Brenda - Glycogenolysis

Question 1

What happens in the early stages of fasting?
(5)

Answer 1

Liver glycogen stores are broken down

The liver plays a great role in maintaining blood glucose levels in the first 24 hours

After glycogen stores are depleted the body uses energy stores from adipose tissue

Fatty acids are the major source of energy after 24 hours

Ketone bodies are produced from fatty acids when liver glycogen is entirely depleted

Question 2

What happens in the body after an extended period of fasting?
(2)

Answer 2

The body begins breaking down proteins into amino acids and releasing them into the bloodstream

This allows for production of more glucose by gluconeogenesis

Question 3

Write a note on starch
(3)

Answer 3

Two forms: unbranched glucose polymer ‘amylose’ and branched polymer ‘amylopectin’

In both forms glucose residues are linked by alpha (1-4) glycosidic bonds

Amylopectin also has alpha (1->6) glycosidic bonds (branch points)

Question 4

Write a note on glycogen
(3)

Answer 4

A branched polymer of glucose residues

Contains same types of bonds as amylopectin a(1->6) but branches are smaller and more frequent

It accounts for up to 10% of mass of the liver, 2% mass of muscle in mammals

Question 5

What is the function of glycogen in the liver?
(3)

Answer 5

Glycogen synthesis

Glycogen breakdown

Both are regulated to maintain blood glucose levels

Question 6

What is the function of glycogen in the muscle?

Answer 6

Regulation of synthesis and breakdown of glycogen to meet the energy requirements of the muscle cell

Question 7

What is glycogenolysis?

Answer 7

The degradation of stored glycogen

Question 8

What enzyme degrades glycogen?

Answer 8

Glycogen phosphorylase

Question 9

How does glycogen phosphorylase degrade glycogen?

Answer 9

By cleaving sequential phospholytic cleavage of a(1->4) bonds

Question 10

What product is formed from the degradation of glycogen?

Answer 10

Glucose1Phosphate

Question 11

What is G1P converted into ?

Answer 11

Glucose-6-phosphate

Question 12

What enzyme converts G1P to G6P?

Answer 12

Phosphoglucomutase

Question 13

What is G6P converted into?

Answer 13

Glucose

Question 14

What enzyme converts G6P to glucose?

Answer 14

Glucose-6-phosphatase

Question 15

Where is glucose-6-phosphatase found?

Answer 15

Liver
Kidney
Intestine
(not in muscle)

Question 16

List the molecules in order of glycogenolysis

Answer 16

Glycogen
Glucose-1-phosphate
Glucose-6-phosphate
Glucose

Question 17

List the enzyme in order of glycogenolysis

Answer 17

Glycogen phosphorylase

Phosphoglucomutase

Glucose-6-phosphatase

Question 18

How does glycogen phosphorylase convert glycogen to glucose-1-phosphate?
(3)

Answer 18

It catalyses the sequential removal of glucose residues from non-reducing ends of glycogen chains (a1->4) bonds

It stops 4 residues from branch point (a1->6) glucosidic bond leaving limit dextrin

Limit dextrin is further degraded by debranching enzymes

Question 19

How does glycogen phosphorylase convert glucose-1-phosphate to glucose-6-phosphate?
(3)

Answer 19

This is a rate controlling step in glycogen breakdown

Two forms:
- phosphorylase a (phosphorylate/active form)
- phosphorylase b (dephosphorylated/less active form)

Question 20

What are the two debranching enzymes?

Answer 20

Glucanotransferase

Amylo-1,6-glucosidase

Question 21

What does glucanotransferase do?

Answer 21

It catalyses the relocation of a chain of 3 glucose from a branch to a free OH end of glycogen

Question 22

What does amylo-1,6-glucosidase do?

Answer 22

Catalyses the hydrolytic removal of remaining alpha (1->6) linked glucose

Question 23

What are the produces of the two debranching enzymes?

Answer 23

1 free glucose + chain (substrate for glycogen phosphorylase)

Question 24

Where is glycogen stored

Answer 24

Liver
Muscle

Question 25

What does the liver do when there is low blood glucose?

