Q: Which of the following equations correctly represents the conversion of glucose to glucose-6-phosphate during glycogenesis?

$$\mathrm{Glucose} + \mathrm{ATP} \rightarrow \mathrm{Glucose\text{-}6\text{-}phosphate} + \mathrm{ADP}$$

Question 1

Which of the following statements best explains why blood glucose is an absolute requirement for the brain?

Accepted Answer

Glucose is the greatly preferred energy source for the brain because it cannot utilize fatty acids due to the blood-brain barrier.

Question 2

Which enzyme is responsible for catalyzing the formation of the α(1→4) glycosidic bonds during glycogen synthesis?

Accepted Answer

Glycogen synthase

Question 3

A patient presents with muscle weakness and accumulation of glycogen in lysosomes. Which enzyme deficiency is most likely responsible for this presentation?

Accepted Answer

Acid maltase (lysosomal α(1→4)-glucosidase)

Question 4

Which of the following best describes the structure of glycogen?

Accepted Answer

A branched polymer of α-D-glucose with α(1→4) linkages and α(1→6) branches every 8–10 residues

Question 5

During glycogenolysis, which enzyme is responsible for removing the single glucose residue attached by an α(1→6) linkage at a branch point?

Accepted Answer

Amylo-α(1→6)-glucosidase (debranching enzyme)

Question 6

Which of the following is a direct consequence of the highly branched structure of glycogen?

Accepted Answer

Increased solubility and accelerated rates of synthesis and degradation

Question 7

What is the role of UDP-glucose in glycogen synthesis?

Accepted Answer

It is the activated form of glucose that donates glucosyl residues for chain elongation.

Question 8

Which process is primarily responsible for maintaining blood glucose levels during fasting?

Accepted Answer

Glycogenolysis in the liver

Question 9

A defect in the branching enzyme (amylo-α(1→6)-transglucosidase) would most likely result in which of the following?

Accepted Answer

Formation of abnormally long, unbranched glycogen chains

Question 10

Which of the following equations correctly represents the conversion of glucose to glucose-6-phosphate during glycogenesis?

Accepted Answer

$$\mathrm{Glucose} + \mathrm{ATP} ightarrow \mathrm{Glucose	ext{-}6	ext{-}phosphate} + \mathrm{ADP}$$

Question 11

Which regulatory mechanism is responsible for activating glycogen phosphorylase in muscle during intense exercise?

Accepted Answer

Phosphorylation by phosphorylase kinase activated by Ca$$^{2+}-$$calmodulin complex

Question 12

Which of the following best describes the fate of glucose-6-phosphate derived from muscle glycogen?

Accepted Answer

It enters glycolysis to provide ATP for muscle contraction.

Question 13

Which hormone promotes glycogen synthesis by activating protein phosphatase-1, leading to dephosphorylation of glycogen synthase?

Accepted Answer

Insulin

Question 14

Which of the following steps in glycogen metabolism requires a primer, and what is the protein involved?

Accepted Answer

Glycogenesis; glycogenin

Question 15

A patient with a deficiency in glucose-6-phosphatase would most likely present with which of the following symptoms?

Accepted Answer

Hypoglycemia due to inability to release free glucose from the liver

Question 16

Which of the following equations represents the formation of UDP-glucose from glucose-1-phosphate?

Accepted Answer

$$\mathrm{Glucose	ext{-}1	ext{-}phosphate} + \mathrm{UTP} ightarrow \mathrm{UDP	ext{-}glucose} + \mathrm{PP_i}$$

Question 17

Which of the following is a key difference between liver and muscle glycogen metabolism?

Accepted Answer

Liver glycogen can be converted to free glucose and released into the bloodstream, while muscle glycogen is used locally for energy.

Question 18

Which of the following best explains the effect of epinephrine on hepatic glycogen metabolism during a 'fight or flight' response?

Accepted Answer

Epinephrine stimulates glycogenolysis by activating phosphorylase kinase via a Ca$$^{2+}-$$calmodulin-dependent pathway.

Question 19

Which of the following is a multi-step process that occurs during the removal of glycogen branches?

Accepted Answer

Debranching enzyme first transfers three glucosyl residues to another chain (α(1→4)-glucan transferase activity), then hydrolyzes the α(1→6) bond to release free glucose (amylo-α(1→6)-glucosidase activity).

Glycogen Metabolism: Structure, Function, and Regulation

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