Glycogen Metabolism

Question 1

Glycogen

Answer 1

Storage form of glucose in animals

Mostly in liver and muscle cells

Question 2

Step 1 of glycogen synthesis

Answer 2

Glucose 6-phosphate -> glucose 1-phosphate

Enzyme: phosphoglucomutase

Question 3

Step 2 of glycogen synthesis

Answer 3

Glucose 1-phosphate -> UDP-glucose

Enzyme: UDP-glucose pyrophosphorylase

Question 4

Step 3 of glycogen synthesis

Answer 4

Addition of UDP-glucose to the growing glycogen polymer

Enzyme: glycogen synthase

Question 5

Glycogen degradation

Answer 5

Glycogen phosphorylase catalyzes the removal of glucose residues from the non-reducing ends of glycogen (phosphorolysis reaction: transfer of glucose residue to phosphate)

Question 6

Limit dextrin

Answer 6

4-residue branched fork of glycogen formed from degradation of one end
4-alpha-glucanotransferase translocates 3 residues to another end
Amylo-1,6-glucosidase can remove lone branched glucose

Question 7

Insulin

Answer 7

Secreted from beta-cells in the pancreas when blood glucose levels increase
Stimulates glycogen synthesis

Question 8

Glucagon

Answer 8

Secreted from alpha-cells in the pancreas when blood glucose levels decrease
Stimulates glycogen degradation

Question 9

Epinephrine

Answer 9

Secreted by adrenal gland as part of the “fight or flight” response
Promotes glycogen degradation
Shorter term effect than insulin and glucagon

Question 10

How glycogen synthesis and degradation are regulated

Answer 10

Reciprocally regulated (1 is activated, other is deactivated)
Phosphorylation of enzymes by protein kinases and protein phosphatases

Question 11

Glycogen regulation by glucose

Answer 11

Glucose stimulates glycogen synthesis