Glycogen Metabolism Lecture 22

Questions and Answers

What percentage of daily glucose consumption is utilized by the brain?

25%

50%

100%

75% (correct)

What is the primary reason for the liver's unique ability to release glucose into the bloodstream?

It is the primary site of glucose digestion.

It has a high concentration of glycogen.

It contains glucose 6-phosphatase. (correct)

It can convert fatty acids to glucose.

Why is glycogen preferred over triglycerides for short-term energy storage in the liver?

Glycogen is lighter than triglycerides.

Glycogen is more stable during fasting.

Glycogen can be converted to fatty acids readily.

Glycogen provides immediate energy without conversion. (correct)

What happens to excess glucose after a meal?

It is stored as glycogen in muscle and liver. Signup and view all the answers

What is the primary use of muscle glycogen during anaerobic conditions?

To generate glucose 6-phosphate for anaerobic glycolysis. Signup and view all the answers

What is the primary effect of glucagon on liver cells?

Stimulates glycogen degradation Signup and view all the answers

Which secondary messenger is involved in the signaling pathway activated by epinephrine?

cAMP (cyclic Adenosine Monophosphate) Signup and view all the answers

What is the role of Protein Kinase A in glycogen metabolism?

Phosphorylates glycogen phosphorylase Signup and view all the answers

How does Phosphorylase a contribute to glycogen degradation?

It cleaves glucose residues from the nonreducing ends Signup and view all the answers

What effect does Protein Kinase A have on glycogen synthase?

Phosphorylates it to reduce its activity Signup and view all the answers

Why does the body prefer to store excess glucose as glycogen instead of converting it all to triacylglycerols?

Glycogen can be rapidly mobilized for energy needs. Signup and view all the answers

What is the significance of the α-1,4 and α-1,6 glucose linkages in glycogen's structure?

They promote a highly branched structure for rapid energy release. Signup and view all the answers

How do insulin and glucagon differently affect glycogen metabolism?

Insulin stimulates glycogen synthesis while glucagon promotes degradation. Signup and view all the answers

What is necessary to activate glucose-1-phosphate for glycogen synthesis?

Conversion to UDP-glucose. Signup and view all the answers

In what way are liver cells unique concerning glucose-6-phosphate handling?

They can convert it back to free glucose for release into the bloodstream. Signup and view all the answers

What primary effect does elevated AMP levels have on glycogen metabolism in muscle cells?

It activates glycogen phosphorylase, leading to increased breakdown. Signup and view all the answers

Which disorder is associated with a deficiency of lysosomal glycogen degradation?

Glycogen storage disease. Signup and view all the answers

What is the main role of glycogen phosphorylase in glycogen metabolism?

It breaks down glycogen to glucose-1-phosphate. Signup and view all the answers

What is the role of epinephrine in glycogen degradation?

It stimulates the release of glucose into the bloodstream. Signup and view all the answers

What regulates glycogen breakdown in muscle besides cAMP?

Adenosine monophosphate (AMP) and calcium ions. Signup and view all the answers

What is a consequence of glycogen storage diseases affecting the liver?

Inability to produce glucose units for release into blood. Signup and view all the answers

How does phosphorylase kinase become activated in muscle?

Through Ca2+ binding to calmodulin. Signup and view all the answers

What is the primary purpose of glycogen breakdown during fasting?

To generate free glucose for bloodstream maintenance. Signup and view all the answers

What is the result of elevated AMP in muscle regarding phosphorylase b?

AMP activates phosphorylase b as an allosteric regulator. Signup and view all the answers

Which mechanism helps liver glycogenolysis to be stimulated by exercise?

Epinephrine binding to α-receptors. Signup and view all the answers

What dietary adjustment is recommended for individuals with liver-based glycogen storage diseases?

Maintaining proper blood glucose levels through diet. Signup and view all the answers

What potential symptom may result from glycogen storage diseases affecting skeletal muscle?

Increased risk of muscle cramps due to low energy. Signup and view all the answers

How do DAG and Ca2+ contribute to glycogen degradation?

They activate protein kinase C (PKC) for signaling pathways. Signup and view all the answers

What is the main structural feature of glycogen that allows for rapid degradation and synthesis?

Branched structure with multiple non-reducing ends Signup and view all the answers

In the liver, what is the unique function of glucose 6-phosphatase?

