Monday, August 27, 2012

Glycogen Metabolism- Multiple Choice Questions

1) An infant presents with an enlarged heart, muscle weakness, and hypoventilation. She is diagnosed with glycogen storage disease type II, a disease-causing, abnormal glycogen storage in the heart, skeletal muscle and respiratory muscles. Glycogen synthase is the regulatory enzyme for glycogen synthesis. It adds glucose residues to the nonreducing ends of a glycogen primer from:
a) Glucose-1-P
b) Glucose-6-P
c) UDP- Glucose
d) UTP
e) ATP.
2) A 30- year-old male presents with severe muscle cramps. He is found to have muscle glycogen phosphorylase deficiency(Mc Ardle’s disease, Glycogen storage type 5).Glycogen phosphorylase degrades glycogen to produce-
a) Glucose
b) Glucose-1-P
c) Glucose-6-P
d) UDP Glucose
e) Glycogen Primer
3) A 15-year-old type 1 diabetic faints after injecting himself with insulin. He is administered Glucagon and rapidly recovers consciousness. Glucagon induces activity of:
a) Glycogen synthase
b) Glycogen phosphorylase
c) Glucokinase
d) Hexokinase
e) UDP Glucose pyrophosphorylase.
4) A 30-year-old presents with intractable vomiting and inability to eat or drink for the past 3 days. His blood glucose level is normal. Which of the following is most important for maintenance of blood glucose ?
a) Liver
b) Heart
c) Skeletal muscle
d) Lysosome
e) Spleen.
5) Shortly after birth, an infant presents with tremors, irritability and seizures. His blood glucose is profoundly low, and he is fed through a nasogastric tube. he is diagnosed with glycogen storage disease type I, a disease that causes excessive build up of liver glycogen, resulting in abnormally low blood glucose level. In glycogen, the linkage at branch points is:
a) α -1,4
b) α-2,3
c) α-1,6
d) β-1,4
e) β-2,3.
6) A 15-year-old male presents with increased thirst, hunger, urination, and weight loss. His fasting blood glucose level is 400 mg/dl and is diagnosed with type 1 diabetes mellitus. What is the reason for this patient’s inability to maintain a normal blood glucose level ?
a) Decreased uptake of glucose by peripheral cells
b) Abnormal response to glucagon
c) Decreased glucagon to insulin ratio
d) Decreased glucose output by the liver
e) Increased ketone body production.
7) Which enzyme is not present in muscle ?
a) Phosphorylase b
b) Hexokinase
c) Glucose-6-phosphatase
d) Glycogen synthase
e) Lactate dehydrogenase
8) Glycogenolysis is best described by which of the following statements ?
a) It involves enzymes cleaving β, 1-4 glycosidic linkage
b) Requires activation of glycogen synthase
c) Requires a dual action enzyme α-1,4 glycosidase and transferase
d) Uses ATP to produce glucose-1-P
e) Requires inactivation of phosphorylase kinase.
9) Glycogenesis from Glucose-1-P requires which of the followings ?
a) Phosphoglucomutase
b) Uridine triphosphate (UTP)
c) α-1,6 glucosidase
d) Glycogen primer
e) Uridine diphosphate
10) In glycogen, glucose residues form a straight chain via which of the followings-
a) α -1,4 linkages
b) α -1,6 linkages
c) α -1,4 linkages with glycogenin at the non reducing end
d) α -1,6 linkages with UDP glucose at any end
e) straight chain occurs at 3 residues apart
11) In the liver Epinephrine induced glycogenolysis :
a) Requires UDP glucose pyrophosphorylase
b) Requires Phosphoglucomutase
c)Requires inactivation of phosphorylase a
d) Inhibited by c AMP
e) acts upon both liver and muscle cells, similar to glucagon.
12) Glycogen catabolism is best described by which of the following statements-
a) In the brain, it yields glucose for skeletal muscle consumption
b) It requires a debranching enzyme in the erythrocytes
c) It is not a major pathway in the brain
d) It uses phosphorylase for glucose residue cleavage from the reducing end of glycogen in liver
e) It is stimulated by Insulin in liver.
13) During the breakdown of glycogen, free glucose is formed from which of the following ?
a) Glucose residues in α-1,4 glycosidic linkages
b) The reducing end
c) The non reducing end
d) Glucose residues in α-1,6 glycosidic linkages
