Regulation of Glycogenesis & Glycogenolysis (Exam 2)

Question 1

(TRUE/FALSE)

Glycogen synthase and glycogen phosphatase both catalyze irreversible reactions.

Answer 1

TRUE

Question 2

How is glycogen phosphatase regulated?

Answer 2

1. Allosterically
2. Covalent modulation

Question 3

What are the effectors of allosteric regulation in glycogen phosphatase?

Answer 3

1. ++ AMP (low energy levels)
2. – ATP (high energy levels)

Question 4

If glycogen phosphorylase is phosphorylated, is it active or inactive?

Which enzyme phosphorylates glycogen phosphorylase?

Answer 4

ACTIVE = PHOS (Glycogen phos A)

Phosphorylase kinase activates the enzyme, converts B to A

Question 5

If glycogen phosphorylase is dephosphorylated, is it active or inactive?

Which enzyme DEphosphorylates glycogen phosphorylase?

Answer 5

INACTIVE = DEPHOS (Glycogen phos B)

Phosphoprotein phosphatase inactivates this enzyme, converts A to B

Question 6

What is the key regulatory enzyme in glycogenesis?

Answer 6

Glycogen synthase

Question 7

What is the key regulatory enzyme in glycogenolysis?

Answer 7

Glycogen phosphorylase

Question 8

(TRUE/FALSE)

cAMP does inhibit glycolysis in muscle.

Answer 8

FALSE

It does NOT

Question 9

Explain the amplification mechanism and its effect on glycogenolysis.

Answer 9

The amplification mechanism is that one molecule of glucagon or epinephrine causes activation of cAMP signaling cascade which produces an enormous number of glucose-1-P molecules within a few seconds due to the increased surface area of glycogen due to branching.

Question 10

How is glycogen phosphatase allosterically regulated?

Answer 10

++ AMP (AMP is high during times of low energy levels within the cell)

– ATP (signals intracellular energy levels are high, so there is no need to start breaking down glycogen).

Question 11

Through what 2 enzymes is glycogen phosphorylase covalent modulated?

Answer 11

Phosphorylase kinase and phosphoprotein phosphatase

Question 12

When is glycogen phosphatase active?

Answer 12

ACTIVE = PHOSPHORYLATED (Glycogen phos A)

Phosphorylase kinase ACTIVATES the E, converts B to A

Question 13

When is glycogen phosphatase inactive?

Answer 13

INACTIVE = DEPHOS (Glycogen phos B)

Phosphoprotein phosphatase INACTIVATES the E, converts A to B

Question 14

How is glycogen synthase allosterically regulated?

Answer 14

++ Glucose-6-P
– CAMP

Question 15

In what state is glycogen synthase covalently activated?

Answer 15

ACTIVE = DEPHOS (Glycogen synthase A), this is catalyzed by ONE kinase (PHOSPHORYLASE KINASE) at ONE iste

Question 16

In what state is glycogen synthase covalently inactivated?

Answer 16

INACTIVE = PHOS (Glycogen synthase B), this is catalyzed by 11 different kinases, acting as second messengers (cAMP, Ca2+, etc).

Question 17

How is the covalent regulation of glycogen synthase different from glycogen phosphorylase?

Answer 17

The covalent regulation of glycogen synthase is much different, in that glycogen phosphorylase can only be phosphorylated by one specific protein (protein kinase), whereas glycogen synthase can be inactivated and shut down by at least 11 different kinase enzymes.

Question 18

How is glycogen synthase activated by insulin?

Answer 18

Insulin promotes the activation of glycogen synthase through activating phosphoprotein phosphatase activity by dephosphorylating glycogen synthase A; therefore, stimulating glycogenesis.