Glycogen Flashcards

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Questions and Answers

What is glycogen?

A polymer of glucose molecules used to store glucose.

Why is it important to store glucose? (Select all that apply)

The brain always needs glucose to function (correct)

Glucose can generate ATP without oxygen (correct)

Glycogen can be rapidly broken down in times of increased activity (correct)

None of the above

Where is glycogen stored? (Select all that apply)

Adipose tissue

Liver for body use (correct)

Bloodstream

Muscles for muscle use (correct)

How is glycogen stored?

In large granules in the cytosol of cells, granules contain highly branched polymers of glucose. Signup and view all the answers

Describe the structure of glycogen. (Select all that apply)

Each chain has 12-14 glucose linked via a(1-->4) Signup and view all the answers

Describe the polarity of glycogen.

There is a free anomeric carbon known as the reducing end and a free 4'OH known as the non-reducing end. Signup and view all the answers

Does making glycogen cost energy?

True Signup and view all the answers

Describe the process of synthesizing a glycogen chain (not the branch part).

Glucose-6-phosphate is converted to glucose-1-phosphate, which then forms UDP-glucose, and glycogen synthetase transfers glucose to the glycogen chain. Signup and view all the answers

What is the major regulatory enzyme of glycogen synthesis?

Glycogen synthase Signup and view all the answers

How are branched chains of glycogen formed?

A branching enzyme transfers a 7 glucose residue segment from the non-reducing end and forms an a(1-->6) linkage. Signup and view all the answers

What is the result of adding a branch to a glycogen chain?

Makes the molecule more water soluble and creates more reducing ends. Signup and view all the answers

Describe glycogen breakdown (not debranching).

Glycogen phosphorylase removes a glucose molecule from the non-reducing end by adding a Pi, yielding glucose-1-phosphate. Signup and view all the answers

Where does glycogen phosphorylase stop?

4 residues before a branch point. Signup and view all the answers

Does the phosphorylation of glucose in glycogen breakdown require ATP?

False Signup and view all the answers

Describe debranching.

A transferase shifts 3 residues from one branch to the other and the remaining a(1-->6) linked glucose is cleaved by a1,6-glucosidase. Signup and view all the answers

What are the fates of glucose-6-phosphate? (Select all that apply)

Glycolysis (muscles) Signup and view all the answers

Study Notes

Glycogen Overview

Glycogen is a polymer of glucose molecules, serving as a storage form of glucose in the body.
Essential for providing immediate energy, particularly for the brain and during physical activity.

Storage of Glycogen

Stored in muscles for muscle-specific use and in the liver for distribution throughout the body.
Stored in large granules within the cytosol of cells, featuring highly branched glucose polymers.

Structure of Glycogen

Contains chains consisting of 12-14 glucose units linked by α(1→4) glycosidic bonds.
Branch points occur at the 5th or 6th glucose unit, linking two chains through α(1→6) bonds.
Each chain typically possesses two branch points, giving glycogen a curved structure due to its linkages.

Polarity and Energy Cost

Characterized by a free anomeric carbon (reducing end) and a free 4'OH (non-reducing end).
Synthesizing glycogen requires energy, indicated by ATP expenditure.

Glycogen Synthesis Process

Glucose-6-phosphate is converted to glucose-1-phosphate by phosphoglucomutase.
UDP-glucose is formed from glucose-1-phosphate and UTP, releasing pyrophosphate.
Pyrophosphate is irreversibly hydrolyzed, ensuring the synthesis process's irreversibility.
Glycogen synthase transfers glucose from UDP-glucose to the non-reducing end of glycogen, elongating the chain.

Regulation and Branching

Major regulatory enzyme for glycogen synthesis is glycogen synthase.
Branching enzymes create branches by transferring a segment of 7 glucose residues from an outer chain to another chain, producing α(1→6) linkages.

Impact of Branching on Glycogen

Addition of branches enhances glycogen's water solubility and increases the number of reducing ends for metabolism.

Glycogen Breakdown Process

Glycogen phosphorylase catalyzes the phosphorolysis of glycogen, yielding glucose-1-phosphate and a shorter glycogen chain.
This process does not utilize ATP, as the phosphorylation of glucose occurs by adding inorganic phosphate (Pi).

Stopping Points and Debranching

Glycogen phosphorylase halts four residues before a branch point during breakdown.
Debranching involves a transferase shifting three residues from one branch to another and cleaving the remaining glucose through α1,6-glucosidase, yielding free glucose.

Fates of Glucose-6-Phosphate

Can enter glycolysis for energy production in muscles.
Cleaved by glucose-6-phosphatase in the liver to release free glucose into the bloodstream.
Can also enter the pentose phosphate pathway to generate ribose and NADPH for various cellular processes.

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Description

Test your knowledge on glycogen with these flashcards. Learn about its definition, storage, and importance for bodily functions, particularly during increased activity. A great resource for students studying biochemistry or human physiology.