Glycogen Regulation

Question 1

A fasting man needs to break down glycogen; cAMP levels rise in liver cells to signal this. How does cAMP act to induce more glycogenolysis?

Answer 1

cAMP induces protein kinase A, which induces glycogen phosphorylase kinase, which induces glycogen phosphorylase to promote glycogenolysis

Question 2

Calcium and the calcium-calmodulin complex both stimulate the conversion of glycogen to glucose. Biochemically, how does this occur?

Answer 2

Both induce glycogen phosphorylase kinase, which in turn activates glycogen phosphorylase to break down more glycogen into glucose

Question 3

Via what 2 pathways does an activated insulin receptor trigger glycogenesis?

Answer 3

Direct glycogen synthase stimulation and indirect stimulation via protein phosphatase activation

Question 4

Glycogen is made from glucose by what enzyme?

Answer 4

Glycogen synthase

Question 5

Glucose is made from glycogen by what enzyme?

Answer 5

Glycogen phosphorylase via phosphorylation by glycogen phosph activation from PKA

Question 6

Glucagon stimulates the breakdown of glycogen. In what organ/tissue does it exert its effects? How?

Answer 6

Liver

It acts via a cAMP 2nd-messenger system (creates cAMP from ATP via adenylate cyclase)

Question 7

What 2 factors in muscle, by activating glycogen phosphorylase kinase, ensure that glycogenolysis is coordinated w/muscle activity?

Answer 7

Calcium and calmodulin

Question 8

Epinephrine can encourage glycogen breakdown by way of 2 pathways. What are they?

Answer 8

Via α-receptors (which stimulate ER release of calcium) or β-receptors (which act via the cAMP 2nd-messenger system)

Question 9

A pt under stress releases epinephrine, which binds to α-receptors. How does this help muscles contract more effectively?

Answer 9

Calcium exits the ER, inducing glycogen phosphorylase kinase (for glucose) and calcium-calmodulin (helps w/contractions)

Question 10

Name the 3 activators of the enzyme glycogen phosphorylase kinase.

Answer 10

Calcium from epinephrine activation of alpha receptos in the liver, calcium-calmodulin complex via beta receptors that activate adenylate cyclase to increase cAMP and activate pKA, and protein kinase A via glucagon receptor in liver

Question 11

What receptor does insulin bind to in liver and muscle cells? Which 2 enzymes does insulin directly stimulate to promote glycogen synthesis?

Answer 11

Tyrosine kinase dimer receptor

Insulin directly stimulates glycogen synthase and protein phosphatase

Question 12

A man receives an α-blocker and epinephrine. Glycogen breakdown ↑ significantly, but muscle contractility only ↑ mildly. Why?

Answer 12

α-Receptor binding (blocked) promotes both muscle contraction and glycogenolysis; β-receptor binding (open) promotes glycogenolysis