e) Hydrolysis of glucose-1-P
14) Which of the following statements explains the synthesis of glycogen directly from D- Glucose ?
a) It does not use glucose-1-P
b) It requires a debranching enzyme
c) It occurs in erythrocytes.
d) It requires UDP-Glucose
e) It requires a glucosyl transferase
15)The degradation of glycogen normally produces which of the followings ?
a) More glucose than Glucose-1-P
b) More Glucose-1-P than Glucose
c) Equal amount of Glucose and Glucose-1-P
d) Neither Glucose nor Glucose-1-P
e) Only Glucose-I-P
16) Which of the following statements about liver phosphorylase kinase is most accurate ?
a) It is present in the inactivated form when epinephrine is released
b) It phosphorylates phosphorylase to make it inactive
c) It is stimulated by c AMP mediated phosphorylation cascade
d) It is not affected by ATP
e) It is phosphorylated in response to Insulin.
17) A newborn is found to have fasting hypoglycemia. The nursery staff begins overnight feeds by nasogastric tube because they find that the child consistently has low blood glucose. A liver biopsy and molecular studies demonstrate an absence of Glycogen synthetase. The normal function of this enzyme is to do which of the followings ?
a) Remove glucose residues one at a time from glycogen in liver
b) Remove glucose residues one at a time from glycogen in muscles
c) Transfer UDP glucose to the non reducing end of glycogen primer
d) Hydrolyze α-1,6 bonds of glycogen
e) Function as a glucosyl 4:6 transferase.
18) A 3-year-old child presents to the pediatrician for failure to thrive. A workup including an ultrasound of his liver shows cirrhosis. A biopsy of liver demonstrates a deficiency of an enzyme involved in glycogen synthesis. Which of the following is the most likely glycogen storage disease ?
a) Type I -Von Gierke’s disease
b)Type II – Pompe’s disease
c) Type III- Cori’s disease
d) Type IV- Andersen’s disease
e) Type V- McArdle disease
19) A new-born is experiencing failure to thrive. On physical examination, organomegaly is appreciated due to accumulation of glycogen in the lysosomes of several organs, including the heart, muscle and liver. A diagnosis of Pompe’s disease is made. Which of the following biochemical deficits are seen in this disorder ?
a) Glycogenin deficiency
b) An α-1,6 glycosidase deficiency
c) A glucose-6-phosphatase deficiency
d) A glycogen phosphorylase deficiency
e) A lysosomal glucosidase deficiency
20) A second year medical student decides to do research in a nutrition laboratory that is studying the effect of caffeine on cellular metabolism. Caffeine inhibits cAMP phosphodiesterase. If caffeine is added to cells, which of the following enzymes is phosphorylated and inactivated in liver ?
a) Phosphorylase kinase
b) Calmodulin
c) Phosphorylase
d) Protein kinase A
e) Glycogen synthase
21) A 28-year-old professional cyclist has been training for an opportunity to go for a long race. His coach strongly suggests the intake of carbohydrates after the work out to ensure a muscle glycogen storage that can endure the 28-day race. The activity of muscle glycogen synthase in resting muscles is increased by the action of which of the followings?
b) Glucagon
c) Insulin
d) Phosphorylation
e) Fasting and starvation.
22) An infant was brought in to the emergency room after her parents witnessed her having a seizures. The child’s blood glucose was 28mmol/L. After a thorough workup, a GSD was suspected, and a muscle biopsy was significant for the accumulation of dextrin, a form of glycogen with branching limited to only a few glucose molecules. Which of the following GSD is most likely the cause of hypoglycemia and subsequent seizures ?
a) Type I -Von Gierke’s disease
b)Type II – Pompe’s disease
c) Type III- Cori’s disease
d) Type IV- Andersen’s disease
e) Type V- McArdle disease

Answers- 1) c, 2)-b, 3)-b, 4)-a, 5)-c, 6)-a, 7)-c, 8)-c, 9)-d 10)-a
11)-b, 12)-c, 13)-d, 14)-d, 15)-b, 16)-c, 17)-c, 18)-d, 19)-e, 20)-e,
21)-c, 22)-c.

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