Answer 25

This triggers glycogen breakdown to G6P that is hydrolysed to glucose and supplies in the blood stream

Question 26

What does muscle do when there is low blood glucose?

Answer 26

Muscle needs ATP for movement and converts glycogen to G6P for glycolysis

Question 27

What happens when liver glucose increases?

Answer 27

Glycogen phosphorylase decreases Glycogen synthase increases

Question 28

What regulates the activity of Glycogen phosphorylase and glycogen synthase?

Answer 28

Phosphorylation/dephosphorylation

Question 29

What main hormone promotes glycogenolysis in muscle?

Answer 29

Adrenaline/Noradrenaline

Question 30

What main hormone promotes glycogenolysis in liver?

Answer 30

Glucagon

Question 31

How does a hormone activate glycogenolysis? (6)

Answer 31

The hormone binds at the membrane cAMP is synthesised cAMP activates protein kinase (PK) PK catalyses phosphorylation of phosphorylase b kinase (PBK) PBK catalyses phosphorylation of phosphorylase b to a Phosphorylase a catalyses glycogen breakdown

Question 32

What does cAMP do?

Answer 32

Activates protein kinase

Question 33

What does protein kinase do?

Answer 33

Catalyses the phosphorylation of phosphorylase b kinase (PBK)

Question 34

What does phosphorylase b kinase do?

Answer 34

Catalyses the phosphorylation of phosphorylase b to a

Question 35

What does phosphorylase a do?

Answer 35

Catalyses glycogen breakdown

Question 36

What does the glycogenolysis cascade depend on? (2)

Answer 36

Intracellular calcium cAMP levels

Question 37

What is calmodulin?

Answer 37

A calcium modulating protein with 4 calcium binding sites

Question 38

Name two other proteins involved in the glycogenolytic cascade

Answer 38

Calmodulin Phosphorylase b kinase multisubunits

Question 39

What three other nonhormonal ways are there to control glycogenolysis?

Answer 39

Glycogen phosphorylase Allosteric inhibitors Allosteric activators

Question 40

Name two allosteric inhibitors of glycogenolysis?

Answer 40

ATP Glucose-6-phosphate

Question 41

Name an allosteric activator of glycogenolysis

Answer 41

AMP

Question 42

What two hormones stimulate the breakdown of glycogen?

Answer 42

Adrenalin Glucagon

Question 43

What hormone stimulates the synthesis of glycogen?

Answer 43

Insulin

Question 44

What does the breakdown of glycogen result from?

Answer 44

Kinase cascade

Question 45

Where is GLUCAGON made?

Answer 45

Alpha cells of islets of langerhans in the pancreas These cells sense blood glucose and release hormones in response to low levels

Question 46

What does glucagon do?

Answer 46

It increases liver cAMP so that metabolic cascades promote glycogenolysis This also inhibits glycogen synthase

Question 47

What is the main energy source for resting muscle?

Answer 47

Fatty acids

Question 48

What is the main energy source for exerted muscle?

Answer 48

Glucose Early exertion (glucose from muscle's glycogen reserves) Late exertion (glucose from fatty acid reserves)

Question 49

How does adrenaline work in muscle (3)

Answer 49

Adrenaline activates adenylate cyclase It activates glycogenolysis and the inhibition of glycogen synthesis Promotes glycogen mobilisation

Question 50

How does glucagon affect the liver?

Answer 50

Stimulates synthesis of cAMP by membrane bound adenylate cyclase through action of a G protein

Question 51

What are the two types of receptors for epinephrine?

Answer 51

B adrenergic receptors A adrenergic receptors

Question 52

What are B adrenergic receptors linked to?

Answer 52

To the adenylate cyclase system

Question 53

What are a adrenergic receptors?

Answer 53

Receptors whose second messenger causes intracellular Ca2+ to increase

Question 54

What type of adrenergic receptors do muscles have?

Answer 54

Beta

Question 55

What does increased intracellular Ca2+ do?

Answer 55

It reinforces cells response to cAMP