$$\mathrm{Glycogen}_{(n)} + \mathrm{Pi} \rightarrow \mathrm{Glycogen}_{(n-1)} + \mathrm{Glucose\text{-}1\text{-}phosphate}$$

Question 1

Which of the following best explains why animals store glucose as glycogen rather than as free glucose molecules?

Accepted Answer

Glycogen is osmotically inactive, preventing cellular swelling and damage.

Question 2

Which enzyme catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate during glycogenolysis?

Accepted Answer

Phosphoglucomutase

Question 3

During vigorous exercise, which allosteric effector most directly activates glycogen phosphorylase in skeletal muscle?

Accepted Answer

AMP

Question 4

Which of the following reactions represents the phosphorolytic cleavage of glycogen catalyzed by glycogen phosphorylase?

Accepted Answer

$$\mathrm{Glycogen}_{(n)} + \mathrm{Pi} ightarrow \mathrm{Glycogen}_{(n-1)} + \mathrm{Glucose	ext{-}1	ext{-}phosphate}$$

Question 5

Why is the formation of UDP-glucose from glucose-1-phosphate and UTP considered essentially irreversible under physiological conditions?

Accepted Answer

The reaction is coupled to the hydrolysis of pyrophosphate, which releases significant free energy.

Question 6

Which enzyme is responsible for introducing α(1→6) branch points during glycogen synthesis?

Accepted Answer

Branching enzyme (amylo-(1,4→1,6)-transglycosylase)

Question 7

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

Accepted Answer

Impaired release of free glucose from the liver during fasting

Question 8

Which of the following best describes the reciprocal regulation of glycogen synthase and glycogen phosphorylase by phosphorylation?

Accepted Answer

Phosphorylation activates glycogen phosphorylase and inactivates glycogen synthase.

Question 9

Which hormone is primarily responsible for stimulating glycogen breakdown in the liver during fasting?

Accepted Answer

Glucagon

Question 10

What is the physiological significance of glycogen's highly branched structure?

Accepted Answer

It increases the solubility and allows rapid mobilization and synthesis of glucose units.

Question 11

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

Accepted Answer

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

Question 12

Which of the following is a direct effect of epinephrine on skeletal muscle during the fight-or-flight response?

Accepted Answer

Activation of glycogen breakdown to provide glucose for ATP production

Question 13

Which of the following best describes the role of glycogenin in glycogen synthesis?

Accepted Answer

It serves as a primer by attaching the first glucose residue to itself.

Question 14

A mutation that prevents the dephosphorylation of glycogen synthase would most likely result in which metabolic consequence?

Accepted Answer

Impaired glycogen synthesis due to persistent enzyme inactivation

Question 15

Which of the following statements about the regulation of glycogen metabolism in the liver versus skeletal muscle is correct?

Accepted Answer

Liver glycogen phosphorylase is inhibited by glucose, while muscle glycogen phosphorylase is activated by AMP.

Question 16

Which of the following best explains the concept of signal amplification in hormonal regulation of glycogen metabolism?

Accepted Answer

A single hormone molecule can trigger a cascade, activating many enzyme molecules and resulting in a large metabolic response.

Question 17

Which of the following is a key energetic advantage of glycogenolysis over hydrolysis of glycogen?

Accepted Answer

Glycogenolysis releases glucose as glucose-1-phosphate, bypassing the need for ATP in the first step of glycolysis.

Question 18

Which enzyme is responsible for removing the α(1→6) branch point during glycogenolysis?

Accepted Answer

Debranching enzyme (α(1→6)-glucosidase activity)

Question 19

Which of the following best describes the effect of high ATP concentration on glycogen phosphorylase activity in skeletal muscle?

Accepted Answer

It inhibits glycogen phosphorylase, decreasing glycogen breakdown.

Glycogen Metabolism and Gluconeogenesis: Structure, Function, and Regulation

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