Glycogen synthesis and regulation

Question 1

Summarise the differences between glycogen and glucose

Answer 1

Glycogen is the polymer of glucose

Glucose is the immediate energy source whilst glycogen is the medium fuel store

glucose- 10g in plasma
glycogen- 400g in tisssue stores

glucose is osmotically active whilst glycogen is not

Question 2

Role of glycogen in liver

Answer 2

The liver is sensitive to the blood glucose concentration so acts to maintain this with the control of insulin and glucagon.

When blood glucose concentration is lower than normal:
glycogen —> glucose-6-phosphate —-> glucose ( diffuses into capillaries)

Insulin triggers the synthesis and storage
Glucagon- triggers breakdown

Question 3

Role of glycogen in muscle

Answer 3

The muscle is sensitive to the demand of energy from the muscle tissue itself
ADRENALINE
CALCIUM
AMP- BECOMING DESPERATE FOR ENERGY- DEMAND INCREASES AND SUPPLY DECREASES
ATP

Glycogen —> glucose-6-phosphate —-> energy for contraction + lactate

Question 4

Describe a useful property of glycogen

Answer 4

Branched- meaning that there are several terminal residues - this increases the surface area for enzymes to function and so more glucose is released and quicker

Question 5

Features of biosynthetic pathways

Answer 5

ATP, GTP,UTP are all cofactors which drive the reactions forward

One or more of the enzymes reactions is irreversible
Alternative enzymes used in opposite direction

Enzymes at the start and the end of the reaction are highly regulated

Question 6

Summarise the formation of glycogen

Answer 6

Glycogen synthase extends in straight lines

Branching enzyme introduces the site for new chains for then glycogen synthase to continue.

Question 7

How does one activate glycogen syntase

Answer 7

DEPHOSPHORYLATE IT- covalent modification

using protein phosphatase dephosphorylate inactive form to the active form.

INSULIN

Question 8

How does one deactivate glycogen synthase

Answer 8

PHOSPHORYLATE IT- covalent modification

using protein kinase and ATP

GLUCAGON/ ADRENALINE

Question 9

Summarise the events of glycogen synthesis

Answer 9

glucose —> glucose-6-phosphate—> glucose-1-phosphate—-> ADP glucose—-> added to protein primer (using glycogen synthase)

Question 10

How does one release free glucose ?

Answer 10

1. Glycogen phosphorylase removes glucose one unit at a time ( debranching enzyme acts on 1,6 glysocidic bond)
2. This releases glucose-1-phosphatase
3. Phosphoglucomutase acts on glucose-1-phosphatase to form glucose-6-phosphatase Glucose-6-phosphotase from the liver forms glucose

Question 11

How does one activate glycogen phosphorylase

Answer 11

PHOSPHORYLATING IT-

using protein kinase and ATP

GLUCAGON/ADRENALINE

Question 12

How does one deactivate glycogen phosphorylase

Answer 12

DEPHOSPHORYLATING IT

using protein phosphatase

INSULIN

Question 13

Controls in the liver?

Answer 13

responds ot insulin/glucagon-

when blood glucose increases it binds to glycogen phosphorylase inactivating it

Question 14

Controls in the muscle?

Answer 14

during muscle contraction, Ca 2+ is released from the sarcoplasmic reticulum, which then binds to calmodulin domain of glycogen phosphorylase kinase activating it. This in turn activates phosphorylase- glycogen is degraded

During prolonged exercise- ATP —> AMP
ATP concentrations decrease and AMP is the allosteric activator of glycogen phosphorylase

Glycogen is degraded

Question 15

Glycogen storage diseases

Answer 15

Von Gierke’s- Glucose-6-phosphatase- enlarged liver, hypoglaecemia

Pompe’s-= lysosomal glycosides- muscle weakness, cardiac failure

McArdle’s -glycogen phosphorylase- excercise intolerance