Chapter 9: 9.4 Glycogen Metabolism

Question 1

Glucose from ————- is transported across the —– ——- into —– and ——– —— —–

Answer 1

• Carbohydrates
• Lipid bilayer
• Liver
• Skeletal muscle cells

Question 2

What is glucose converted to when it is transported across the lipid bilayer?

Answer 2

Glucose-6-Phosphate (G6P)

Question 3

When the cell has used all the glucose it requires to meet it’s energy needs, it stores the rest of glucose as…

Answer 3

Glycogen

Question 4

Describe:

Glycolysis Synthesis

(2 points)

Answer 4

1. Glucose-6-Phosphate is converted to Glucose-1-Phosphate (G1P)
2. Glucose-1-Phosphate is added to the glycogen chain. This reaction is coupled with the hydrolysis of UTP –> UDP

Question 5

State:

The reaction where:
* Glucose-1-Phosphate is added to the glycogen chain

Answer 5

Glycogen (n residues) + G1P + UTP –> Glycogen (n+1 residues) + UDP + 2Pi

Question 6

What is the following reaction catalysed by?
* Glucose-1-Phosphate is added to the glycogen chain

Answer 6

Glycogen synthase

Question 7

True or False:

A separate enzyme is responsible for adding branch points to glycogen

Answer 7

True

Question 8

1. When does glycogen breakdown occur?
2. How does glycogen breakdown occur?

Answer 8

1. When the cell requires glucose
2. Glycogen phosphorylase removed G1P monomers from glycogen. Another enzyme moves phosphate group to make G1P&raquo_space; G6P

Question 9

True or False:

Glycogen breakdown is the reverse of glycogen synthesis

Answer 9

False

Question 10

Why is glycogen breakdown NOT the reverse of glycogen synthesis?

(2 points)

Answer 10

1. ΔG must be negative (energetically favourable) for both reactions
2. Having two different pathways also allows independent control of each pathway

Question 11

What are the methods of regulation of glycogen synthesis and breakdown?

Answer 11

1. Covalent modification of the enzymes in both pathways
2. Hormone signals dictate whether these enzymes are phosphorylated or unphosphorylated
3. Allosteric effectors

Question 12

In Regulation of Glycogen Synthesis and Breakdown:

What are the different covalent modifications of the enzymes in both pathways?

Answer 12

1. Phosphorylated glycogen synthase is LESS active than the dephosphorylated form
2. Phosphorylated glycogen phophorylase is MORE active than the dephosphorylated form

Question 13

In Regulation of Glycogen Synthesis and Breakdown:

In terms of hormone signals:
* What does insulin do?

Answer 13

Released by the pancreas when blood sugar levels are high
* Promotes glycogen synthesis
* Promotes dephopshorylation of glycogen synthase and glycogen phosphorylase

Question 14

In Regulation of Glycogen Synthesis and Breakdown:

In terms of hormone signals:
* What does glucagon do?

Answer 14

Acts when blood sugar is low
* Promotes glycogen breakdown (in liver only!)
* Promotes phosphorylation of glycogen synthase and glycogen phosphorylase

Question 15

What is released into the blood stream to maintain blood sugar levels?

Answer 15

Glucose

Question 16

In Regulation of Glycogen Synthesis and Breakdown:

In terms of hormone signals:
* What does epinephrine do?

Answer 16

Promotes phosphorylation of glycogen synthase and glycogen phosphorylase

Question 17

In Regulation of Glycogen Synthesis and Breakdown:

What are the allosteric effectors of skeletal muscles?

Answer 17

• Glycogen synthase: Activated by G6P
• Glycogen phosphorylase: Actaivated by AMP, inhibited by ATP

Question 18

In Regulation of Glycogen Synthesis and Breakdown:

What are the allosteric effectors of the liver?

Answer 18

• Glycogen phosphorylase: Inhibited by glucose

Question 19

True or False:

Allosteric effectors can override control by hormones and covalent modification

Answer 19

True