Glycogen and Pentose Phosphate Pathway

Question 1

Muscle can burn either _________.

Answer 1

glucose or fat

Question 2

Glucagon and epinephrine lead to an increase in intracellular ______ that activates ________. That enzyme, when activated, phosphorylates ________.

Answer 2

cAMP; PKA; glycogen phosphorylase kinase (activating it)

Question 3

Glycogen phosphorylase kinase and glycogen phosphorylase are both activated by ___________. They work to break down glycogen.

Answer 3

being phosphorylated (which occurs in response to epinephrine, cortisol, glucagon, and growth hormone)

Question 4

____________ synthesis is inhibited by phosphorylation.

Answer 4

Glycogen

Question 5

Muscle glycogen stores can be exhausted in _________ of vigorous activity.

Answer 5

less than an hour

Question 6

Which enzyme converts glucose 6-phosphate to glucose 1-phosphate in the glycogen synthesis pathway?

Answer 6

Phosphoglucomutase

Question 7

Glycogen synthase adds glucose to the ______ end of glucose.

Answer 7

4’

Question 8

How can defects in glycogen synthesis simultaneously cause hepatomegaly and hypoglycemia?

Answer 8

If cells lack proper branching enzymes (utilized in glycogen synthesis), then they will have larger than normal stores of glycogen but be unable to use them quickly.

Question 9

Glycogen phosphorylase converts glycogen to _________.

Answer 9

glucose 1-phosphate

Question 10

The key stimulator of glycogen synthase and inhibitor of glycogen phosphorylase in the liver is __________.

Answer 10

glucose 6-phosphate

Question 11

How does intracellular calcium lead to glycogen breakdown?

Answer 11

Calcium binds to calmodulin which then activates glycogen phosphorylase kinase which phosphorylates glycogen phosphorylase (thus activating it); alternatively, PKA can also phosphorylate glycogen phosphorylase kinase.

AMP also allosterically activates glycogen phosphorylase.

Question 12

How is active phosphorylase kinase turned off?

Answer 12

Protein phosphatase (stimulated by insulin)

Question 13

PKA phosphorylates and thus _________ glycogen synthase.

Answer 13

deactivates

Question 14

The first enzyme in the pentose monophosphate pathway is _______________.

Answer 14

glucose 6-phosphate dehydrogenase

Question 15

Describe the differences between oxidative and non-oxidative phases in the pentose monophosphate pathway.

Answer 15

The oxidative pathway converts G6P to NADPH, while the non-oxidative pathway does the opposite (when glucose is low).