines                                                  

b) Histones

c) Chaperones                                                            

d) Protamines

Q.18- Burkitt’s lymphoma is caused by-                                                                

a) Adeno virus                                                                       

b) Human Papilloma virus

c) Hepatitis B virus                                                    

d) Epstein – Barr virus

Q.19- Which drug out of the following is not an anticancer drug?         

a) Azaserine                                                               

b) Allopurinol

c) Cytosine arabinoside                                              

d) Mercaptopurine.

Q.20- Which out of the followings is not a true mechanism for conversion of proto oncogenes to oncogenes?                                                                                               

a) Point mutation                                                       

b) Chromosomal translocation

c) Insertional mutagenesis                                          

d) Histone acetylation

 

 

Key to answers-

1)-a,2)-d,3)-d,4)-a,5)-a,6)-d,7)-b,8)-b,9)-d,10)-d,11)-c,12)-b,13)-c,14)-c,15)-c,16)-d,17)-b,18)-d,19)-b,20)-d

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Q.1- S- Adenosyl Methionine (Active Methionine )is required for the synthesis of all of the following compounds except-

a) Thymine                                                                 

b) Nor epinephrine

c) Epinephrine                                                            

d) Melatonin            

Q.2-Which out of the following compounds is not an inhibitor of complex IV of electron transport chain?

a) CO                                                                         

b) H2S

c) BAL                                                                       

d) CN.                        

Q.3-The inner mitochondrial membrane is rich in which of the following phospholipids?

a) Cardiolipin                                                             

b) Lecithin

c) Cephalin                                                                 

d) Plasmalogen         

Q.4The conversion of Pyruvate to Acetyl co A involves the participation of all except –
a) Niacin                                                                     

b) Riboflavin

c) Biotin                                                                     

d) Pantothenic acid.   

Q.5Which out of the followings is a fatty acid with 18 carbon atoms and one double bond in the trans configuration?

a) Palmitoleic acid                                                      

b) Oleic acid

c) Erucic acid                                                             

d) Elaidic acid.            

Q.6Which out of the followings is an ω 6 fatty acid?

a) Linolenic acid                                                        

b) Linoleic acid

c) Palmitic acid                                                          

d) Arachidic acid.     

Q.7-“Phospho enol pyruvate carboxy kinase”is an enzyme of which of the following pathway?

a) Glycolysis                                                              

b) Gluconeogenesis

c) Pentose phosphate pathway                                    

d) Glycogenolysis.    

Q.8-Which out of the followings is not a hemoprotein?

a) Tryptophan pyrrolase                                             

b) Tyrosinase

c) Myoglobin                                                              

d) Cytochrome P450. 

Q.9-Which of the following monosaccharides is not a carboxylic acid?

a) Glucuronate                                                                       

b) Gluconate

c) Glucose                                                                  

d) Muramic acid.       

Q.10 Which of the following apoproteins is an activator of lipoprotein lipase?

a) Apo A                                                                    

b) Apo B

c) Apo C II                                                                

d) Apo D.              

Q.11-Which of the following vitamins is used as a hypolipidemic drug?

a) Thiamine                                                                

b) Niacin

c) Folic acid                                                              

 d) Pantothenic acid     

Q.12-Malonyl co A is a direct inhibitor of which of the following enzymes of fatty acid oxidation?

a) Carnitine Acyl Transferase –I                                

b) Carnitine Acyl Transferase –II

c) Thiokinase                                                              

d) Thiolase             

Q.13-Which of the following enzymes requires adenosine triphosphate (ATP) for its action?

a) Argino Succinate lyase                                          

b) Argino Succinate synthetase

c) Arginase                                                                 

d) Glutaminase.    

Q.14-Which out of the followings is not a fibrous protein?

a) Carbonic anhydrase                                                           

b) Collagen

c) Fibrinogen                                                              

d) Keratin.                   

Q.15-Which of the following enzymes is not present in muscle?

a) Phosphorylase b                                                     

b) Hexokinase

c) Glucose-6-phosphatase                                          

d) Glycogen synthase 

Q.16-A 78-year-old male is brought to emergency with acute myocardial infarction. Blood biochemistry reveals lactic acidosis. How much energy yield (ATP) per mol of glucose is expected in such a condition?

a) 32                                                                           

b) 2

c) 34                                                                           

d) 36                      

Q.17-Pasteur effect is due to inhibition of glycolysis by high concentration of –

a) Creatine phosphate                                                

b) ATP

c) ADP                                                                       

d) AMP               

Q.18-The citric acid cycle is inhibited by which of the followings?

a) Fluoroacetate                                                         

b) Fluoride

c) Malonyl co A                                                         

d) Fluorouracil.           

