Metabolism V: Glycogen

Question 1

Glycogen degradation requires…

Answer 1

• glycogen phosphorylase
• debranching enzyme
• additional enzymes (kinases) that activate glycogen phosphorylase

Question 2

What are some of the second messenger systems involved with glycogen metabolism? Do they involve glycogen synthesis or degradation?

Answer 2

-cAMP
-PIP2: IP3 and DAG
-Ca2+
All of the above messengers play a role in glycogen degradation.

Question 3

Which type of linkage does glycogen phosphorylase help degrade?

Answer 3

It removes glycosyl units from an alpha-1,4 linkage, whereas debranching enzyme removes glycosyl units from an alpha-1,6 linkage.

Question 4

Is glycogen phosphorylase active or inactive when phosphorylated? What about glycogen synthase?

Answer 4

glycogen phosphorylase is active when phosphorylated; glycogen synthase is inactive when phosphorylated

Question 5

How does cAMP affect the muscle and liver in a similar vs. different way?

Answer 5

• similar: promotes glycogen degradation and inhibits glycogen synthesis
• different: inhibits glycolysis in the liver but activates glycolysis in muscle (cardiac and skeletal)

Question 6

Which enzyme helps activate glycogen phosphorylase? How?

Answer 6

Phosphorylase kinase activates glycogen phosphorylase by phosphorylating it.