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

$$\text{R}_2\text{C}_2 + 4\text{cAMP} \rightarrow 2\text{C} + \text{R}_2(\text{cAMP})_4$$

Question 1

Which of the following best describes the reaction catalyzed by glycogen phosphorylase?

Accepted Answer

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

Question 2

Which molecule acts as a positive allosteric effector of glycogen phosphorylase, increasing its activity during muscle contraction?

Accepted Answer

AMP

Question 3

Phosphorylation of Ser-14 on glycogen phosphorylase leads to which of the following effects?

Accepted Answer

A dramatic conformational change that activates the enzyme

Question 4

Which enzyme is responsible for removing phosphate groups from phosphorylated proteins, thus reversing the effects of kinases?

Accepted Answer

Phosphoprotein phosphatase-1

Question 5

Insulin promotes the storage of glucose by activating which process in the liver and muscle?

Accepted Answer

Glycogen synthesis

Question 6

Which hormone stimulates glycogen breakdown in the liver by activating glycogen phosphorylase?

Accepted Answer

Glucagon

Question 7

What is the role of cAMP in the signal transduction pathway of glucagon?

Accepted Answer

It acts as a second messenger to activate protein kinase A (PKA)

Question 8

Which of the following equations represents the activation of cAMP-dependent protein kinase (PKA)?

Accepted Answer

$$	ext{R}_2	ext{C}_2 + 4	ext{cAMP} ightarrow 2	ext{C} + 	ext{R}_2(	ext{cAMP})_4$$

Question 9

Which of the following is a direct effect of epinephrine binding to its receptor on muscle cells?

Accepted Answer

Activation of glycogen phosphorylase and increased glycogenolysis

Question 10

Which statement best explains the effect of ATP on glycogen phosphorylase activity?

Accepted Answer

ATP acts as a negative allosteric effector, decreasing enzyme activity

Question 11

Which of the following best describes the mechanism by which insulin signaling leads to increased glycogen synthesis?

Accepted Answer

Insulin activates protein phosphatases that dephosphorylate and activate glycogen synthase

Question 12

Which of the following is a key regulatory step in glycolysis that is hormonally controlled by both insulin and glucagon?

Accepted Answer

Phosphofructokinase-2 / Fructose-2,6-bisphosphatase

Question 13

Which of the following statements about the T and R states of allosteric enzymes is correct?

Accepted Answer

The R state has higher affinity for substrate than the T state

Question 14

Which of the following is the major site of action for glucagon?

Accepted Answer

Liver

Question 15

Which of the following is NOT a principle of hormone signal transduction described in the study materials?

Accepted Answer

Hormones always act by directly phosphorylating their target enzymes

Question 16

Which enzyme is activated by cAMP-dependent protein kinase (PKA) and is responsible for phosphorylating Ser-14 of glycogen phosphorylase?

Accepted Answer

Phosphorylase kinase

Question 17

Which of the following best explains the effect of calcium ions ($$	ext{Ca}^{2+}) on $$glycogen metabolism in muscle cells?

Accepted Answer

$$	ext{Ca}^{2+}$$ binds to calmodulin, activating phosphorylase kinase and promoting glycogen breakdown

Question 18

A patient with a deficiency in phosphoprotein phosphatase-1 would most likely exhibit which of the following metabolic abnormalities?

Accepted Answer

Impaired dephosphorylation of glycogen phosphorylase, leading to excessive glycogen breakdown

Question 19

Which of the following best describes the effect of epinephrine on liver metabolism during the 'fight or flight' response?

Accepted Answer

Epinephrine stimulates glycogenolysis and release of glucose into the blood

Regulation of Glycogen Metabolism: Enzymes, Hormones, and Signal Transduction

Study Guide - Practice Questions