Q.19-The key regulatory enzyme of HMP pathway is-

a) Glucose-6-P dehydrogenase                                

 b) Transaldolase

c) Transketolase                                                         

d) 6-P-Gluconate dehydrogenase.     

Q.20-A mutation has changed an Isoleucine residue of a protein to Glutamic acid, which statement best describes its location in a hydrophilic exterior-

a) On the surface since it is hydrophilic in nature

b) Inside the core of the protein since it is hydrophobic in nature

c) Any where inside or outside

d) Inside the core of protein since it has a polar but uncharged side chain.

 

Key to answers- 1)-b, 2- c, 3)-a, 4)-c, 5)-d, 6)-b, 7)-b, 8)-b, 9)-c, 10)-c, 11)-b, 12)-a, 13)-b,14)-a, 15)-c,16)-b,17)-b,18)-a,19)-a,20)-a

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Q.1- A 50- year-old male is seen in the emergency with severe headache. His blood pressure is 210/130 mm Hg. An evidence of retinal hemorrhage and epistaxis is also there. He has been given an infusion of nitroprusside. Which of the following processes is directly affected by the active metabolite of this drug?

a) Phospholipase A2                                                                 

b) Phospholipase C

c) Guanylate cyclase                                                                

d) Phosphodiesterase

Q.2- Phenylketonuria is characterized by-

a) Urine turning black on standing                                           

b) Wolf like smell of urine

c) Mousy odor of urine                                                                 

d) Smell of burnt sugar of urine

Q.3- The active form of Methionine is-

a) S- Acetyl methionine                                                                

b) S- Carboxyl methionine

c) S- Adenosyl methionine                                                          

d) N-acetyl methionine

Q.4- Patients with inherited defects of mitochondria involving components of the respiratory chain and oxidative phosphorylation present with all except-

a) Myopathy                                                                                     

b) Lactic acidosis

c) Encephalopathy                                                                          

d) Mental retardation

Q.5- Which of the followings best describes the toxicity associated with Atractyloside

a) Acts as an inhibitor of ETC                                                      

b) Acts as an uncoupler

c) Acts as an inhibitor of ATP/ADP transporter                   

d) Inactivates ATP synthase complex

Q.6- A given substrate may be acted on by a number of different enzymes, each of which uses the same substrate(s) and produces the same product(s). The individual members of a set of enzymes sharing such characteristics are known as-

a) Group specific enzymes                                                          

b) Isoenzymes

c) Substarte specific enzymes                                                   

d) Allosteric enzymes

Q.7- Porphyrins are deposited in teeth and in bones. As a result, the teeth are reddish-brown and fluoresce on exposure to long-wave ultraviolet light, so-called ‘Erythrodontia ‘, is a sign of which porphyria?

a) Variegate porphyria                                                                  

b) Acute intermittent porphyria

c) Congenital Erythropoietic porphyria                                  

d) Hereditary Coproporphyria

Q.8- Which of the following reactions generates ATP-

a) Glucose to Glucose -6-phosphate                                      

b) Pyruvate to Lactate

c) Phosphoenol pyruvate to Pyruvate                                   

d) Glucose- 6-P to fructose-6 -P

Q.9- Formation of Galactose-1-P from Galactose is catalyzed by-

a) Hexokinase                                                                                  

b) Aldolase        

c) Galactokinase                                                                              

d) Galactose-1-P Uridyl transferase

Q.10-Which of the following is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

a) ATP                                                                                                  

b) Cu2+

c) Heme                                                                                              

d) NAD+

Q.11- Which out of the following enzymes is not TPP dependant?

a) PDH Complex                                                                                              

b) α- Keto glutarate dehydrogenase complex

c) Tryptophan pyrrolase                                                                               

d) Transaminase

Q.12- Which out of the following amino acids carries a net positive charge at the physiological p H ?

a) Valine                                                                                             

b) Leucine

c) Isoleucine                                                                                      

d) None of the followings.

