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Viva

1) Name the pathways that can utilize Glucose-6-P as a substrate.

2) What is the net energy output when the R/L shunt is active in the red blood cells?

3) Name an enzyme that uses inorganic phosphate for the phosphorylation of the substrate.

4) How is excessive fructose consumption related to obesity?

5) Why do sucrase and isomaltose deficiencies coexist?

6) Which pathway of glucose utilization is concerned with the production of ribose?

7) What is the biochemical basis of mental retardation in classical galactosemia?

8) What is the purpose of branching in glycogen structure?         

9) Glucose-6-P dehydrogenase deficiency primarily affects the red blood cells, why are the other cells of the body not affected by this deficiency?

10) Name the important inhibitors of glycolysis.

11) What is the significance of rising concentration of glucose-6-P on phosphorylase enzyme?

12) What is the normal range of blood glucose level?

13) Give example of substrate level phosphorylation in TCA cycle.

14) What is mechanism of inhibition of Aconitase enzyme by fluoroacetate?

15) How do odd chain fatty acids which are considered to be glucogenic gain entry in to the main pathway?

16) What is the major outcome of uronic acid pathway?

17) How many ATP molecules are produced when glucose is completely oxidized in skeletal muscle under aerobic conditions?

18) Name the key regulatory enzyme of glycogen synthesis.

19) How do skeletal muscles contribute towards maintenance of blood glucose level?

20) What is the cause of lactic acidosis in PDH complex deficiency?

21) The skeletal muscles are deficient in glucose-6-P dehydrogenase enzyme, how do they manage to synthesize ribose?

22) Name the concerned pathway for each of the following enzymes

a) Transaldolase

b) Phosphofructokinase-2

c) UDP-G pyro phosphorylase

d) Debranching enzyme

e) Aldolase B

23) Mention the role of 2,3 BPG in unloading of oxygen in a fetus ?

24) State the inhibitor of each of the following enzymes

a) Succinate dehydrogenase

b) Lactate dehydrogenase

c) Pyruvate dehydrogenase

d) Phospho triose isomerase

e) Enolase

25) Name the allosteric modifiers (negative and positive) for each of the following enzymes-

a) PFK-1

b) Fructose 1,6 bisphosphatase

c) Glycogen synthase

d) Phosphorylase

e) Pyruvate kinase

26) Name the enzyme catalyzing the following biochemical reactions-

a) Lactate to Pyruvate

b) Malate to oxaloacetate

c) Pyruvate to Alanine

d) Glucose-6-P to Fructose-6-P

e) Glyceraldehyde-3-P to Dihydroxyacetone –P

27) “Muscle glycogen phosphorylase is non responsive to glucagon”, what is the reason?

28) Phosphorylase enzyme is active in the dephosphorylated form, is it true or false?

29) What are the major tissues for gluconeogenesis?

30) Name the coenzyme for pyruvate carboxylase enzyme .

Note- Students should refer theory notes or subjective questions of carbohydrate metabolism for getting the answers.

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1. What are the components of PDH(Pyruvate dehydrogenase) complex?

Answer-

Enzymes

a) Pyruvate dehydrogenase

b) Dihydro lipoyl transacetylase

c) Dihydrolipoyl dehydrogenase

d) PDH kinase

e) Phosphatase

Coenzymes- Thiamine pyro phosphate (TPP), Co ASH, Lipoic acid, FAD and NAD+

2- What is the biological role of Oxalo acetate?

Answer- Oxalo acetate is required for the functioning of TCA cycle; for the synthesis of glucose ; for the synthesis of Aspartate and Asparagine.

3- What is the fate of pyruvate under different conditions?

Answer- The main fate is conversion to Acetyl co A. Depending upon cellular needs and the availability of oxygen it can be converted to lactate, alanine, oxalo acetate, malate or ethanol (in micro organisms).

4- What is Pasteur Effect?

