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Case Studies

1) 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

Answer- 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. Glucocorticoids 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.

2) 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

d) Calcitonin

e) Prolactin

Answer- The right answer is-d)- 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

3) 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

Answer- 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 .

4) 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

Answer- 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.

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1) 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

2) 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

d) Calcitonin

e) Prolactin

3) 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

4) 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

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A 20 year-old- male has presented with intermittent ataxia (abnormal gait), paralysis of eye muscles, and confusion.  Blood glucose  has been found to be 52 mg/dl  but there are no ketone bodies in urine. 

After an extensive work up, he has been diagnosed with Carnitine acyl transferase I (CAT-I) deficiency. The reaction catalyzed by CAT-I forms-

A) Fatty acyl co A

B) Fatty acyl Carnitine

C) Malonyl co A

D) Palmitoyl co A

E) Carnitine

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The right answer is – D and E) Porphobilinogen synthase also called 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). 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 (See figure)

C) ALA synthase is the first  enzyme of heme bio synthetic pathway, that catalyzes the condensation of Glycine and Succinyl co A (See figure)

lead

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure- showing steps of heme biosynthesis and the inhibition of ALA dehydratase and ferrochelatase  by lead.

For further details follow the link-

 

http://www.namrata.co/case-study-porphyria/

 

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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 that the child belongs to a very poor family, 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) Porphobilinogen synthase

E) ALA dehydratase

lead paint

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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 Kinase

D) Alpha keto glutarate dehydrogenase

E) Succinate dehydrogenase

Answer-  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 (Figure-1) 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 keto acid dehydrogenase complex. The later enzymes is involved in the metabolism of branched chain amino acids. In the presence of Arsenite, 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.

1

Figure-1- showing structure of lipoic acid

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 (Figure-2).Thus by bypassing the synthesis and dephosphorylation of 1,3 BPG, the cell is deprived of energy usually obtained from Glycolysis.

2

Figure-2- Arsenate competes with inorganic phosphate forming 1-Arseno-3- phosphoglycerate that spontaneously hydrolyzes forming 3-phosphoglycerate, thus no ATP is formed by substrate level phosphorylation in Glycolysis.

Arsenic  also competes with phosphates for adenosine triphosphate, forming adenosine diphosphate mono arsine, 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 although are enzymes of TCA 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 but are not widely proved.

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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 Kinase

D) Alpha keto glutarate dehydrogenase

E) Succinate dehydrogenase

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During an extended period of exercise, the enzymes involved in the glycolytic pathway in muscle tissue actively break down glucose to provide the muscle energy. The liver, to maintain blood glucose levels, synthesizes 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

miche

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During starvation muscle activity decreases, and muscle protein is broken down to provide a carbon source for the liver production of glucose via gluconeogenesis. Which of the following amino acids remains in the muscle cell to provide a source of energy for the muscle?

A. Alanine

B. Aspartate

C. Leucine

D. Glutamate

E. Threonine

starvation-topic-1

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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

cataract

 

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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

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An underweight  4 -year-old boy  was brought to the emergency in a semi conscious state. His blood glucose, urea and glutamine were abnormally low, acetoacetate was elevated but lactate was normal. He was admitted to I.C.U. where his blood glucose was increased  by injection glucagon. Which metabolic pathway is most likely deficient in this child ?

A) Hepatic gluconeogenesis

B) Skeletal muscle glycogenolysis

C) Adipose tissue lipolysis

D) Skeletal muscle proteolysis

E) Hepatic glycogenolysis

HYPO

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