Q.13- All of the followings except one are coupling agents for the detoxification of Xenobiotics-

a) Glutamic acid                                                                                               

b) Cysteine

c) Methionine                                                                                  

d) Glycine

Q.14- Which out of the followings is produced as a result of detoxification by Glycine?

a) Mercapturic acid                                                                        

b) Hippuric acid

c) Kynurenine acid                                                                          

d) Xanthurenic acid

Q.15- Which of the following is a non reducing sugar?

a) Arabinose                                                                                     

b) Trehalose

c) Erythrose                                                                                       

d) Ribulose        

Q.16- Which out of the followings is not an uncoupler of oxidative phosphorylation?

a) Atractyloside                                                                                               

b) Dicumarol

c) Thyroxin                                                                                         

d) Calcium

Q.17- Which out of the followings is not a product of tyrosine metabolism?

a) Melanin                                                                                         

b) Melatonin

c) Thyroxin                                                                                         

d) Tyramine

Q.18- Spot the inborn error whose early diagnosis is essential to avoid permanent brain damage?

a) Phenylketonuria                                                                        

b) Glycogen storage disease

c) Thalassemia                                                                                  

d) Acute Intermittent Porphyria

Q.19-Down regulation of LDL receptor occurs due to-

a) Influx of cholesterol                                                                 

b) Decreased activity of LCAT

c) Steroid synthesis                                                                        

d) Bile acid synthesis

Q.20- Which of the following hormones promotes hypoglycemia?

a) Epinephrine                                                                                 

b) Nor epinephrine

c) Glucagon                                                                                       

d) Insulin

 

Key To Answers-

1)- c, 2)-c, 3)-c, 4)- d, 5)- c, 6)- b, 7)- c, 8)-c, 9)-d, 10)-d,11)-d,12)-d,13)-a, 14)-b,15)-b,16)-a,17)-b,18)-a, 19)-a,20)-d.

 

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1) -Which of the following tests is undertaken to differentiate between Glucose and Fructose?

a) Benedict                                                                        

b) Seliwanoff

c) Molisch                                                                           

d) Osazone        

2) – Sphingosine is not present in-

a) Cerebrosides                                                               

b) Sphigomyelin

c) Gangliosides                                                                 

d) Plasmalogen

3)- Glycine and Alanine are the most abundant amino acids in the structure of-

 a) Hemoglobin                                                                                

 b) Insulin

 c) Myoglobin                                                                    

 d) Collagen

4)- Al of the following amino acids are both glucogenic as well as ketogenic except –

a) Isoleucine                                                                     

b) Tyrosine

c) Leucine                                                                           

d) Phenyl alanine

5)-A recently diagnosed hypertensive patient has been prescribed an ACE inhibitor (Angiotensin converting enzyme inhibitor) which is known to act by lowering Vmax, what is the possible mechanism of inhibition of this drug?

a) Competitive                                                                 

b) Un Competitive

c) Non Competitive                                                        

d) None of the above.

6) –Which out of the followings is not a hemo protein?

a) Tryptophan pyrrolase                                              

b) Myoglobin

c) Tyrosinase                                                                     

d) Cytochrome P450

7)-In general, the porphyrias are inherited in an autosomal dominant manner, with the exception of

a) Acute intermittent porphyria                                               

b) Variegate Porphyria

c) Porphyria Cutanea Tarda                                        

d) Congenital Erythropoietic porphyria

8)-All the following enzymes except one require NADP+ as a coenzyme-

a) Glucose- 6-phosphate dehydrogenase            

b) Malic enzyme              

c) Cytosolic Isocitrate dehydrogenase                   

d) Glucose-6-phosphatase

9) – Epinephrine is formed from nor epinephrine by-

a) Decarboxylation                                                         

b) Methylation                                                                 

c) Transamination                                                           

d) Deamination

10)- Hydrolysis of glutamine is catalyzed by-

a) Glutamate dehydrogenase                                   

b) Transaminase

c) Glutaminase                                                                 

d) None of the above

11)-Epileptiform convulsions in infants are found in the deficiency of-

a) Riboflavin                                                                      

b) Thiamine

c) Niacin                                                                              

d) Pyridoxine

12) –In the fasting state there is considerable release of———– from the muscles.

a) Glycine                                                           

b) Valine

c) Alanine                                                           

d) Glutamic acid

13)- All of the following are synthesized from Glycine except-

a) Heme                                                              

b) Creatine

c) Polyamines                                                   

d) Glutathione

14)-The Transaminase enzyme requires the presence of-

a) Inositol                                                           

b) B6

c) B12                                                                   

d) B2

15)-Which essential nutrient participates as a coenzyme in the transport of high energy electrons and H+ ions during oxidative phosphorylation in the mitochondria ?

