Glycogen Metabolism Learning Objectives

What are the sources of chemical energy that power muscles on a timescale of seconds?

• ATP (stored): Very limited and lasts < 1 second

• Creatine Phosphate: Regenerates ATP from ADP → powers short bursts

What are the sources of chemical energy that power muscles on a timescale of minutes (anaerobic)?

• Uses muscle glycogen

• Produces ATP quickly

What are the sources of chemical energy that power muscles on a timescale of hours?

Oxidative metabolism: uses blood glucose and fatty acids

→ High ATP yield but slower

Why is glycogen an efficient storage form of glucose?

• Highly branched = many nonreducing ends

→ Allows rapid glucose release

• Compact storage

→ Stores large amounts without osmotic stress

• Energy efficient

→ Only 2 ATP to store glucose and 30 gained when oxidized

What is a “reducing sugar”?

A reducing sugar can open into a linear form, exposing an aldehyde or ketone that act as reducing agents (donate electrons)

What are the key distinctions between a reducing and non-reducing sugar?

Reducing-sugar: Free anomeric carbon that can open

Non-reducing sugar: anomeric carbon locked in glycosidic bond

How many reducing ends are in glycogen?

One reducing end

What is an anomeric carbon?

A carbon that forms a hemiacetals/acetal, determining an alpha or beta configuration

What are the anomeric carbons in an aldose v.s a ketone?

Aldoses (ex: Glc): C1

Ketoses (ex: Fructose): C2

Describe the structure of glycogen:

It is a polymer of glucose, that contain alpha(1→4) linear chains and alpha(1→6) bonds every 8-12 residues

→ Contains glycogen in protein core

→ NO beta bonds

Describe the outer branches of glycogen:

Outer branches contain nonreducing ends (metabolically active)

What are the 2 primary functions of glycogenin?

1. Primer formation: starts glycogen synthesis

2. Autoglycosylation: attaches first glucose residues to itself

→ It is required because glycogen synthase cannot start from scratch

What the 4 primary steps of glycogenolysis (glycogen breakdown)?

What are the substrates and products of glycogen phosphorylase?

What is the function of glycogen phosphorylase?

What is the function of phosphoglucomutase?

What is the function of Glucose-6-Phosphatase?

What reactants are required for the debranching process of glycogen?

Describe the regulation of Glycogen Phosphorylase by phosphorylation:

Describe the regulation of Glycogen Phosphorylase by AMP binding:

Describe the regulation of Glycogen Phosphorylase by glucose-6-phosphate binding:

What are the 3 regulatory mechanisms of glycogen phosphorylase?