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Biochemistry Exam 2 > Lecture 23: Glycogen Metabolism II > Flashcards

Lecture 23: Glycogen Metabolism II Flashcards

1
Q

What are the rate limiting enzymes of synthesis and degradation?

A

synthesis: glycogen synthase
degradation: glycogen phosphorylase

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2
Q

What are the two forms of glycogen synthase?

A

active non phosphorylated ‘a’ form

inactive phosphorylated ‘b’ form

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3
Q

What is the most important kinase that phosphorylates glycogen synthase?

A

glycogen synthase kinase (GSK)

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4
Q

What is GSK under the control of?

A

insulin and PKA

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5
Q

What are the two forms of glycogen phosphorylase?

A

active ‘a’ form (R relaxed state)

inactive ‘b’ form (T tense state)

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6
Q

Where is the active a form found?

A

in liver

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7
Q

Where is the inactive b form found?

A

in muscle

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8
Q

What is glycogen phosphorylase regulated by?

A

several allosteric effectors

reversible phosphorylation

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9
Q

mutation in liver glycogen phosphorylase causes ____

A

Hers disease

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10
Q

mutation in muscle glycogen phosphorylase causes ____

A

McArdle syndrome

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11
Q

Describe allosteric regulation of liver glycogen phosphorylase

A

in default active a form
made inactive by glucose
glucose bind to active site and stabilizes confirmation in the inactive T state
this is because when glucose levels are high, there is no need to breakdown glycogen

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12
Q

describe allosteric regulation of muscle glycogen phosphorylase

A

in default inactive b form
activated by AMP
binds to active site and stabilizes conformation of b in the active R state
during muscle contraction ATP converted to AMP by myosin and adenylate kinase signaling the GP to breakdown glycogen

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13
Q

What are negative allosteric regulators of muscle glycogen phosphorylase

A

ATP and gluc-6-phosphate

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14
Q

glycogenesis is favored in ____ state

A

fed

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15
Q

What is the fed state?

A

blood glucose high
insulin high
cellular ATP high

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16
Q

glycogenolysis is favored in the ____ state ( and during ____)

A

fasting; exercise

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17
Q

what is the fasting state?

A

blood glucose low

glucagon high

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18
Q

What is high during exercise?

A

cellular calcium

AMP

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19
Q

What do beta cells release in the pancreas?

A

insulin

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20
Q

what are the four key proteins involved in regulation by insulin

A

GLUT 4
protein kinase B (PKB)
protein phosphatase 1 (PP1)
glycogen synthase kinase 3 (GSK3)

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21
Q

What is the net result of insulin regulation?

A

glycogen synthesis via activation of glycogen synthase and inactivation of glycogen phosphorylase

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22
Q

What causes type 2 diabetes?

A

reduced sensitivity to insulin ( insulin resistance)

usually caused by mutations in insulin receptor and/or downstream signaling proteins

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23
Q

What is considered normal blood glucose?

A

70-100 mg/dL (fasting)

< or = to 140 mg/dL (fed)

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24
Q

What is considered prediabetic/at risk blood glucose?

A

100-125 mg/dL (fasting)

> 140 mg/dL (fed)

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25
Q

What is considered diabetes mellitus blood glucose levels?

A

> or = to 126 mg/dL (fasting)

> or = to 199 mg/dL (fed)

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26
Q

low blood sugar levels release ____

A

glucagon

27
Q

phosphorylation of a single serine does what? What is the conversion initiated by?

A

converts b to a

initiated by hormones

28
Q

What is phosphorylation carried out by?

A

phosphorylase kinase

29
Q

when epinephrine is released by adrenal glands, what occurs?

A

promotes degradation of glycogen

30
Q

How does glucose 6 phosphate work as an allosteric regulator?

A

activates glycogen synthase, inactivates glycogen phosphorylase

31
Q

How does free glucose work as an allosteric regulator?

A

inhibits glycogen phosphorylase in liver but not muscle

32
Q

How does Ca2+ work as an allosteric regulator?

A

activates glycogen phosphorylase kinase

33
Q

How does AMP work as an allosteric regulator?

A

activates glycogen phosphorylase (especially relevant during periods of exercise)

34
Q

Type I (von Gierke) defective enzyme

A

glucose 6 phosphatase or transport system

35
Q

Type I (von Gierke) organ affected

A

liver and kidney

36
Q

Type I (von Gierke) glycogen in affected organ

A

increased amount; normal structure

37
Q

Type II (Pompe) defective enzyme

A

a-1,4-glucosidase (lysosomal)

38
Q

Type II (Pompe) organ affected

A

all organs

39
Q

Type II (Pompe) glycogen in affected organ

A

massive increase in amount; normal structure

40
Q

Type III (cori) defective enzyme

A

a-1,6-glucosidase (debranching enzyme)

41
Q

Type III (cori) organ affected

A

muscle and liver

42
Q

Type III (cori) glycogen in the affected organ

A

increased amount, short outer branches

43
Q

type IV (andersen) defective enzyme

A

branching enzyme (a-1,4 to a-1,6)

44
Q

type IV (andersen) organ affected

A

liver and spleen

45
Q

type IV (andersen) glycogen in affected organ

A

normal amount, very long outer branches

46
Q

type V (McArdle) defective enzyme

A

phosphorylase

47
Q

type V (McArdle) organ affected

A

muscle

48
Q

type V (McArdle) glycogen in affected organ

A

moderately increased amount, normal structure

49
Q

type VI (Hers) defective enzyme

A

phosphorylase

50
Q

type VI (Hers) organ affected

A

liver

51
Q

type VI (Hers) glycogen in affected organ

A

increased amount

52
Q

type VII defective enzyme

A

phosphofructokinase

53
Q

type VII organ affected

A

muscle

54
Q

type VII glycogen in affected organ

A

increased amount, normal structure

55
Q

type VIII defective enzyme

A

phosphorylase kinase

56
Q

type VIII organ affected

A

liver

57
Q

type VIII glycogen in the affected organ

A

increased amount, normal structure

58
Q

What is GSD 0?

A

deficiency in glycogen synthase, patients cannot synthesize glycogen

have muscle cramps, rely on glucose in diet, need to eat frequently and vulnerable to hypoglycemia when fasting

59
Q

What is a symptom in GSD III/Cori disease

A

light hypoglycemia and hepatomegaly

60
Q

What are symptoms of GSD IV/ Andersen disease

A

enlargement of liver and spleen, scarring of liver tissue

death by 5 years of age

61
Q

What are symptoms in GSD V/ McArdle disease

A

patients unable to supply muscles with enough glucose
weakness, muscle cramps, exercise intolerance
myoglobinuria (myoglobin in urine)
tolerance by reducing strenuous exercise

62
Q

GSD VI/ hers disease symptoms

A

prevents glycogen breakdown in liver, accumulates there and causes hepatomegaly
low blood glucose levels

63
Q

how can enzyme replacement therapy (ERT) treat Pompe disease (GSD III)

A

GSD II is defect in acid maltase (a-glucosidase) which causes accumulation of glycogen in lysosomes and disrupts function of music end liver cells, causing progressive muscle weakness and myopathy ending with death via heart failure
ERT: Recombinate human a- glucosidase delivered via intravenous infusion in babies/young children

Biochemistry Exam 2 (12 decks)

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