a) Folic acid                                                        

b) Thiamine

c) Niacin                                                              

d) Ascorbic acid

16)- 5- hydroxy Indole acetic acid is the end product of which metabolite?

a) Serotonin                                                      

b) Melatonin     

c) Tyrosine                                                         

d) Histidine

17) –The coenzyme derived from Riboflavin is required by which of the following enzymes?

a) Lactate dehydrogenase                          

b) Glutamate dehydrogenase

c) Acyl co A dehydrogenase                       

d) Malate dehydrogenase

18)-Which of the following vitamins serves an antioxidant function and has a relation to selenium metabolism

a) Vitamin A                                                      

b) Vitamin C

c) Vitamin D                                                       

d) Vitamin E

19) – All of the following vitamins except one participate in the TCA cycle-

a) Pantothenic acid                                        

b) Lipoic acid

c) Folic acid                                                        

d) Riboflavin      

20) –The major metabolic product produced under normal circumstances by erythrocytes and by muscle cells during intense exercise is recycled through liver in the Cori cycle. The metabolite is-

a) Oxaloacetate                                                               

b) Alanine                                                                                          

c) Lactate                                                            

d) Glycerol

 

Key to Answers

1)-b, 2)- d, 3)- d, 4)- c, 5)- c, 6)- c, 7)- d, 8)- d, 9)- b, 10)- c, 11)- d, 12)- c, 13)- c, 14)- b, 15)- c, 16)- a, 17)- c, 18)- d, 19)- c, 20)- c.

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1)- The energy yield during the conversion of Succinate to Fumarate is-

a) 2ATP                                                                                

b) 1ATP

c) 3ATP                                                                                

d) No ATP      

2)  Which of the following occurs in non shivering thermogenesis?

a) Glucose is oxidized to lactate                                

b) Fatty acids uncouple oxidative phosphorylation

c) ATP is spent for heat production                         

d) Glycogen is excessively degraded

3) Which vitamin is required for almost all aspects of protein and amino acid metabolism?

a) Vitamin B6                                                                    

b) Vitamin B12

c) Vitamin C                                                                       

d) VitaminB3     

4) Which one of the following transfer acyl groups?   

a) Thiamine pyrophosphate                                       

b) Lipoamide

c) NADH                                                                              

d) FADH2      

5) Homocystinuria is due to the deficiency of-

a)Vitamin B12                                                                   

b) B6

c) Folic acid                                                                        

d) All of the above.

6) – Which out of the followings is not a substrate-specific enzyme?
a) Glucokinase                                                                 

b) Fructokinase

c) Hexokinase                                                                   

d) Phosphofructokinase

7) – A 67- year-old army officer in good health previously presented with sudden pain in the great toe.  Serum uric acid was high, and a diagnosis of gouty arthritis was made He was advised bed rest, pain killers and Allopurinol. What is the mechanism of action of Allopurinol in lowering serum uric acid levels?

a) Suicidal inhibition                                                       

b) Non competitive inhibition

c) Allosteric inhibition                                                    

d) Feedback inhibition

8) The mother of a mal- nourished child has been instructed to include a complete protein in the diet of her child, which out of the followings proteins should be recommended?

a) Pulses                                                                             

b) Wheat

c) Soy Protein                                                                   

d) Milk

9) Which of the following peptides is cyclic in nature-?

a) Glutathione                                                                  

b) Gramicidin-S

c) Met encephalin                                          

d) Leuencephalin

10) All the below mentioned proteins are metalloproteins except-

a) Carbonic anhydrase                                               

b) Xanthine oxidase

c) Lactate dehydrogenase                                       

d) Superoxide dismutase

11) – Which of the following supplies the 2 carbon units that are added to the elongation of fatty acid chain?

a) Acetyl co A                                                         

b) Malonyl co A

c) β- Keto acyl co A                                              

d) Glucose.

