Biochemistry Questions on “Coordinated Regulation of Glycogen Synthesis and Breakdown”.
1. Glucagon and epinephrine stimulate glycogen breakdown to glucose 6-phosphate ________
A. Directly by binding to glycogen phosphorylase
B. Indirectly by first stimulating adenylate cyclase to make cAMP
C. Only in the liver
D. Only in muscle cells
Answer: B
Clarification: The second messenger cAMP increases in concentration in response to stimulation by epinephrine in muscle or glucagon in liver.
2. Which compounds are responsible for the coordinated regulation of glucose and glycogen metabolism?
A. NADH
B. NAD+
C. Acetyl co-A
D. Fructose 2, 6-bisphosphate
Answer: D
Clarification: The hormonal regulation of glycolysis and gluconeogenesis is mediated by fructose 2, 6-bisphosphate.
3. Glycogen synthase a is activated by ___________
A. Phosphorylation catalyzed by GSK3
B. Dephosphorylation catalyzed by GSK3
C. Phosphorylation catalyzed by pyruvate kinase
D. Phosphorylation catalyzed by pyruvate carboxylase
Answer: A
Clarification: A protein kinase (PDK-1) that is activated when bound to PIP3 activates a second protein kinase (PKB. which phosphorylates glycogen synthase kinase 3 (GSK-3). The inactivation of GSK3 allows PP1 to dephosphorylate glycogen synthase converting it to its active form.
4. Glucagon is released from ___________
A. Muscle
B. Pancreas
C. Kidneys
D. Epithelial tissues
Answer: B
Clarification: Glucagon is released from pancreas and causes the liver to convert glycogen to glucose.
5. Glucose 6-phosphatase is present only in ___________
A. Liver
B. Muscle
C. Epithelial tissues
D. Kidneys
Answer: A
Clarification: Glucose 6-phosphatase which hydrolyzes glucose 6-phosphate is present only in liver. Other tissues lack glucose 6-phosphatase.
6. Which of the following enzymes is involved in the positive regulation of glycolysis/gluconeogenesis?
A. Hexokinase II
B. Hexokinase IV
C. PFK-2/FBPase-2
D. Pyruvate kinase
Answer: C
Clarification: Increased expression of PFK-2/FBPase-2 regulates glycolysis/gluconeogenesis.
7. Which of the following enzymes is involved in fatty acid synthesis?
A. Hexokinase II
B. Hexokinase IV
C. PFK-2/FBPase-2
D. Pyruvate dehydrogenase
Answer: D
Clarification: Hexokinase II and hexokinase IV involved in glycolysis.
8. Which of the following is involved in triacylglycerol synthesis?
A. Hexokinase II
B. Acyl co-A glycerol transferases
C. PFK-2/FBPase-2
D. Pyruvate dehydrogenase
Answer: B
Clarification: Hexokinase II involved in glycolysis, pyruvate dehydrogenase involved in fatty acid synthesis.
9. Which of the following is involved in pentose phosphate pathway?
A. Glucose 6-phosphate dehydrogenase
B. Acyl co-A glycerol transferases
C. PFK-2/FBPase-2
D. Pyruvate dehydrogenase
Answer: A
Clarification: Acyl co-A glycerol transferases involved in triacylglycerol synthesis, pyruvate dehydrogenase involved in fatty acid synthesis.
10. Which of the following enzyme’s gene expression is slowed by insulin?
A. Hexokinase II
B. Hexokinase IV
C. PEP carboxykinase
D. Pyruvate kinase
Answer: C
Clarification: Insulin stimulates the transcription of the genes that encode hexokinase II, hexokinase IV and pyruvate kinase.