[2] Lecture 8: Glycogen Metabolism Flashcards Preview

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Flashcards in [2] Lecture 8: Glycogen Metabolism Deck (87)
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31

Liver GP is inactivated and moves to tense states under what conditions?

Fed-state

32

Major inactivator of Liver (a) GP?

Glucose!

Glu binds to active site and stabilizes conformation in the inactive T state.

Makes sense...when BG levels are high, there's no need for glycogen breakdown.

33

Muscle GP (b) is activated under what conditions?

Low energy states

Activated by AMP...

This makes sense b/c muscle contraction ATP converted to AMP by myosin and adenylate kinase signaling the GP to breakdown glycogen

34

AMP GPb activator mechanism:

Binds to active site and stabilizes conformation of the b in the active R state

35

What are 2 negative allosteric regulator (inhibitors) of GP b (muscle)?

ATP and gluc-6-phosphate

Under norm physiological conditions GP inactive b/c of inhibitory effect of ATP and Gluc-6-phosphate

36

What role does phosphorylation play in glycogen phosphorylase?

How is it initiated?

Phosphorylation of a single serine residue converts GP b to GP a

Conversion initiated by hormones

37

Phosphorylation of GP is carried out by what enzyme,?

Phosphorylase kinase (PK)

38

How is phosphorylase kinase partially activated?

Fully activated?

4 Ca++ ions partially activate PK

4 Ca++ ions and 8 Phosphates fully activates PK

39

What results when Pohsphoylase kinase is fully active?

Phosophorylase b converts to phosphorylase a

But requires 2 ATP

40

Wha hormone is released under low [BG] conditions

Glucagon

41

Muscle activity releases what hormone?

Epinephrine

42

Glucagon and epinephrine are mediated via:

Both of these hormones signal:

via G protein coupled receptors (GPCR)

Signal glycogen breakdown

43

Glucagon and epinephrine, can they pass the plasmalemma?

No they are peptide hormones that act on the GPCR's

44

When does glycogen breakdown stop?

When the hormone (glucagon or Epi) shuts down

PK and GP are DEphosphorylated =inactivated

When synthesis of glycogen is promoted

45

Liver and muscle forms of GP are products of separate genes what is this term called?

Isozymes

46

Liver vs. muscle GP

DIFFER: in their sensitivities to regulatory molecules

Both are activated by phosphorylation by phosphorylase kinase and inhibited by ATP and G6P

47

Muscle GP is allosterically activated by

AMP

48

Liver GP is inactivated by:

Unaffected by:

Inactivated by glucose and unaffected by AMP

49

Mutations in liver GP causes

Hers disease

50

Mutaiton in muscle GP causes:

McArdle syndrome

51

3 key events in glycogenesis:

1. Trapping and activating of glucose.
2. Elongation of glycogen polymer
3. Branching of glycogen chains.

52

In the cytosol of hepatocytes and muscle cells catalyze phosphorylation of glucose to glucose-6-phosphate.

This traps glucose in theses cells.

Glucokinase / hexokinase

53

Reversible isomerizes G-6-P to G-1-P

Phosphoglucomutase

54

Transfers the G-1-P to uridine triphosphate which generates UDP-glucose

Uridine diphosphate (UDP)-glucose pyrophosphorylase

55

Active form of glucose

UDP-glucose

56

What is the significance of the Breakdown of pyrophosphate to Pi w/ UTP and glycogenesis?

generates energy and drives the RXN forward

57

Preexisting short glycogen polymer serves as a primer to which glucose units are added

Primer formation done by glycogenin

This is completed by the transfer of glucose from UDP-glucose onto a non-reducing end of glycogen chain. What enzyme comlpletes this?

Glycogen synthase

58

Rate limiting rx of glycogenesis

Glycogen synthase

59

Forms alpha-1,4-glycosidic bonds btw glucose molecules.

Glycogen synthase

60

Glycogenin requires

Manganese-Mn