Met 1: Glycogen Metabolism

Question 1

Why is the branched structure of glycogen important?

Answer 1

Branching allows glucose monomers to be added/removed at multiple points. This makes glycogen synthesis and breakdown much FASTER

Question 2

3 Steps of glycogen synthesis (start with G6P)

Answer 2

1. G6P becomes G1P
2. G1P becomes UDP glucose (requires UTP)
3. UDP glucose added to glycogen chain (by glycogen synthase)

Question 3

Can glycogen synthesis begin with 1 glucose? 2 glucoses?

Answer 3

Trick question: glycogen synthesis can only begin if a small protein anchor is present (glycogenin)

Question 4

Compare the function of glycogen breakdown in muscle and liver

Answer 4

Muscle: glycogen breakdown provides energy (in the form of glucose) specifically for those cells

Liver: glycogen breakdown creates glucose monomers that go into blood stream (b/c liver has G6Phosphatase needed to get glucose out of the hepatocyte)

Question 5

What is the effect of G6P, ATP, and Glucose on glycogen?

Answer 5

G6P, ATP, Glucose all signal that the cell has plenty of energy and plenty of glucose —> promotes glycogen synthesis

Question 6

What is the effect of Calcium and AMP on glycogen?

Where are these regulators important?

Answer 6

• These regulators are important in MUSCLE
• Calcium and AMP both signal muscle activity, so promote breakdown of glycogen

Question 7

What is the key enzyme in glycogen synthesis?

Glycogenolysis?

Answer 7

• Glycogen synthesis: glycogen synthase
• Glycogenolysis (breakdown): glycogen phosphorylase

Question 8

In what part of the cell does glycogen metabolism occur?

In what tissues?

Answer 8

• Occurs in cytosol
• Liver and muscle

Question 9

Describe the effect of insulin on glycogen metabolism enzymes.

Answer 9

• Insulin promotes nutrient storage (glycogen synthesis) and dephosphorylates enzymes
• So, dephosphorylation must ACTIVATE glycogen synthase
• Dephosphorylation must INHIBIT glycogen phosphorylase

Question 10

Describe the effect of glucagon on glycogen metabolism

Answer 10

• Glucagon promotes release of glucose into the blood and phosphorylates enzymes
• So, phosphorylation must ACTIVATE glycogen phosphorylase
• Phosphorylation must INHIBIT glycogen synthase