12) Glucose can be converted to glycerol-3-P through which of the following intermediates?

a) Glycerol                                                            

b) Dihydroxy acetone phosphate

c) Acetyl co A                                                       

d) Pyruvate

13) The complete oxidation of odd chain fatty acid produces which of the followings?

a) Acetyl co A only                                              

b) Acetyl co A and Propionyl co A

c) Butyryl co A                                                     

d) Palmitoyl co A

14) In which of the following porphyrias, cutaneous hypersensitivity is not observed?

a) Variegate Porphyria                                     

b) Acute intermittent Porphyria

c) Congenital Erythropoietic Porphyria         

d) Hereditary Coproporphyria

15) All are correct about pyruvate dehydrogenase complex except one-

a) The formation of acetyl CoA from pyruvate is an irreversible step

b) Pyruvate dehydrogenase is switched off when the energy charge is high

c) Phosphorylation switches off the activity of the complex.

d) Pyruvate as well as ADP (a signal of low energy charge) inhibit the complex.  

16) Which of the following is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

a) ATP

b) Cu2+

c) Heme

d) NAD+

17) The citric acid cycle is inhibited by which of the following?

a) Fluoroacetate                                                                                                                                                              

b) Aerobic conditions

c) Malic acid                                                                                                                                                                                       

d) Fluorouracil

18) Which out of the following fatty acids is a precursor of series -1 Eicosanoids?

a) Linoleic acid

b) Arachidonic acid

c) Eicosapentaenoic acid

d) Linolenic acid

19) Cholesterol is a precursor of all except-

a)Bile salts,

b)Bilirubin

c) Steroids

d) vitamin D

20) Polyamines are formed from which of the following amino acids?

a) Citrulline                                                                        

b) Ornithine

c) Arginine                                                                         

d) Argino succinic acid.

 

 

Key to answers- 1)-a,2)-b,3)-a, 4)-b,5)-d,6)-c,7)-a,8)-d,9)-b,10)-c,11)-b,12)-b,13)-b,14)-b,15)-d,16)-d,17)-a,18)-d,19)-b,20)-b

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1)- Several complexes in the electron transport chain contain non heme iron. The iron in these complexes is bound tightly to which of the following amino acids ?

a) Serine

b) Tyrosine

c) Cysteine

d) Methionine

e) Glutamine

2)- A 27 –year-old female with epilepsy has been taking Phenytoin to control her seizures. She is pregnant and considering the risk of potential bleeding episodes in the infant, her physician is considering to change her medicine. What biochemical activity might be deficient in the baby if her medication is continued as such?

a) Hydroxylation of proline

b) Gamma carboxylation of glutamic acid residues

c) Glucuronidation of bilirubin

d) Oxidation of lysine

e) Oxidation of glutathione.

3)- A 75-year-old female is seen in the emergency room with fractured arm. Physical examination reveals multiple bruises, perifollicular hemorrhages and bleeding gums. Her diet consisted mainly of plain buns, pasta, rolls and coffee. Laboratory result indicates Microcytic hypochromic anemia. Which of the following enzymes should be less active than the normal in this patient?

a) Glutathione peroxidase

b) Prolyl hydroxylase

c) Gamma Glutamyl transferase

d) ALA synthase

e) Glutathione reductase

4)- An 8-year-old child of IDDM (Insulin dependent diabetes mellitus) has been brought to emergency in a semi conscious state. History reveals that he had flu like episode 8 days back. His breathing is rapid and his breath has a fruity odor. His blood glucose is 345 mg/dl. The physician has started with I/V fluids, Insulin and potassium chloride. Insulin under such condition would rapidly stimulate which of the following processes-

a) Gluconeogenesis in liver

b) Glycogenolysis in liver

c) Uptake of glucose in peripheral cells

d) Lipolysis in adipose tissue

e) Ketone body utilization in brain cells.

5)- A 55-year-old chronic alcoholic was brought to emergency by his friends. During their night time gathering in the local bar he fell unconscious and they had been unable to revive him. The attending physician ordered for I/V Glucose and an injection of Thiamine. The patient was well oriented and alert next morning,  his vital signs were stable, blood glucose was normal and he was discharged from the hospital. Which of the following enzymes is thiamine dependent and vital for glucose oxidation in brain?

a) Transketolase

b) Transaldolase

c) Transaminase

d) Pyruvate dehydrogenase complex

e) Alpha keto acid dehydrogenase complex

6)- During acute myocardial infarction, the oxygen supply to an area of heart is reduced forcing the cardiac muscle cells to switch to anaerobic oxidation. Under this conditions the activity of which of the following enzymes is increased by the increasing concentration of AMP?

