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MABS Biochemistry > 34 Glycogen > Flashcards

34 Glycogen Flashcards

1
Q

humans consume how many grams of glucose per day?

A

160 g of glucose per day

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2
Q

how many grams of glucose does the blood carry at homeostasis?

A

the blood carries only about 4 g glucose at homeostasis

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3
Q

what percent of glucose is used by the brain?

A

75% of glucose is used by the brain

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4
Q

how many grams of glycogen is stored by the liver?

A

100-120 g glycogen

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5
Q

what is the main agent that monitors and controls the blood glucose level?

A

the liver

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6
Q

in terms of glycogen, what determines liver action?

A

Liver is directed by insulin and glucagaon

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7
Q

after a mean what hormone is stimulated and what happens to excess glucose?

A

insulin; excess glucose is stored as glycogen in liver.

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8
Q

what happens to the additional excess glucose?

A

the excess glucose is converted to FAs and TG in the liver and exported to adipose tissue for storage.

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9
Q

*so what happens to the glycogen in between meals, like fasting?

A

liver glycogen is degraded to glucose to be released into the bloodstream to maintain blood glucose. Large supply of glycogen allows liver to regulate blood glucose for ~18 hours

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10
Q

how much glycogen can be store in the muscle?

A

300-340 g of glycogen

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11
Q

how does the muscle use glycogen?

A

it keeps the glycogen for its own use (not released to blood)

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12
Q

how does muscle react under insulin?

A

muscle accumulates glucose for energy – but also stores glucose as glycogen

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13
Q

*what is the purpose of muscle glycogen?

A

is used to support muscle metabolism at all times, fasting or fed. Large amount of glycogen in fast twitch muscles to support fast-twitch function. Less in slow twitch muscles, but still there.

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14
Q

how long will the glycogen stored by the liver last? how long before its totally gone? what does glycogen provide?

A

12-24 hour supply of glycogen for use during fasting; by 30 hours of fasting it’s totally gone; it provides individual glucose residues to be released into the blood

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15
Q

what is provided when muscle glycogen is degraded? how long does this last for light activity? intense activity?

A

to provide glucose 6-phosphate for anaerobic glycolysis to support muscle contraction / ATP demands; lasts minutes to hours during light activity
and seconds during high intensity activity

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16
Q

T/F, muscle metabolizes glycogen much more rapidly than fatty acids?

A

true and anaerobically

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17
Q

are fatty acids a major source of energy for muscle?

A

yes, especially cardiac and slow twitch muscles

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18
Q

what does the liver use as a source of glucose?

A

glycogen and will not use glucose under these conditions and during times of fasting the liver can use fatty acids for energy to support function during fasting

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19
Q

what is the structure of glycogen?

A

Branched glucose polysaccharide

Only one residue has a reducing end: attached to glycogenin protein

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20
Q

how are the glucose molecules attached in the glycogen molecule?

A

glucosyl units linked by α-1,4 glycosidic bonds with α-1,6 branches every 8-10 residues

present in all tissues as very high molecular weight polymers (107 – 108 g/mol)

collected together in glycogen particles

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21
Q

what significance does the branched structure of glycogen serve?

A

tight packing of glucose

rapid degradation and rapid synthesis

enzymes can work on several branches at the same time

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22
Q

how are enzymes involved with glycogen?

A

synthesis
degradation
regulatory enyzmes attached to surface of glycogen particles

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23
Q

can our bodies digest the alpha-1,4 linkage? what about the beta-1,4 linkage?

A

yes; no

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24
Q

what is the name of the molecule that makes up the core of the glycogen?

A

glycogenin and then the glucose attach

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25
Q

what is glycogen degraded too?

A

glucose-1-phosphate which is converted to glucose-6- phosphate which is then fed into glycolysis

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26
Q

do fast twitch skeletal muscle have a lot of mitochondria?

A

no, so pyruvate begins to build up and so it converts this into lactate and ships it out

27
Q

what process are we looking at when we see CO2?

A

most likely the TCA cycle

28
Q

what enzyme does the liver have that converts glucose-6-phosphate to glucose in order to send it out into the blood? does skeletal muscle have this?

A

it has the enzyme glucose-6-phosphatase, which produces free glucose and then released out into the blood; during gluconeogenesis, glycolysis is down regulated

no, because it G-6-P does not need to be processed

29
Q

what is key for glycogen synthesis?

A

the formation of α-1,4-glycosidic bonds to link glucose residues in long chains, and the formation of an α-1,6 branch every 8-10 residues

30
Q

what is the site of attachment in glycogen synthesis?

A

the non-reducing free ends of the molecule

31
Q

what is the reducing end attached too for glycogen?

A

glycogenin

32
Q

glucose phosphorylated to form this by this enzyme in the liver?

A

glucose 6-phosphate by hexokinase (glucokinase in liver) as it enters the cell which is converted to glucose 1-phosphate in preparation for attachment to glycogen; note that for muscle, glucose is in G-6-P form and so it feeds into glycolysis

33
Q

what is unique about liver glycogen?

A

the largest store of glycogen in the body and broken down to supply glucose units to the blood for other tissues to use like the brain and RBCs

34
Q

what does glucagon signaling activate in the liver?

A

glycogenolysis

35
Q

Epinephrine/norepinephrine signaling also activates this in the liver?

A

glycogenolysis

36
Q

in the liver, how is glycogen liberated, starting with glucose-6-phosphate?

