Chapter 11

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Questions and Answers

What is the effect of elevated insulin levels on glycogen metabolism?

Decreased both glycogen synthesis and degradation

Increased glycogenolysis and decreased glycogenesis

Activation of glycogen phosphorylase

Increased glycogenesis and decreased glycogenolysis (correct)

What role does Ca2+ play during exercise in muscle glycogen metabolism?

It phosphorylates glycogen phosphorylase

It activates phosphorylase kinase (correct)

It activates protein phosphatase-1

It activates glycogen synthase directly

Which of the following statements is true regarding glycogen phosphorylase and glycogen synthase following stimulation by epinephrine?

Glycogen phosphorylase is phosphorylated and active, while glycogen synthase is phosphorylated and inactive (correct)

Glycogen phosphorylase is phosphorylated and inactive

Glycogen synthase remains unphosphorylated and active

Both are phosphorylated and active

Which enzyme deficiency results in exercise intolerance without elevation in blood lactate levels?

Myophosphorylase Signup and view all the answers

What is the primary consequence of glucose 6-phosphatase deficiency?

Inability to generate free glucose from glycogen and gluconeogenesis Signup and view all the answers

In the well-fed state, what is the effect of glucose 6-phosphate on glycogen metabolism?

Both activates glycogen synthase and inhibits glycogen phosphorylase Signup and view all the answers

What happens to glycogen metabolism when both epinephrine and glucagon are present?

They promote glycogenolysis and decrease glycogenesis Signup and view all the answers

What is characterized by generalized accumulation of glycogen and severe hypotonia?

Acid maltase deficiency Signup and view all the answers

The phosphorylation of glycogen synthase leads to which state of the enzyme?

Inactive Signup and view all the answers

What is the primary glycosidic bond in glycogen?

α(1→4) linkage Signup and view all the answers

Which enzyme is responsible for synthesizing UDP-glucose?

UDP-glucose pyrophosphorylase Signup and view all the answers

Which enzyme cleaves the α(1→4) bonds in glycogen to produce glucose 1-phosphate?

Glycogen phosphorylase Signup and view all the answers

What is produced after the cleavage of a limit dextrin?

Free glucose Signup and view all the answers

What happens to glucose 6-phosphate in the muscle cells?

It enters glycolysis Signup and view all the answers

Which condition results from a deficiency of glucose 6-phosphatase?

Glycogen storage disease Type 1a (Von Gierke disease) Signup and view all the answers

What role does glycogen serve in liver cells?

To maintain blood glucose concentration during fasting Signup and view all the answers

What type of linkage forms branches in glycogen?

α(1→6) linkage Signup and view all the answers

Which enzyme transfers glucosyl residues to another glycogen chain during the formation of branches?

Glucosyl 4:6 transferase Signup and view all the answers

What remains after the sequential degradation of glycogen by phosphorylase?

Limit dextrin structure Signup and view all the answers

Study Notes

Glycogen Overview

Major glycogen storage sites: skeletal muscle (fuel for ATP during contraction) and liver (regulation of blood glucose during fasting).
Glycogen structure: highly branched polymer of α-D-glucose with α(1→4) linkages and branches connected by α(1→6) linkages.

Glycogen Synthesis

Key building block: uridine diphosphate (UDP)-glucose, formed from glucose 1-phosphate and UTP via UDP-glucose pyrophosphorylase.
Glycogen synthase catalyzes the addition of glucose from UDP-glucose to glycogen chains by forming α(1→4) linkages.
Branching occurs through glucosyl 4:6 transferase, transferring groups of six to eight glucosyl residues.

Glycogen Degradation

Glycogen phosphorylase breaks α(1→4) bonds, generating glucose 1-phosphate.
Limit dextrin structure remains when four glucosyl units are left at branch points.
Debranching enzyme processes limit dextrin via glucosyl 4:4 transferase and amylo-(1→6) glucosidase, releasing free glucose.
Glucose 1-phosphate converts to glucose 6-phosphate by phosphoglucomutase; enters glycolysis in muscles or released as free glucose in liver.

Glycogen Storage Disease (GSD)

Type Ia (Von Gierke disease): glucose 6-phosphatase deficiency leads to severe fasting hypoglycemia and inability of liver to provide glucose.
Type VI: liver phosphorylase deficiency results in mild hypoglycemia and ability to produce glucose via gluconeogenesis.

Hormonal Regulation

Insulin increases glycogenesis (activates glycogen synthase) and decreases glycogenolysis.
Glucagon and epinephrine increase glycogenolysis (activate phosphorylase) and decrease glycogenesis via phosphorylation of enzymes.
cAMP-dependent protein kinases and protein phosphatase-1 play crucial regulatory roles.

Enzyme Regulation

Glycogen synthase is activated by glucose 6-phosphate in a fed state; inhibited by ATP.
Phosphorylase activity is increased by Ca2+ in muscle, activating phosphorylase kinase.
AMP also acts as an activator for glycogen phosphorylase in muscle.

Study Questions Summary

Myophosphorylase deficiency leads to exercise intolerance, preventing muscle glycogen degradation.
Branching enzyme deficiency results in glycogen with long outer chains and solubility issues.
Acid maltase deficiency affects multiple tissues, particularly heart, causing glycogen accumulation.
Glucose 6-phosphatase deficiency results in severe fasting hypoglycemia and metabolic abnormalities.
Glycogen metabolism in liver is affected by phosphorylation: phosphorylase active and synthase inactive when signals from epinephrine/glucagon are present.
Rapid calcium release in muscle activates phosphorylase kinase, enhancing glycogen breakdown.

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Description

This quiz explores the storage and function of glycogen in the body, particularly in skeletal muscle and the liver. Understand the structural components of glycogen, including its glycosidic bonds and role in energy synthesis. Test your knowledge on how glycogen maintains blood glucose levels during fasting.