Answer- The inhibition of glycolysis upon oxygen administration when the glucose was previously getting oxidized under anaerobic condition is called Pasteur Effect.

Biochemical basis-Glycolysis occurs at a higher rate during anaerobic conditions. Hypoxia stimulates glycolysis. Upon oxygen administration, the conditions change from anaerobic to aerobic, there is more ATP formation. ATP is a negative allosteric modifier of PFK-1, the key regulatory enzyme of glycolysis. Inhibition of PFK-1 causes inhibition of glycolysis.

5- In which of the organs of the body, maximum amount of glycogen is stored?

Answer- Glycogen occurs mainly in liver and muscle; although the liver content of glycogen is greater than that of muscle, because the muscle mass of the body is considerably greater than that of the liver, about three-quarters of total body glycogen is in muscle

6- Name the key regulatory enzyme of glycolysis?

Answer- Phospho-fructo kinase-1 (PFK-1) is the key regulatory enzyme of glycolysis.

6- Which pathway is maximally active in the fed state (Glycogenesis /glycogenolysis)?

Answer- Glycogenesis occurs maximally in the fed state under the effect of insulin.

7- What is the biochemical defect in hereditary fructose intolerance?

Answer- Deficiency of Aldolase B enzyme

8- Why is it inappropriate to say that “Fats can not be converted to glucose?”

Answer- Glycerol and odd chain fatty acids are glucogenic. It is only Acetyl co A , the product of oxidation of even chain fatty acids that  is not glucogenic. Thus it is not appropriate to say that fats can not be converted to glucose.

9-Out of Glucokinase and hexokinase which of the enzymes is inducible in nature?

Answer- Glucokinase is inducible in nature.

10- Which type of the glucose transporters are under the control of insulin?

Answer-Only GLUT-4 transporters, present in skeletal muscle and adipose tissue are insulin dependent.

11- Enumerate the sources of NADPH.

Answer- NADPH can be produced from-

a) HMP shunt pathway

b) By the activity of cytosolic isocitrate dehydrogenase and

c) By the activity of Malic enzyme.

12- Which reaction is catalyzed by Glucose-6-P dehydrogenase?

Answer- Glucose-6-P dehydrogenase catalyzes the conversion of glucose-6-P to 6-Phosphogluconolactone.

13- What is the effect of rising concentration of AMP on glycolysis?

Answer- Rising concentration of AMP is a sign of low energy state of the cell. AMP acts as a positive allosteric modifier for PFK-1 enzyme. The enzyme gets stimulated to activate the pathway.

14- What is the effect of rising concentration of citrate on PFK-1?

Answer- Citrate is a negative allosteric modifier of PFK-1. Reduced activity of PFK-1 in the presence of high concentration of citrate results in inhibition of glycolytic pathway

15- Which reaction is catalyzed by lactate dehydrogenase enzyme?

Answer- Lactate dehydrogenase causes interconversion of pyruvate and lactate.

16- Name the pathways of glucose utilization in red blood cells?

Answer- Glucose is utilized through glycolysis and HMP pathway in red blood cells.

17- What is the cause of positive Benedict’s test in essential Pentosuria?

Answer- Excess excretion of L- Xylulose, which is reducing in nature, gives a positive reaction with Benedict’s reagent in essential Pentosuria.

18- Out of Transaldolase and transketolase which of these two enzymes is TPP dependent?

Answer- Transketolase, an enzyme of HMP pathway is TPP dependent.

19- Name the coenzymes needed for the functioning of Alpha keto glutarate dehydrogenase complex?

Answer- The coenzymes are same as PDH complex, and these are -Thiamine pyro phosphate (TPP), Co ASH, Lipoic acid, FAD and NAD+.

20- What is the cause of premature cataract in classical galactosemia?

Answer- In classical galactosemia,  excess of unutized galactose is reduced to galacitol which is osmotically  active to cause opacification of lens to cause cataract.

