Glycogen

Question 1

Why is creation of glycogen necessary for glucose storage?

Answer 1

Glucose monomers alone are osmotically active (create difference in concentration across a membrane, which causes water to move across the membrane to make it equal).

Question 2

Glycogen is stored most in which tissues and why?

Answer 2

Muscles - to utilize for fast ATP synthesis.

Liver - for blood sugar maintenance (esp in times of fasting)

Question 3

When do muscles become dependent on glycogen?

Answer 3

During muscle contraction - blood cannot bring enough glucose to keep up and muscle cells are in an anaerobic environment so they can’t break down fatty acids.

Question 4

Which enzymes are responsible for glycogenolysis and what do they do?

Answer 4

Glycogen phosphorylase: releases the a-1,4 linked glucose residues from glycogen one at a time using inorganic phosphate. The product is glucose-1-phosphate.

Debranching enzyme: Breaks down the branches of glycogen to help degrade it into glucose. Product is glycogen straight chains

Question 5

Glycogen phosphorylase - what is it, and what is it responsive to?

Answer 5

key regulated enzyme in glycogen breakdown in muscle. Responsive to cell energy level, contractile state, and epinephrine (which stimulates it via making cAMP).

Question 6

Why is glycogen branched?

Answer 6

Many reducing ends = many places for degradation to start = fast degradation/utilization

Question 7

When do you want glycogen synthase to be active?

Answer 7

After a meal when there is a lot of glucose in the blood stream.

Question 8

What activates glycogen synthase?

Answer 8

Insulin, via dephosphorylation.

Question 9

What inactivates glycogen synthase?

Answer 9

Glucagon, via phosphorylation.