Convert glucose 6-phosphate to glucose Signup and view all the answers

Which enzyme is responsible for converting glucose to glucose 6-phosphate in tissues other than the liver?

Hexokinase Signup and view all the answers

What does glycogen phosphorylase require to function effectively?

Inorganic phosphate Signup and view all the answers

Which statement about the metabolism of fatty acids is true?

Acetyl CoA negatively modulates PDH. Signup and view all the answers

What role does UDP-glucose play in glycogen synthesis?

Provides energy for activating glucose monomers Signup and view all the answers

What happens to glycogen during hypoxia in tissues with low glycogen stores?

It is metabolized for energy. Signup and view all the answers

How does glucagon influence glycogen metabolism in the liver during fasting?

Activates glycogen phosphorylase Signup and view all the answers

Which enzyme has both transferase and α-1,6-glucosidase activity in glycogen degradation?

Debrancher enzyme Signup and view all the answers

What is the primary outcome of glycogenolysis in muscle tissue?

Production of glucose 6-phosphate for ATP generation Signup and view all the answers

Which enzyme is responsible for the phosphorylation of glucose to glucose 6-phosphate in the liver?

Glucokinase Signup and view all the answers

What is the effect of insulin on glycogen metabolism?

Activates glycogen synthase Signup and view all the answers

What happens to glycogen when lysosomal glucosidase is dysfunctional?

Glycogen accumulates in lysosomes Signup and view all the answers

Which of the following statements is true about the role of branching enzyme?

Creates α-1,6 branches in glycogen structure Signup and view all the answers

Study Notes

Glycogen Metabolism Overview

Glycogen serves as a primary storage form of glucose, enabling rapid energy mobilization.
The body stores excess glucose as glycogen instead of triglycerides because glycogen can be quickly mobilized to meet energy demands.

Glycogen Storage Locations

Muscle and liver tissues contain significant amounts of glycogen; muscle can store approximately 340g, and liver about 120g.
Other tissues maintain only small amounts of glycogen for emergency reserves.

Structure of Glycogen

Glycogen is a branched glucose polysaccharide linked by α-1,4 glycosidic bonds with α-1,6 branches approximately every 8-10 glucose residues.
The structure allows for compact storage and facilitates rapid synthesis and degradation due to multiple non-reducing ends for enzymatic action.

Glycogenolysis (Degradation)

Glycogen is broken down into glucose 1-phosphate (G1P) through glycogen phosphorylase in muscle, which is converted to glucose 6-phosphate (G6P) for ATP production.
In the liver, G6P is converted to free glucose for release into the bloodstream, maintaining blood glucose levels.

Glycogen Synthesis

Glycogen synthesis involves the conversion of glucose to glucose 6-phosphate (G6P) by hexokinase and to glucose 1-phosphate (G1P) by phosphoglucomutase.
UDP-glucose is formed from G1P, allowing the addition of glucose units to glycogen chains, catalyzed by glycogen synthase.

Hormonal Regulation

Insulin promotes glycogenesis by activating glycogen synthase and inhibiting glycogen phosphorylase, while glucagon (in fasting states) acts oppositely, promoting glycogenolysis.
Epinephrine triggers glycogen breakdown in response to low blood glucose and during exercise, enhancing the mobilization of glucose.

Amylopectin and Glycogen Structure

Glycogen's highly branched structure facilitates quick access for enzymes during both synthesis and degradation, ensuring efficient energy release.

Glycogen Storage Diseases

Disorders arise from deficiencies in enzymes responsible for glycogen synthesis or degradation, leading to hypoglycemia and muscle cramps.
Treatment often involves dietary management to maintain blood glucose levels or reducing physical exertion to prevent cramps.

Lysosomal Degradation

Lysosomal glucosidase breaks down glycogen into glucose; a deficiency leads to Pompe disease, affecting multiple organs, including the heart and muscles.

Immediate Result of Glycogen Degradation

The immediate degradation product of glycogen is glucose 1-phosphate, which is rapidly converted to glucose 6-phosphate for metabolic processes.

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Description

This quiz covers the key concepts of glycogen metabolism, including the rationale behind glycogen storage in the body instead of converting all excess glucose into triglycerides. Additionally, it explores the differences in glycogen storage between muscle and liver tissues. Test your understanding of these essential metabolic processes.