A

6-phosphate liberated during glycogen breakdown is converted to glucose by glucose 6-phosphatase (present only in liver and kidneys)

37
Q

in the liver, when is glucose readily released?

A

readily released in response to lower levels or increased need due to exercise, etc.

38
Q

T/F, in the liver glycogen degradation or glycogenolysis is tied directly to the activation of gluconeogenesis (production of glucose from dietary fuels).

A

T

39
Q

T/F, in the liver Gluconeogenesis also produces glucose 6-phosphate.

A

T

40
Q

T/F, in the liver Glycolysis also linked to pentose phosphate pathway, and synthesis of other sugars, which intersect at glucose 6-phosphate

A

T

41
Q

in the muscle, what is glycogen broken down too?

A

glucose 1-phosphate by (glycogen phosphorylase) which is converted to glucose 6-phosphate

42
Q

T/F, skeletal muscle also has glucose-6-phosphatase so it can generate free glucose and enter into the blood stream?

A

F, it does not and therefore glucose cannot enter the blood stream directly

43
Q

so in the muscle, what happens to the glucose-6-phosphate?

A

it enters the glycolytic pathway to make ATP within the cell

44
Q

in the muscle, what is the major signal that activate glycogen degradation in muscle?

A

AMP

45
Q

is muscle responsive to glucagon?

A

no

46
Q

in the muscle, is epi/norepi a major activator of glycogenolysis?

A

yes

47
Q

what is the state of glucagon vs insulin when you have low blood glucose levels?

A

glucagon is high and insulin is low

48
Q

since we know that glucagon signals the fasting state, what does this do to glycogen breakdown and synthesis? describe the activity of the enzyme involved

A

this stimulates glycogen breakdown in which Glycogen phosphorylase is phosphorylated by cAMP-dependent PKA

this shuts down glycogen synthesis in which glycogen synthase is phosphorylated which means it is inhibited

49
Q

what happens after a high carbohydrate mean? the activity of insulin?

A

blood glucose will increase, Insulin will be released – high insulin to glucagon ratio

50
Q

when glucagon signaling stops what enzyme is inhibited? so as a result insulin would be active, what enzyme is activated?

A

PKA activity inhibited; Insulin signaling activates protein phosphatase 1 which reverses the effects of PKA and so glycogen phosphorylase is inhibited and glycogen synthase is activated

51
Q

what is the effect of glucagon on PKA? what about insulin?

A

it stimulates PKA which phosphorylates both glycogen phosphorylase (ON) and glycogen synthase (OFF)

Insulin activates phosphatases, which reverse the phosphorylation effects.

glycogen phosphorylase B goes to glycogen phosphorylase A

glycogen synthase I or A goes to glycogen synthase D or B

52
Q

during exercise, do muscles require lots of ATP?

A

yes, and so lots of energy is required to keep ATP production going

53
Q

during exercise since we use ATP and this degraded to ADP, how is this converted to AMP?

A

adenylate kinase, and so AMP is the signal for mobilization of glycogen stores

54
Q

what is the effect of AMP on the glycogen? what happens as AMP levels continue to increase?

A

AMP is an allosteric activator and so as AMP levels rise, this signals the need for more ATP, hence glucose, resulting in increased enzyme activity.

The presence of AMP makes the inactive form of glycogen phosphorylase (phosphorylase b) more active w/o phosphorylation

55
Q

what are the two major control mechanisms for glycogen phosphorylase activity?

A

AMP, which is produced by muscle metabolism (normal mechanism)

Phosphorylation, which IN MUSCLE is stimulated by catecholamines

56
Q

how is calmodulin activated?

A

a calcium sensor; When Ca2+ is low, the protein does not bind Ca2+ and is inactive. When Ca2+ concentration increases, Ca2+ ions bind to CAM and induce a conformational change in CAM to the activated form. Activated CAM can bind to a variety of target proteins to alter their activity. One protein is the phosphorylase kinase.

57
Q

since it is possible for glycogen particles to become trapped in transport vesicles that fuse with lysosomes, how is this remediated? (hint, what is the enzyme?)

A

lysosomal glucosidase can hydrolyze glycogen to glucose

58
Q

what is the name of the disease when there is a genetic defect in lysosomal glucosidase?

what does this do?

A

type II glycogen storage disease

prevents it from functioning
glycogen particles build up in vesicles
disrupts heart and liver function.

59
Q

what are glycogen storage disease?

A

The inability to synthesize or breakdown glycogen by normal mechanisms.

60
Q

how are glycogen storage diseases classified?

A

Classified by number according to which enzyme is deficient.

O, I, III, IV, VI affect the liver
V and VII affect skeletal muscle

61
Q

what is the result of glycogen storage disease?

A

End result is that patient’s liver will not be able to produce glucose units for release into blood = hypoglycemia during times of fasting

or

skeletal muscle will not get the glucose it needs to support function = cramps due to low energy.

62
Q

what is the therapy for glycogen storage disease affecting the liver?

A

For liver-based forms, the therapy is to have patient maintain proper blood glucose level through diet. Small glucose snacks at regular intervals.

63
Q

what is the therapy for glycogen storage disease affecting skeletal muscle?

A

For skeletal muscle-based forms: therapy is to reduce exercise and muscle fatigue to avoid painful muscle cramps. Or to supplement with higher dietary glucose and amino acids.

MABS Biochemistry (54 decks)

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