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Glycogen Metabolism Flashcards

(65 cards)

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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
what 3 enzymes are needed to synthesize glycogen?
UDP-glucose pyrophosphorylase Glycogen synthase Branching enzyme (amylo-transglycosylase)
26
What does catabolic process of glycogen result in?
Formation of free glucose or glucose-6-phosphate
27
What does glycogen phosphorylase do?
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
What does phospohorylsisdo?
Use organic phosphate
29
What is glucose released as?
Glucose 1-phosphate
30
When is breakdown of glycogen rapid?
Through cascade mechanism
31
What is glycogen presence aided by?
Multiple branch points
32
How many glucose-1-phosphate residues released and when?
7-9 for every branch point
33
When can glycogen phosphorylase remove glucose residues?
>5 away from branchpoint
34
What happens to the remaining residues?
Added to an existing chain with an a-1,4 glycosidic bond - catalysed by transferase
35
What happens with the residue at the a-1,6 branching point?
Removed with glycogen-debranching enzyme
36
What are the 3 enzymes required to break down glycogen?
Glycogen phosphorylase, transferase enzyme, glycogen-debranching enzyme
37
What is G1-P converted to? and by what enzyme?
glucose-6-phosphate by phosphoglucomutase
38
What does liver contain that muscle does not?
glucose-6-phosphate , so free glucose formed and released for export
39
What does muscle not contain G-6-P?
Used locally in glycolysis
40
What is glycogenesis?
Synthesis
41
What is glycogenolysis?
Breakdown
42
Why can glycogenesis and glycogenolysis not occur at same time?
Prevents hydrolysis of UTP via substrate cycle
43
How is glycogenesis and glycogenolysis controlled?
allosteric regulation covalent modificatio of phosphorylase and synthase enzymes hormonal control by adrenaline, glucagon and insulin
44
What does allosteric regulation of glycogen phosphorylase in skeletal muscle do?
High amp activate phos b - opposed by high atp and G-6-p, exercise balance changes, amp activates phos b
45
What is phosphorylse a not affected by?
ATP, AMP, Glu-6
46
What does allosteric regulation of glycogen phosphorylase in liver do?
phos b not regulated by amp so inactive and not responsive to energy in cell, phos a deactivated by glucose
47
What does high glu-6-p activate?
Glycogen synthase b
48
When is glu-6-p low?
During muscle contraction - favours phosphorylase activation
49
What is glycogen synthase?
active regardless of glu-6-p levels
50
Which hormones reduce glycogen synthase activity?
adrenaline and glycogen
51
What do these hormones stimulate?
glycogen breakdown by activating glycogen phosphorylase
52
What does insulin stimulate?
glycogen synthase activity
53
What does insulin reduce?
glycogen phosphorylase activity
54
Where is glucagon secreted and act on?
a-cells in pancreas | acts on liver to stimulate glycogen breakdown to glucose
55
Where is glucose release?
in bloodstream
56
What hormones causes glycogen breakdown?
adrenaline
57
What causes glycogen breakdown in the muscles?
Adrenaline
58
What receptor does adrenaline bind to?
B-adrenergic receptor on PM of target cell
59
What pathway does adrenaline work on?
G-protein - bind 2 cAMP molecules to PKA to make it active
60
What does phos b convert to?
phos a - degrades glycogen
61
What amplifies the response of glycogen release?
Cascade
62
When turns off activation cascade?
decline in cAMP - dephosphorylation restores enzymes
63
What does insulin act on?
liver to stimulate glycogen synthesis from glucose
64
What is insulin used for?
dephosphorylation of enzymes, glycogen synthase on, glycogenesis
65
What does glucagon act on?
Phosphorylation of enzymes , glycogen synthase off, glycogenolysis

NE (17 decks)

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