Q: Which of the following equations correctly represents the reaction catalyzed by UDP-glucose pyrophosphorylase?

$Glucose\ 1\text{-}phosphate + UTP \rightarrow UDP\text{-}glucose + PP_i$

Question 1

Which of the following statements best describes the primary function of liver glycogen?

Accepted Answer

To maintain blood glucose concentration, especially during fasting

Question 2

What is the main glycosidic linkage found in the linear regions of glycogen?

Accepted Answer

α(1→4) linkage

Question 3

During glycogen synthesis, which enzyme catalyzes the formation of UDP-glucose from glucose 1-phosphate and UTP?

Accepted Answer

UDP-glucose pyrophosphorylase

Question 4

Which of the following is TRUE regarding the role of glycogenin in glycogen synthesis?

Accepted Answer

It serves as a primer by catalyzing the addition of the first few glucose residues from UDP-glucose.

Question 5

Which enzyme is responsible for cleaving α(1→4) glycosidic bonds during glycogenolysis?

Accepted Answer

Glycogen phosphorylase

Question 6

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

Accepted Answer

Acid α-glucosidase (acid maltase)

Question 7

Which of the following best explains why muscle glycogen cannot directly contribute to blood glucose levels?

Accepted Answer

Muscle cells lack glucose 6-phosphatase, so glucose 6-phosphate cannot be converted to free glucose.

Question 8

Which of the following reactions is catalyzed by phosphoglucomutase?

Accepted Answer

Conversion of glucose 6-phosphate to glucose 1-phosphate

Question 9

Which hormone stimulates glycogenolysis in the liver during periods of fasting?

Accepted Answer

Glucagon

Question 10

What is the effect of cAMP-dependent protein kinase A (PKA) activation on glycogen metabolism?

Accepted Answer

It inhibits glycogen synthase and activates glycogen phosphorylase.

Question 11

Which of the following best describes the branching enzyme's role in glycogen synthesis?

Accepted Answer

It transfers a block of 6–8 glucosyl residues from the nonreducing end to another residue, creating an α(1→6) linkage.

Question 12

Which of the following equations correctly represents the reaction catalyzed by UDP-glucose pyrophosphorylase?

Accepted Answer

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

Question 13

A deficiency in glucose 6-phosphatase leads to which glycogen storage disease and what is the primary metabolic consequence?

Accepted Answer

Von Gierke disease; inability to release free glucose during fasting

Question 14

Which of the following is a direct allosteric activator of muscle glycogen phosphorylase during intense exercise?

Accepted Answer

AMP

Question 15

Which process is accelerated in the well-fed state and inhibited during fasting?

Accepted Answer

Glycogenesis

Question 16

Which of the following best explains the increased solubility of glycogen compared to unbranched polysaccharides?

Accepted Answer

Glycogen is highly branched, increasing the number of nonreducing ends.

Question 17

Which of the following steps in glycogenolysis is unique to the liver and not found in muscle?

Accepted Answer

Conversion of glucose 6-phosphate to free glucose by glucose 6-phosphatase

Question 18

Which of the following best describes the reciprocal regulation of glycogenesis and glycogenolysis?

Accepted Answer

Glycogenesis is activated by insulin, while glycogenolysis is activated by glucagon and epinephrine.

Question 19

Which of the following is the correct sequence of events following epinephrine binding to its receptor in liver cells?

Accepted Answer

Activation of adenylate cyclase → increase in cAMP → activation of PKA → phosphorylation of phosphorylase kinase → activation of glycogen phosphorylase

Glycogen Metabolism: Structure, Synthesis, and Regulation

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