9. Glycogen Metabolism

Question 1

How are residues and branches linked and what is the percentage of each?

Answer 1

Residues: a-1,4-glycosidic bonds: 93%
Branches: a-1,6-glycosidic bonds: 7%

Question 2

Main storage sites

Answer 2

Liver and muscle

Question 3

What is glucostat used for?

Answer 3

Maintain BG levels to balance out episodic nature of food intake

Question 4

Role of adrenaline in glycogenolysis

Answer 4

Fight or flight response induces glycogen breakdown, frequently too

Question 5

In glycogenesis, what is the ratio of ATP:Glucose?

Answer 5

2:1

Question 6

What is the active form of glucose?

Answer 6

UDP-Glucose

Question 7

What enzyme creates glycogen?

Answer 7

Glycogen synthase

Question 8

Which 3 enzymes are needed to synthesise glycogen?

Answer 8

UDP-Glucose Pyrophosphorylase
Glycogen Synthase
Branching Enzyme (amylo-1,4 -> 1,6-transglycosylase)

Question 9

What is glucosyl residue from UDP-glucose used for?

Answer 9

Transferred to non reducing end of glycogen to form an a-1,4-glycosidic bond

Question 10

Why is the primer glycogenin needed?

Answer 10

Glycogen synthase is only able to extend an existing chain

Question 11

Catabolic process that results in the formation of free glucose or G-6-P

Answer 11

Glycogenolysis

Question 12

What enzyme degrades glycogen?

Answer 12

Glycogen phosphorylase

Question 13

What is released when glycogen is degraded?

Answer 13

Glucose-1-phosphate

Question 14

At which end is glycogen degraded?

Answer 14

Non-reducing end

Question 15

How many G-1-P residues are released per branch point?

Answer 15

7-9

Question 16

Give two reasons why glycogen breakdown is rapid

Answer 16

Cascade mechanism

Multiple branch points

Question 17

3 enzymes needed for glycogenolysis

Answer 17

Glycogen phosphorylase
Transferase
Glycogen debranching enzyme

Question 18

What converts G-1-P to G-6-P?

Answer 18

Phosphoglucomutase

Question 19

What is the fate of G-6-P in the liver and muscles?

Answer 19

Liver has G-6-Phosphotase; release free glucose for export

Muscle; must use locally in glycolysis

Question 20

Can glycogenesis and glycogenolysis occur at the same time and why?

Answer 20

No

Hydrolysis of UTP-Glucose prevented by futile cycle

Question 21

How are glycogenesis and glycogenolysis controlled?

Answer 21

Allosteric regulation

Hormonal control (insulin, glucagon and adrenaline)

Covalent modification of phosphorylases and synthases

Question 22

Explain the effects of adrenaline and glucagon on glycogen regulation

Answer 22

Increase glycogen breakdown by stimualtion glycogen phosphorylase, also reducing glycogen synthase activity

Question 23

Explain the effects of insulin on glycogen regulation

Answer 23

Increases glycogen synthase activity

Reduces glycogen phosphorylase activity

Question 24

When is glucagon released and by which cell and in which organ?

Answer 24

a-cells of pancreas

Question 25

Which organ does glucagon act on?

Answer 25

Liver

Question 26

How is glucose released?

Answer 26

Into the bloodstream

Question 27

Explain how the glycogen cascade is stopped

Answer 27

Adrenaline level falls; dissociates from receptor
cAMP synthesis stops
Existing cAMP to 5’ cAMP by cAMP phosphodiesterase
Decline in cAMP shuts off activation cascade
Phosphorylated enzymes restored by dephosphorylation