Glycogenesis and Glycogenolysis

Question 1

Glycogen breakdown in muscle

Answer 1

Will only breakdown to make ATP, for its own benefit

Question 2

Glycogen breakdown in liver

Answer 2

Via glut2, the glucose will be sent to other tissues through the blood

Question 3

Amount of glycogen in muscle and liver

Answer 3

400 g muscle

100 g liver

Question 4

Insulin independent tissues

Answer 4

Must tissues (adipose, muscle...)
Use glut4

Question 5

Insulin dependent tissues

Answer 5

Erythro/leukocytes, lens, cornea, liver (uses glut2), brain

Question 6

Insulin stimulated translocation of glut4 to membrane

Answer 6

1. Insulin binds to tyrosine kinase (PKB)
2. Activated receptor promotes glucose transporters to membrane
3. Glucose transporters allow glucose uptake into cell

Question 7

Amp stimulated protein kinase translocation of glut4

Answer 7

In low insulin levels, muscles need glucose for energy. So high AMP and low ATP (from adenylate kinase reaction) will stimulate AMPK which will promote the translocation of glut4 transporters to the membrane during muscle contraction.

Question 8

Hexokinase

Answer 8

Km=.2mM
Constitutive enzyme (always have optimum levels)
In all tissues
Inhibited by product

Question 9

Glucokinase

Answer 9

Km=10mM
Induced enzyme (only optimum levels with inducer insulin)
In liver
Not inhibited by product

Increase glucose = increase activity

Question 10

Where is GK when you’re fasting?

Answer 10

Bound to GKRP (in hepatocyte nucleus)

Question 11

How does GK release from GKRP to cytosol?

Answer 11

High glucose and high F1P

Low F6P

Question 12

Glycogenesis overview

Answer 12

1. Glucose to G6P using hexokinase or GK (ATP hydrolysis)
2. G6P to G1P
3. G1P and UTP react making UDPGlucose and PPi
4. UDPGlucose is added to NR end of glycogen primer via glycogen synthase, liberated UDP
5. UDP and ATP will regenerate UTP

Question 13

Without a pre existing glycogen fragment, how is glycogen made?

Answer 13

Glycogenin will serve as a receptor of glucose residues. It is a protein dimer with RTKs are arranged head to toe.

Question 14

Glycogen synthetase

Answer 14

Forms alpha 1-4 bonds

Question 15

Branching enzyme

Answer 15

Glucosyl-4:6 transferase attaches alpha 1-6 bonds

Question 16

Glycogenolysis overview

Answer 16

Glycogen phosphorylase will phosphorylate a glucose at the NR end and will cause glycogen breakdown

Question 17

Glycogen phosphorylase specificity

Answer 17

Will cleave glycogen up to glucose molecule away from a branch, so a debranching enzyme will do the rest: a transferase will transfer the last 3 of the branch to the existing glycogen chain, and an alpha16 glucosidase will cleave off the branched glucose

Question 18

Regular levels of blood glucose

Answer 18

70 - 100 mg/dL

Question 19

When glycogen phosphorylase and glycogen synthase are phosphorylated, what happens?

Answer 19

Phosphorylated glycogen phosphorylase = active = glycogen breakdown
Phosphorylated glycogen synthase = inactive = no glycogen synthesis

Question 20

Active protein kinase a =

Answer 20

Phosphorylated phosphorylase kinase which will phosphorylate glycogen phosphorylase (= glycogenolysis), glycogen synthase (= no glycogenesis), and inhibitor 1 (= inhibit inhibitor (phosphoprotein phosphotase) = glycogenolysis).

Question 21

Glycogen synthase kinase 3

Answer 21

Phosphorylates glycogen synthase making it inactive

Question 22

What happens when epinephrine binds to alpha antagonist receptor?

Answer 22

Epi binds, activating specific G proteins to activate PLC. PLC turns PIP2 into IP3 and DAG. IP3 will then release Ca2+ from the ER. Calmodulin is then formed and PKC is also activated. Calmodulin will phosphorylate phosphorylase kinase and will phosphorylate glycogen phosphorylase and synthase. The calmodulin dependent protein kinase and PKC will also phosphorylate glycogen synthase.

Question 23

Regarding glycogen metabolism, insulin will

Answer 23

Limit cAMP production
Activate hepatic protein phosphotases
Activate phosphodiesterase that converts cAMP to AMP
Inactivate glycogen synthase kinase 3

Question 24

A high insulin/glucagon ratio means

Answer 24

More insulin, less glucagon, favoring glycogen synthesis

Question 25

Difference between glycogen metabolism regulation in muscle and liver

Answer 25

1. Glucagon has no effect on muscle
2. AMP and Ca2+ are activators of glycogen phosphorylase in muscle, not liver
3. Glucose is not an inhibitor of muscle glycogen phosphorylase

Question 26

Von gierkes disease

Answer 26

G6p problem
Severe hypoglycemia, ketosis, hyperuricemia, hyperlipemia
Liver and kidney

Question 27

Coris disease

Answer 27

Debranching enzyme problem
Like type 1 but milder
Muscle and liver

Question 28

Andersons disease

Answer 28

Branching enzyme
Liver failure
Liver

Question 29

Mcardles disease

Answer 29

Phosphorylase problem
Can’t preform strenuous exercise, normal life
Muscle

Question 30

Hers disease

Answer 30

Phosphorylase problem
Like type 1 but milder
Liver

Question 31

3 ways muscle glycogen can be phosphorylated

Answer 31

High amp after muscle contraction using ATP
Nerve impulses that release Ca2+
Epinephrine cascade resulting in high camp