Final: glycogen metabolism

Question 1

where is glucose stored?

Answer 1

skeletal muscle and liver cells

Question 2

what is glucose stored as?

Answer 2

glycogen

Question 3

hormonal response to decrease in blood glucose levels + exercise

Answer 3

pancreas secretes glucagon

adrenal glands secrete epinephrine to increase heart rate

Question 4

glucagon

Answer 4

tells liver cells to break down glycogen

Question 5

epinephrine

Answer 5

increases heart rate

tells skeletal muscle cells to break down glycogen

Question 6

After eating a starchy meal,

Answer 6

1) increase in insulin acts on GLUTs (glucose transporters on cell membrane) which bring more glucose into our cells
2) Hexokinase adds phosphate to C6 of glucose (makes G6P)
3) G6P broken down to pyruvate during glycolysis (increases ATP)
4) ATP inhibits some glycolysis enzymes
- -> now we use G6P to make glycogen (liver + muscle)

Question 7

phosphorylated glycogen synthase is…

Answer 7

inactive

Question 8

phosphorylated glycogen phosphorylase is…

Answer 8

active

Question 9

why is glycogen breakdown different in liver and muscle?

Answer 9

liver has glycogen-6-phosphatase, muscle DOES NOT

Question 10

Glycogen breakdown in liver

Answer 10

HAS glucose-6-phosphatase

• removes phosphate from C6
• releases free glucose into bloodstream for other organs and tissues

Question 11

Glycogen breakdown in muscle

Answer 11

NO glucose-6-phosphatase

-uses G6P by sending it to glycolysis to make energy

Question 12

When is glycogen synthase active?

Answer 12

when it is not phosphorylated

Question 13

When is glycogen phosphorylase active?

Answer 13

when it is phosphorylated

Question 14

Regulation of glycogen metabolism depends on…

Answer 14

insulin and glucagon!

Question 15

regulation by insulin step 1

Answer 15

1) insulin attaches to tyrosine kinase receptor on cell surface

Question 16

regulation by insulin step 2

Answer 16

2) this activates a phosphatase which:
- removes phosphates from glycogen synthase (activates it)
- removes phosphates from glycogen phosphorylase (inactivates it)

increase in glycogen synthesis, decrease in glycogen degradation

Question 17

regulation by glucagon step 1

Answer 17

1) glucagon binds to GCPR on liver cell surface

Question 18

regulation by glucagon step 2

Answer 18

2) GCPR activates adenylyl cyclase (converts ATP to cAMP)

Question 19

regulation by glucagon step 3

Answer 19

3) cAMP activates protein kinase A

- protein kinase A adds phosphate to glycogen phosphorylase kinase (activates it)

Question 20

regulation by glucagon step 4

Answer 20

4) glycogen phosphorylase kinase adds phosphate to:
- glycogen phosphorylase (activates it)
- glycogen synthase (inactivates it)

increase in glycogen breakdown, decrease in glycogen synthesis