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NE > Glycogen Metabolism > Flashcards

Glycogen Metabolism Flashcards

1
Q

What is glycogen?

A

Large homopolymer of glucose, highly branched, insoluble, acts as carb energy store

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2
Q

What is the glycogen structure?

A

residues linked by a-1,4 glycosidic bonds 93% and a-1,6 g bonds 7%

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3
Q

How often does glycogen branch?

A

every 10 or so residues via a-1,6, glycosidic bonds

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4
Q

What is the benefits of branching?

A

Improves solubility and more sites available for synthesis and degradation interactions (rapid breakdown)

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5
Q

What are the main tissues that store glycogen?

A

Liver and muscle

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6
Q

What does liver do with glycogen?

A

Maintains blood glucose, release over long periods of time

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7
Q

What does muscle do with glycogen?

A

energy provision for muscle, released when required

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8
Q

What is the function of glycogen?

A

Energy reserve, readily made - mobilised

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9
Q

how is glycogen stored?

A

In granules that contain not only glycogen but enzymes and regulatory protein for synthesis

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10
Q

What is glucostat?

A

maintains constant blood glucose levels in spite of spisodic nature of food intake and fasting and flunctuations in energy demand

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11
Q

How does Glycogen sort fight or flight response into?

A

adrenaline stimulates glycogen breakdown to increase blood sugar levels and energy

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12
Q

what does glycogen synthesis require?

A

Energy

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13
Q

What is the activated form of glucose?

A

UPD-Glucose

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14
Q

How many moles of ATP used for per moles of UPD glucose?

A

2 moles

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15
Q

What is process of UPD-glucose to glucose 1-p by?

A

UDP-glucose pyrophosphorylase

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16
Q

What is glucosyl residue from UDP-glucose transferred to?

A

C-4OH group at non-reducing end of glycogen

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17
Q

What does glucosyl and C-4OH form?

A

a-1,4, glycosidic bond

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18
Q

What can glycongen synthase extend?

A

Existing chain

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19
Q

What primer is used for the enzyme to extend the chain?

A

glycogenin

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20
Q

What is glycogen synthesized by?

A

Glycogen synthase

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21
Q

What does the synthesis require?

A

branches to be made every 10 residues- branching enzymes

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22
Q

How is a 1-6 branch point formed?

A

10 glucose units added to glycogen

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23
Q

What does the branching enzyme do?

A

Breaks an a-1,4 bond and transfers block of 7 residues to interior site of glycogen molecule

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24
Q

How are the bonds re-attached?

A

a-1-6 bond

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25
Q

what 3 enzymes are needed to synthesize glycogen?

A

UDP-glucose pyrophosphorylase
Glycogen synthase
Branching enzyme (amylo-transglycosylase)

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26
Q

What does catabolic process of glycogen result in?

A

Formation of free glucose or glucose-6-phosphate

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27
Q

What does glycogen phosphorylase do?

A

Degrades glycogen by breaking a-1,4, glycosidic bonds to release glucose units one at a time from end with free 4-OH group

28
Q

What does phospohorylsisdo?

A

Use organic phosphate

29
Q

What is glucose released as?

A

Glucose 1-phosphate

30
Q

When is breakdown of glycogen rapid?

A

Through cascade mechanism

31
Q

What is glycogen presence aided by?

A

Multiple branch points

32
Q

How many glucose-1-phosphate residues released and when?

A

7-9 for every branch point

33
Q

When can glycogen phosphorylase remove glucose residues?

A

> 5 away from branchpoint

34
Q

What happens to the remaining residues?

A

Added to an existing chain with an a-1,4 glycosidic bond - catalysed by transferase

35
Q

What happens with the residue at the a-1,6 branching point?

A

Removed with glycogen-debranching enzyme

36
Q

What are the 3 enzymes required to break down glycogen?

A

Glycogen phosphorylase, transferase enzyme, glycogen-debranching enzyme

37
Q

What is G1-P converted to? and by what enzyme?

A

glucose-6-phosphate by phosphoglucomutase

38
Q

What does liver contain that muscle does not?

A

glucose-6-phosphate , so free glucose formed and released for export

39
Q

What does muscle not contain G-6-P?

A

Used locally in glycolysis

40
Q

What is glycogenesis?

A

Synthesis

41
Q

What is glycogenolysis?

A

Breakdown

42
Q

Why can glycogenesis and glycogenolysis not occur at same time?

A

Prevents hydrolysis of UTP via substrate cycle

43
Q

How is glycogenesis and glycogenolysis controlled?

A

allosteric regulation
covalent modificatio of phosphorylase and synthase enzymes
hormonal control by adrenaline, glucagon and insulin

44
Q

What does allosteric regulation of glycogen phosphorylase in skeletal muscle do?

A

High amp activate phos b - opposed by high atp and G-6-p, exercise balance changes, amp activates phos b

45
Q

What is phosphorylse a not affected by?

A

ATP, AMP, Glu-6

46
Q

What does allosteric regulation of glycogen phosphorylase in liver do?

A

phos b not regulated by amp so inactive and not responsive to energy in cell, phos a deactivated by glucose

47
Q

What does high glu-6-p activate?

A

Glycogen synthase b

48
Q

When is glu-6-p low?

A

During muscle contraction - favours phosphorylase activation

49
Q

What is glycogen synthase?

A

active regardless of glu-6-p levels

50
Q

Which hormones reduce glycogen synthase activity?

A

adrenaline and glycogen

51
Q

What do these hormones stimulate?

A

glycogen breakdown by activating glycogen phosphorylase

52
Q

What does insulin stimulate?

A

glycogen synthase activity

53
Q

What does insulin reduce?

A

glycogen phosphorylase activity

54
Q

Where is glucagon secreted and act on?

A

a-cells in pancreas

acts on liver to stimulate glycogen breakdown to glucose

55
Q

Where is glucose release?

A

in bloodstream

56
Q

What hormones causes glycogen breakdown?

A

adrenaline

57
Q

What causes glycogen breakdown in the muscles?

A

Adrenaline

58
Q

What receptor does adrenaline bind to?

A

B-adrenergic receptor on PM of target cell

59
Q

What pathway does adrenaline work on?

A

G-protein - bind 2 cAMP molecules to PKA to make it active

60
Q

What does phos b convert to?

A

phos a - degrades glycogen

61
Q

What amplifies the response of glycogen release?

A

Cascade

62
Q

When turns off activation cascade?

A

decline in cAMP - dephosphorylation restores enzymes

63
Q

What does insulin act on?

A

liver to stimulate glycogen synthesis from glucose

64
Q

What is insulin used for?

A

dephosphorylation of enzymes, glycogen synthase on, glycogenesis

65
Q

What does glucagon act on?

A

Phosphorylation of enzymes , glycogen synthase off, glycogenolysis

NE (17 decks)

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