a) Phospho fructo kinase-1

b) Pyruvate kinase

c) Citrate synthase

d) Lactate dehydrogenase

e) Succinate dehydrogenase

7)- A 50- year-old male is seen in the emergency with severe headache. His blood pressure is 210/130 mm Hg. An evidence of retinal hemorrhage and epistaxis is also there. He has been given an infusion of nitroprusside. Which of the following enzymes  is directly affected by the active metabolite of this drug ?

a) Phospholipase A2

b) Phospholipase C

c) Guanylate cyclase

d) Phosphodiesterase

e)  Adenylate cyclase

8) A 16-month-old girl was found to have ingested approximately 30 mL of an acetonitrile-based cosmetic nail remover when she vomited 15 minutes post ingestion  The poison control center was contacted, but no treatment was recommended because it was confused with an acetone-based nail polish remover. The child was put to bed at her normal time, which was 2 hours post-ingestion  Respiratory distress developed sometime after the child was put to bed, and she was found dead the next morning.

Inhibition of which of the following enzymes was the most likely cause of this child’s death?

a) Cytochrome c reductase

b) Cytochrome oxidase

c) Coenzyme Q reductase

d) NADH dehydrogenase

e) Succinate dehydrogenase

9)- Excess of nitroprusside sometimes causes cyanide toxicity and is treated by giving thiosulfate, Which complex associated with electron transport chain or oxidative phosphorylation gets inhibited by the toxic metabolic product of nitroprusside?

a) ATP synthase complex

b) Succinate dehydrogenase complex

c) ADP/ATP transporter

d) NADH dehydrogenase complex

e) Cytochrome a-a3 oxidase

10)-A patient has been exposed to toxic compound that increases the permeability of mitochondrial membrane for protons. Which of the following will not be observed in the liver cells ?

a) Increased glycolysis

b) Increased activity of ATP synthase complex

c) Increased concentration of ADP

d) Increased activity of PFK-1

e) Increased activity of pyruvate kinase

11) – A 56-year-old man with a history of genetic disease underwent hip replacement surgery for arthritis. During surgery black stains were observed in the cartilage. These stains are usually observed in patients suffering from Ochronosis, a condition initially characterized by darkening of urine upon standing (Alkaptonuria). There is deficiency of Homogentisic acid oxidase in this condition. Which of the following vitamins acts as a coenzyme for the above said enzyme ?

a) Vitamin B12

b) Folic acid

c) Ascorbic acid

d) Niacin

e) Riboflavin

12)  In a  patient with Abetalipoproteinemia,  abnormal red blood cells (Acanthocytes- thorny looking cells) are observed, there is defective synthesis of Apo B protein in this condition. Which of the following would have impaired absorption, the deficiency of which leads to impaired membrane formation in this condition  ?

a) Folic acid

b) Ascorbic acid

c) Palmitic acid

d) Arachidonic acid

e) Linolenic acid

13) Failure of down regulation of extra hepatic receptors for oxidized LDL is mainly responsible for the formation of foam cells and for triggering the process of atherosclerosis. This process can be prevented  by timely supplementation of antioxidants. Which of the following should be considered the best choice  to be considered as an antioxidant ?

a) Vitamin B6

b) Vitamin K

c) Vitamin D

d) Vitamin E

e) Folic acid

14)- A factory worker is on hunger strike from the last 3 days. Beta oxidation is presumed to be highly active, under such condition. What would be the expected fate of mitochondrial pyruvate  ?

a)  Oxidatively decarboxylated to form Acetyl co A to be used in TCA cycle

b) Carboxylated to Phosphoenol pyruvate  to be used for gluconeogenesis

c) Reduced to lactate to be used for gluconeogenesis

d) Oxidatively decarboxylated to form Acetyl co A to be used for ketogenesis

e) Carboxylated to Oxalo acetate  to be used for gluconeogenesis.

15) -In the fed state after a very heavy meal, there is active lipogenesis in the adipose tissue. Glycolysis must go on at the same pace to provide which of the following intermediate from glycolysis required for fat storage ?

a) Acetyl co A

b) Pyruvate

c) Glucose-6-P

d) Glycerol

e) Dihydroxy acetone phosphate

16) A child is diagnosed with  congenital deficiency of medium chain Acyl co A dehydrogenase. Which of the following biochemical finding would be observed in the fasting state ?

a) Hyperglycemia

b) Low blood lactate level

c) Ketosis

d) Dicarboxylic acidosis

e) Alkalosis

17)  A 6-year-old child has been  brought with impairment of vision. He is diagnosed  with Galactosemia.  Which enzyme is responsible for causing premature cataract in such affected children ?

a) Sorbitol dehydrogenase

b) Aldose reductase

c) Galactokinase

d) Galactose-1-P- Uridyl transferase

e) Aldolase -B

Key to Answers-

1)- c, 2)- b, 3)- b, 4)- c, 5)- d, 6)- a, 7)-c, 8)- b, 9)- e, 10)- b, 11)- c, 12)- d, 13)-d, 14)- e,  15)-e, 16)-d, 17)-b.

