Glycogen Synthesis and Regulation

Question 1

Give 3 differences between glucose and glycogen.

Answer 1

Glucose is osmotically active, glycogen is not.
Glucose is a monosaccharide and glycogen is a polysaccharide.
Glucose is an immediate energy source, glycogen is a medium term fuel store.

Question 2

What is the role of glycogen in the liver?

Answer 2

Regulation of blood glucose levels (controlled by insulin and glucagon)

Question 3

What is the role of glycogen in muscles?

Answer 3

Sensitive to energy needs of tissue.

Releases energy for muscle contraction.

Question 4

Name the 2 types of linkage in glycogen

Answer 4

α-1,4-glycosidic linkages (straight)

α-1,6-glycosidic linkages (bent)

Question 5

What is the first stage of glycogen synthesis?

Answer 5

Conversion of glucose into glucose-1-phosphate.

Glucose > glucose-6-phosphate > glucose-1-phosphate

Question 6

What enzyme catalyses the conversion of glucose into glucose-6-phosphate?

Answer 6

Hexokinase

Question 7

What enzyme catalyses the reversible reaction of glucose-6-phosphate into glucose-1-phosphate?

Answer 7

Phosphoglucomutase

Question 8

Outline the 3 stages of glycogen synthesis.

Answer 8

1. Formation of glucose-1-phosphate from glucose.
2. Formation of UDP glucose
3. Addition of glucose unit to protein primer.

Question 9

Outline the formation of UDP-glucose from glucose-1-phosphate.

Answer 9

Glucose-1-phosphate + UTP > UDP-glucose

Uses an enzyme transferase.

Question 10

What enzyme is required in the formation of UDP-glucose?

Answer 10

Transferase (UDP-glucose-pyrophosphorylase)

Question 11

What is the importance of the protein primer glycogenin in glycogen synthesis?

Answer 11

Enables addition of glucose monomers to be added to its -OH group. Continuous addition onto the same strand forms a long glycogen strand.

Question 12

What enzyme catalyses the reaction of UDP-glucose with the protein primer to release UTP and add glucose onto the primer?

Answer 12

Glycogen synthase.

Question 13

What is the function of glycogen synthase?

Answer 13

To add glucose monomers onto the growing glycogen molecule. Forms glycogen.

Question 14

What is the function of protein phosphatase?

Answer 14

De-phosphorylates glycogen synthase to make it active.
Activates glycogen synthase.
Inactivates glycogen phosphorylase.

Question 15

What is the active form of glycogen synthase? Phosphorylated/unphosphorylated

Answer 15

Unphosphorylated

Question 16

What enzyme inactivates glycogen synthase?

Answer 16

Protein kinase

Question 17

What enzyme activate glycogen snthase?

Answer 17

Protein phosphatase

Question 18

What is the function of protein kinase?

Answer 18

Deactivates glycogen synthase by phosphorylating it.
Activates glycogen phosphorylase.
Initiates breakdown of glycogen.

Question 19

Outline the mechanism of glycogen breakdown (glycogenolysis).

Answer 19

Glyocgen phosphorylase adds phosphate group to remove a single glucose unit as glucose-1-phosphate.
Glucose-1-phosphate>glucose-6-phosphate>glucose

Question 20

What enzyme converts glucose-6-phosphate back into glucose?

Answer 20

Glucose-6-phosphatase

Question 21

What is the active form of glycogen phosphorylase?

Answer 21

Phosphorylated.

Question 22

What does glycogen phosphorylase do?

Answer 22

Initiates breakdown of glycogen.