Glycogen metabolism - regulation

Question 1

Glycogen phosphorylase is regulated by ________________ and ________________ _________________. GP is a homodimer with each subunit containing an active site and an allosteric site.

Answer 1

Allosterics

Covalent modification

Question 2

What are allosteric activators of glycogen phosphorylase?

Answer 2

AMP (muscle)

Question 3

What are the three allosteric inhibitors of glycogen phosphorylase?

Answer 3

1. ATP (muscle)
2. Glucose (liver)
3. Glucose-6-phosphate (muscle)

Question 4

Glycogen phosphorylase exists in two forms based on phosphorylation state. In what state is glycogen phosphorylase active?

Answer 4

Phosphorylated

Question 5

In what state is glycogen phosphorylase inactive?

Answer 5

Dephosphorylated

Question 6

Glycogen phosphorylase a refers to which of the two forms?

Answer 6

Active, phosphorylated

Question 7

Glycogen phosphorylase b refers to which form?

Answer 7

Inactive, dephosphorylated

Question 8

Glycogen phosphorylase is phosphorylated and activated by ________________ ______________ and dephosphorylated and deactivated by ______________ ___________________.

Answer 8

Glycogen phosphorylase kinase

Phosphoprotein phosphatase

Question 9

Glycogen phosphorylase kinase also exists in two forms, an a and a b form. Glycogen kinase a is the active form and __________________ while glycogen kinase b is the inactive form and _________________.

Answer 9

Phosphorylated

Dephosphorylated

Question 10

What phosphorylates and activates glycogen phosphorylase kinase?

Answer 10

Protein kinase A

Question 11

What dephosphorylates and deactivates glycogen phosphorylase kinase?

Answer 11

Protein phosphatase

Question 12

Glycogen phosphorylase acts as a ___________ ___________. Glucose binds to an allosteric site and exposes phosphates to action of phosphoprotein phosphatase.

Answer 12

Glucose sensor

Question 13

____________________ ___________________-1 is inactivated by inhibitor proteins that are also phosphorylated and activated in response to cAMP; therefore, glycogen phosphorylase is inhibited by cAMP.

Answer 13

Phosphaprotein phosphatase-1

Question 14

Glycogen synthase is regulated by allosterics and covalent modification. What is an allosteric activator of glycogen synthase?

Answer 14

Glucose-6-phosphate

Question 15

Glycogen synthase exists in two forms based on phosphorylation state. When is glycogen synthase inactivated?

Answer 15

When phosphorylated (GSb)

Question 16

Glycogen synthase is active in its a form when it is ____________________.

Answer 16

Dephosphorylated

Question 17

What dephosphorylates glycogen synthase and activates it?

Answer 17

Phosphoprotein phosphatase

Question 18

What phosphorylates and inactivates glycogen synthase?

Answer 18

Glycogen synthase kinase-3 (GSK-3)

Question 19

What is the role of phosphoprotein phosphatase-1?

Answer 19

Activated by insulin signal

Inactivated by PKA signal (indirect)

Question 20

What are the series of events that occur when glucagon binds to GPCR on hepatic cells? More specifically, what 5 things does PKA phosphorylate and the effects?

Answer 20

1. Activates glycogen phosphorylase
2. Activates FBPase2 of PFK2|FBPase2
   
   1. Decreases [F26BP]
      
      1. Activates FBPase1
      2. Deactivates PFK1
3. Activates PP1 inhibitor proteins
4. Deactivates glycogen synthase
5. Deactivates pyruvate kinase

Question 21

What is the net result of the glucagon signal in the liver?

Answer 21

Increased [glucose]_blood - active gluconeogenesis and glycogenolysis with glycolysis off

Question 22

_____________________ is a catecholamine hormone that signals fight or flight. It is produced in the adrenal glands and acts on adrenergic receptors as an agonist.

Answer 22

Epinephrine

Question 23

What is the ultimate result of the epinephrine signal on muscle cells?

Answer 23

Mobilization of fuel for energy production - active glycolysis and glycogenolysis

Question 24

Glucagon and epinephrine have similar effects in the liver and muscle. What are their differences?

Answer 24

Glucagon stimulates gluconeogenesis in the liver; epinephrine does not as muscle cells do not undergo gluconeogenesis

Question 25

How does the insulin signal serve to reverse the effects of the glucagon signal? In other words, what are the effec

Answer 25

1. Phosphoprotein phosphatase is active
   
   1. Inactivates glycogen phosphorylase kinase
   2. Inactivates glycogen phosphorylase
   3. Activates glycogen synthase
   4. Activates pyruvate kinase
   5. Activates phosphofructose kinase-2
      
      1. Increases [F26BP]
         
         1. Stimulates glycolysis