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2.1 Biochemistry of Metabolism > Brenda - Glycogenolysis > Flashcards

Brenda - Glycogenolysis Flashcards

1
Q

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

A

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

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2
Q

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

A

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

This allows for production of more glucose by gluconeogenesis

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3
Q

Write a note on starch
(3)

A

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)

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4
Q

Write a note on glycogen
(3)

A

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

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5
Q

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

A

Glycogen synthesis

Glycogen breakdown

Both are regulated to maintain blood glucose levels

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6
Q

What is the function of glycogen in the muscle?

A

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

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7
Q

What is glycogenolysis?

A

The degradation of stored glycogen

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8
Q

What enzyme degrades glycogen?

A

Glycogen phosphorylase

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9
Q

How does glycogen phosphorylase degrade glycogen?

A

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

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10
Q

What product is formed from the degradation of glycogen?

A

Glucose1Phosphate

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11
Q

What is G1P converted into ?

A

Glucose-6-phosphate

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12
Q

What enzyme converts G1P to G6P?

A

Phosphoglucomutase

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13
Q

What is G6P converted into?

A

Glucose

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14
Q

What enzyme converts G6P to glucose?

A

Glucose-6-phosphatase

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15
Q

Where is glucose-6-phosphatase found?

A

Liver
Kidney
Intestine
(not in muscle)

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16
Q

List the molecules in order of glycogenolysis

A

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

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17
Q

List the enzyme in order of glycogenolysis

A

Glycogen phosphorylase

Phosphoglucomutase

Glucose-6-phosphatase

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18
Q

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

A

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

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19
Q

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

A

This is a rate controlling step in glycogen breakdown

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

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20
Q

What are the two debranching enzymes?

A

Glucanotransferase

Amylo-1,6-glucosidase

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21
Q

What does glucanotransferase do?

A

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

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22
Q

What does amylo-1,6-glucosidase do?

A

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

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23
Q

What are the produces of the two debranching enzymes?

A

1 free glucose + chain (substrate for glycogen phosphorylase)

24
Q

Where is glycogen stored

A

Liver
Muscle

25
Q

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

A

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

26
Q

What does muscle do when there is low blood glucose?

A

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

27
Q

What happens when liver glucose increases?

A

Glycogen phosphorylase decreases

Glycogen synthase increases

28
Q

What regulates the activity of Glycogen phosphorylase and glycogen synthase?

A

Phosphorylation/dephosphorylation

29
Q

What main hormone promotes glycogenolysis in muscle?

A

Adrenaline/Noradrenaline

30
Q

What main hormone promotes glycogenolysis in liver?

A

Glucagon

31
Q

How does a hormone activate glycogenolysis?
(6)

A

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

32
Q

What does cAMP do?

A

Activates protein kinase

33
Q

What does protein kinase do?

A

Catalyses the phosphorylation of phosphorylase b kinase (PBK)

34
Q

What does phosphorylase b kinase do?

A

Catalyses the phosphorylation of phosphorylase b to a

35
Q

What does phosphorylase a do?

A

Catalyses glycogen breakdown

36
Q

What does the glycogenolysis cascade depend on?
(2)

A

Intracellular calcium

cAMP levels

37
Q

What is calmodulin?

A

A calcium modulating protein with 4 calcium binding sites

38
Q

Name two other proteins involved in the glycogenolytic cascade

A

Calmodulin

Phosphorylase b kinase multisubunits

39
Q

What three other nonhormonal ways are there to control glycogenolysis?

A

Glycogen phosphorylase

Allosteric inhibitors

Allosteric activators

40
Q

Name two allosteric inhibitors of glycogenolysis?

A

ATP

Glucose-6-phosphate

41
Q

Name an allosteric activator of glycogenolysis

A

AMP

42
Q

What two hormones stimulate the breakdown of glycogen?

A

Adrenalin

Glucagon

43
Q

What hormone stimulates the synthesis of glycogen?

A

Insulin

44
Q

What does the breakdown of glycogen result from?

A

Kinase cascade

45
Q

Where is GLUCAGON made?

A

Alpha cells of islets of langerhans in the pancreas

These cells sense blood glucose and release hormones in response to low levels

46
Q

What does glucagon do?

A

It increases liver cAMP so that metabolic cascades promote glycogenolysis

This also inhibits glycogen synthase

47
Q

What is the main energy source for resting muscle?

A

Fatty acids

48
Q

What is the main energy source for exerted muscle?

A

Glucose

Early exertion (glucose from muscle’s glycogen reserves)

Late exertion (glucose from fatty acid reserves)

49
Q

How does adrenaline work in muscle
(3)

A

Adrenaline activates adenylate cyclase

It activates glycogenolysis and the inhibition of glycogen synthesis

Promotes glycogen mobilisation

50
Q

How does glucagon affect the liver?

A

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

51
Q

What are the two types of receptors for epinephrine?

A

B adrenergic receptors

A adrenergic receptors

52
Q

What are B adrenergic receptors linked to?

A

To the adenylate cyclase system

53
Q

What are a adrenergic receptors?

A

Receptors whose second messenger causes intracellular Ca2+ to increase

54
Q

What type of adrenergic receptors do muscles have?

A

Beta

55
Q

What does increased intracellular Ca2+ do?

A

It reinforces cells response to cAMP

2.1 Biochemistry of Metabolism (21 decks)

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