 

 

 

 

 

 

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Q.-1- All amino acids except one participate in phase 2 reactions of detoxification
a) Serine
b) Glycine
c) Glutamine
d) Cysteine
(a)
Q.2- Which out of the following pathways helps in reductive biosynthesis
a) Uronic acid pathway
b) HMP pathway
c) Glycolysis
d) All of the above
(b)
Q.3- All of the following clinical manifestations except one are present in hemochromatosis-
a) Bronze discoloration of skin
b) Diabetes mellitus
c) Iron overload
d) Hemolytic anemia
(d)
Q.4- A person on ingestion of Primaquine develops hemolytic anemia, what is the possible defect?
a) Deficiency of Iron
b) Vitamin K deficiency
c) Glucose-6-P dehydrogenase deficiency
d) Vitamin C deficiency
(c)
Q.5- The enzyme responsible for conversion of Biliverdin to Bilirubin is-
a) Bilirubin esterase
b) Bilirubin oxidase
c) Glucuronyl transferase
d) Biliverdin reductase
(d)
Q.6-Biotin is involved in which of the following types of reactions-
a) Deamination
b) Decarboxylation
c) Carboxylation
d) Transamination
(c)
Q.7-The Xanthurenic acid test (Xanthurenic index) can be used to measure pyridoxine deficiency, it involves the metabolism of-
a) Glycine
b) Histidine
c) Tryptophan
d) Tyrosine
(c)
Q.8-McArdle’s disease is characterized by the deficiency of-
a) Muscle phosphorylase
b) Liver phosphorylase
c) Glucose-6-phosphatse
d) Phosphofructokinase
(a)
 Q.9-Out of 24 mols of ATP formed in citric acid cycle, 2 mols of ATP can be formed at substrate level by which of the following reaction?
a) Citrate——> Isocitrate
b) Isocitrate——–>Oxalo succinate
c) Succinate——->  Fumarate
d)Succinyl co A–> Succinate
(d)
 Q.10- All of the following metabolic abnormalities are observed in Diabetes mellitus, except-
a) Increase plasma free fatty acids
b) Increased pyruvate carboxylase activity
c) Decreased PDH complex activity
d) Increased lipoprotein lipase activity
(d)

Q.11-Beta oxidation of odd chain fatty acids yields

a) Succinyl co A
b) Propionyl co A
c) Acetoacetyl co A
d) Dicarboxylic acids
(b)
 Q.12-Iron therapy is ineffective in which of the following conditions-
a) Chronic blood loss
b) Inadequate iron intake
c) Thalassemia major
d)Acute blood loss
(c)
Q.13-Which of the following vitamins is not a component of electron transport chain-
a) Nicotinamide
b) Ubiquinone
c) Biotin
d) Riboflavin
(c)
Q.14-Which of the following enzymes does not have an impaired activity in Vitamin B1 deficiency?
a) Succinatedehydrogenase
b) Pyruvate dehydrogenase
c) Transketolase
d) Alpha keto glutarate dehydrogenase
(a)
Q.15- Considering the citric acid cycle steps between alpha keto glutarate and Malate, how many high-energy phosphate bonds or net ATP molecules can be generated?
a) 5
b) 6
c) 8
d) 10
(b)
Q.16- The standard free energy change (in terms of net ATP production) when glucose is converted to 6CO2 and 6H2O is about how many times as great as the free energy change when glucose is converted to  two lactate molecules ?
a) 2
b) 4
c) 19
d) 10
(c)
Q.17- The rate of flow of electrons through the electron transport chain is regulated by
a)ATP:ADP ratio
b) Concentration of Acetyl co A
c) Feed back inhibition by H2O
d) Catalytic rate of cytochrome oxidase
(a)
 Q.18- The major product of fatty acid synthase complex is-
a) Oleate
b) Palmitate
c) Palmityl co A
d) Stearoyl co A
(b)
Q.19- The primary enzyme for utilization of ketone bodies is-
a) Thiokinase
b) Thioesterase
c) Thiophorase
d) Thiolase
(c)
Q.20-All of the following processes except one are mitochondrial-
a) Glycolysis
b) TCA cycle
c) Beta oxidation of fatty acids
d) Ketogenesis
(a)
Please help "Biochemistry for Medics" by CLICKING ON THE ADVERTISEMENTS above!