 

 

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1- What is the commonest mode of absorption of fructose?

Answer- Facilitated transport through GLUT-5.

2- What is the biochemical defect is classical galactosemia?

Answer- Deficiency of Galactose- 1-P Uridyl transferase

3-In which of the pathways of glucose utilization, CO2 is not evolved?

Answer- Glycolysis

4- What is the cause of hemolysis in Pyruvate kinase deficiency?

Answer- Energy deficit, improper functioning of Na-K  ATPase pump, retention of Sodium in the cell, osmolysis.

5- What is the reason that ascorbic acid can not be synthesized by human beings whereas it can well be synthesized by plants and certain animals?

 Answer- Deficiency of gulonolactone oxidase enzyme.

6- Name the precipitating factors for causing symptoms of Glucose-6-P dehydrogenase deficiency.

Answer- Drugs (Analgesics/ Antipyretics, antibiotics and antimalarials), infections and ingestion of fava beans.

7- Which reaction is catalyzed by Aldolase B enzyme?

Answer-  It is an enzyme of fructose metabolism causes cleavage of Fructose-1-P to form glyceraldehyde and dihydroxy acetone phosphate.

8- What is the point of entry of glycerol in the pathway of gluconeogenesis?

Answer- Glycerol  is  first phosphorylated to form Glycerol-3-P, that gets converted to dihydroxy acetone phosphate to gain entry in to the pathway of gluconeogenesis.

9- What are the sources of Acetyl co A?

Answer- Acetyl co A is mainly produced from pyruvate, fatty acid oxidation, ketolysis, alcohol metabolism and from ketogenic amino acids.

10- What is the main significance of Fructose 2, 6 bisphosphate?

 Answer- It acts as a positive allosteric modifier for PFK-1 enzyme. The whole pathway is thus stimulated.

11- What is the end product of glycolysis in red blood cells?

Answer- Lactate.

12- How many ATP s are produced from one molecule of glucose upon complete oxidation in red blood cells?

Answer- 2 ATPs

13- Name the pyruvate forming amino acids.

Answer- Glycine, alanine, serine, tryptophan, threonine and cysteine.

14- What is the reason that Acetyl co A is not considered glucogenic?

Answer- Firstly the reaction from Pyruvate to Acetyl coA is irreversible, secondly in TCA cycle Acetyl co A loses both its carbons as CO2 , hence nothing is left for glucose production.

15- What is the cause of abdominal distension and diarrhea in lactose intolerance?

Answer- Undigested lactose undergoes bacterial fermentation to produce gases (a mixture of hydrogen, carbon dioxide, and methane).The osmotic load of the unabsorbed lactose causes secretion of fluid and electrolytes until osmotic equilibrium is reached. The combined increase in fecal water, intestinal transit, and generated hydrogen gas accounts for the wide range of gastrointestinal symptoms.

16- Out of Hexokinase and Glucokinase which of the enzymes has larger km?

Answer- Glucokinase has a larger km than hexokinase.

17- Name the key enzyme for glycogen degradation?

Answer- Phosphorylase.

18- What is the cause of hypoglycemia upon chronic alcohol intake?

Answer- Chronic alcohol consumption causes hypoglycemia due to-

a) Dietary deprivation

b) Depletion of glycogen stores

c) Inhibition of gluconeogenesis (Alcohol metabolism results in accumulation of NADH , the equilibrium of the reactions requiring this coenzyme is favored towards utilization of NADH, thus pyruvate and oxaloacetate are converted to lactate and malate respectively, in the deficiency of substrates, the pathway of gluconeogenesis is inhibited. )

19- Out of insulin and glucagon which of these two hormones promotes glycogenolysis?

Answer- Glucagon

20- Name the confirmatory tests for Essential Pentosuria?

Answer- Bial’s test and chromatography.

Note- Students should consult the theory notes or subjective questions for further details.

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