Q.-1- All amino acids except one participate in phase 2 reactions of detoxification-
a) Serine
b) Glycine
c) Glutamine
d) Cysteine
Q.2- Which out of the following pathways helps in reductive biosynthesis-
a) Uronic acid pathway
b) HMP pathway
c) Glycolysis
d) All of the above
Q.3- All of the following clinical manifestations except one are present in hemochromatosis-
a) Bronze discoloration of skin
b) Diabetes mellitus
c) Iron overload
d) Hemolytic anemia
Q.4-A person on ingestion of Primaquine develops hemolytic anemia, what is the possible defect?
a) Deficiency of Iron
b) Vitamin K deficiency
c) Glucose-6-P dehydrogenase deficiency
d) Vitamin C deficiency
Q.5- The enzyme responsible for conversion of Biliverdin to Bilirubin is-
a) Bilirubin esterase
b) Bilirubin oxidase
c) Glucuronyl transferase
d) Biliverdin reductase
Q.6-Biotin is involved in which of the following types of reactions-
a) Deamination
b) Decarboxylation
c) Carboxylation
d) Transamination
Q.7-The Xanthurenic acid test (Xanthurenic index) can be used to measure pyridoxine deficiency, it involves the metabolism of-
a) Glycine
b) Histidine
c) Tryptophan
d) Tyrosine
Q.8-McArdle’s disease is characterized by the deficiency of-
a) Muscle phosphorylase
b) Liver phosphorylase
c) Glucose-6-phosphatse
d) Phosphofructokinase
Q.9-Out of 24 mols of ATP formed in citric acid cycle, 2 mols of ATP can be formed at substrate level by which of the following reaction?
a) Citrate————-> Isocitrate
b) Isocitrate———-> Oxalo succinate
c) Succinate———> Fumarate
d) Succinyl co A—–> Succinate
Q.10- All of the following metabolic abnormalities are observed in Diabetes mellitus, except-
a) Increase plasma free fatty acids
b) Increased pyruvate carboxylase activity
c) Decreased PDH complex activity
d) Increased lipoprotein lipase activity
Q.11-Beta oxidation of odd chain fatty acids yields-
a) Succinyl co A
b) Propionyl co A
c) Acetoacetyl co A
d) Dicarboxylic acids
Q.12-Iron therapy is in effective in which of the following conditions-
a) Chronic blood loss
b) Inadequate iron intake
c) Thalassemia major
d)Acute blood loss
Q.13-Which of the following vitamins is not a component of electron transport chain-
a) Nicotinamide
b) Ubiquinone
c) Biotin
d) Riboflavin
Q.14-Which of the following enzymes does not have an impaired activity in Vitamin B1 deficiency?
a) Succinate dehydrogenase
b) Pyruvate dehydrogenase
c) Transketolase
d) Alpha keto glutarate dehydrogenase
Q.15- Considering the citric acid cycle steps between alpha keto glutarate and Malate, how many high-energy phosphate bonds or net ATP molecules can be generated?
a) 5
b) 6
c) 8
d) 10
Q.16- The standard free energy change (in terms of net ATP production) when glucose is converted to 6CO2 and 6H2O is about how many times as great as the free energy change when glucose is converted to  two lactate molecules ?
a) 2
b) 4
c) 19
d) 10
Q.17- The rate of flow of electrons through the electron transport chain is regulated by
a) ATP:ADP ratio
b) Concentration of Acetyl co A
c) Feed back inhibition by H2O
d) Catalytic rate of cytochrome oxidase
Q.18- The major product of fatty acid synthase complex is-
a) Oleate
b) Palmitate
c) Palmityl co A
d) Stearoyl co A
Q.19- The primary enzyme for utilization of ketone bodies is-
a) Thiokinase
b) Thioesterase
c) Thiophorase
d) Thiolase
Q.20-All of the following processes except one are mitochondrial-
a) Glycolysis
b) TCA cycle
c) Beta oxidation of fatty acids
d) Ketogenesis
Please help "Biochemistry for Medics" by CLICKING ON THE ADVERTISEMENTS above!

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