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Biochemistry > [2] Lecture 8: Glycogen Metabolism > Flashcards

[2] Lecture 8: Glycogen Metabolism Flashcards

1
Q

Osmotically inactive, readily mobilized form of glucose.
12 layers of glu. W/ approx. 55,000 glucose residues.
Linked w/ alpha-1,4 glycosidic bonds and branched w/ alpha-1,6 glycosidic bonds.

A

Structure of glycogen

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2
Q

Glycogen End that contain a terminal glucose w/ a free hydroxyl group at C4

A

Non-reducing end

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3
Q

Glycogen end Has glucose monomer connected to a protein called glycogenin

A

Reducing end

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4
Q

This protein is connected to the reducing end of glycogen:

A

Glycogenin

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5
Q

Glycogenin helps to make a ________, which is crucial for glycogen synthesis.

A

Primer

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6
Q

Enzyme involved in converting glucose to glycogen.

Acts as a primer.

A

Glycogenin

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7
Q

Where is glycogen stored?

A

Liver
And
Muscle

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8
Q

Liver stores 10% by weight and muscle stores 2% by weight, which holds more?

A

Muscle! More SA of muscle than liver

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9
Q

What doesglycogen look like on photomicrogrpah?

A

Granules

Glycogen granules

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10
Q

Glycogen contains what for its own metabolism?

A

Enzymes…more accurate timing

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11
Q

Regulates overall BG levels

Crucial for brain function

A

Liver glycogen

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12
Q

Provides reservoir of fuel [glucose] for physical activity for muscle

A

Muscle glycogen

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13
Q

Regulated storage and release of glycogen

Synthesis and degradation of glycogen involve diff. Pathways

Both pathways regulated independently

A

Glycogen metabolism

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14
Q

3 regulating factors for glycogen metabolism

A

Allosteric control-modulators

Covalent modification-P’s

Hormonal control

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15
Q

Glycogen broken down to release G-1-P-glycogen remnant-remodeled to allow further degradation->

Then, G-1-P converted to G-6-P

A

Glycogenolysis

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16
Q

3 fates of glycogenolysis:

A

glycolysis

Free glucose for release into bloodstream

Pentose phosphate pathway-NADPH and ribose derivative

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17
Q

Catalyzes the cleavage of glycogen- rate limiting step

Chain shortening occurs at the non-reducing end

Adds an orthophosphate and releases a glucose residue as G-1-P

Uses a pyridoxal phosphate (vitB-6) as a cofactor

A

Glycogen phosphorylase (GP)

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18
Q

When does phosphorylation cease?

A

When GP gets w/in 4 Residues of the alpha-1,6 linkage of a branch point

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19
Q

Transfers a block of 3 of the remaining 4 glucose to the non-reducing end of the main chain forming an alpha-1,4 bond

Which enzyme is this involved in glycogenolysis?

A

Transferase

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20
Q

Cleaves the alpha-1,6 bond of the single remaining glucose residue to release free glucose.

Which enzyme is this involved in glycogenolysis?

A

Alpha-1,6 glucosidase

Debranching enzyme

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21
Q

Whic 2 enzymes are responsible for converting branched glycogen into a linear structure for further action by glycogen phosphoylase?

A

Transferase

Alpha-1,6 glucosidase

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22
Q

What enzyme converts G-1-P to G-6-P?

A

Phosphoglucomutase

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23
Q

A phosphorylation group is transferred from the enzyme to the substrate, and a different phosphoryl group is transferred back to restore the enzyme to its initial state

Which enzyme?

A

Phosphoglucomutase

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24
Q

How is G-6-P converted to glucose?

A

It is shipped to the liver b/c it is the only place where you can find g-6-phosphatase

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25
Q

What’re the 2 ways glycogen phosphoryloase is regulated?>

A

Allosteric factors: energy signals of the cell

Reversible phosphorylation (hormones)

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26
Q

Glycogen phosphorylase exists in 2 forms

A

A and B

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27
Q

Liver GP is predominantly which form of GP?

A

Liver is phosphyrlase A and it exists mostly in R relaxed state

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28
Q

Muscle GP is predominantly which form?

A

Phosphorylase B mostly exists in T tense state

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29
Q

Liver and muscle forms of GP are products of seperate genes. What is this called?

A

Isozymes

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30
Q

Form A=

Form B=

A

A=relaxed

B=tense

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31
Q

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

A

Fed-state

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32
Q

Major inactivator of Liver (a) GP?

A

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.

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33
Q

Muscle GP (b) is activated under what conditions?

A

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

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34
Q

AMP GPb activator mechanism:

A

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

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35
Q

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

A

ATP and gluc-6-phosphate

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

36
Q

What role does phosphorylation play in glycogen phosphorylase?

How is it initiated?

A

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

Conversion initiated by hormones

37
Q

Phosphorylation of GP is carried out by what enzyme,?

A

Phosphorylase kinase (PK)

38
Q

How is phosphorylase kinase partially activated?

Fully activated?

A

4 Ca++ ions partially activate PK

4 Ca++ ions and 8 Phosphates fully activates PK

39
Q

What results when Pohsphoylase kinase is fully active?

A

Phosophorylase b converts to phosphorylase a

But requires 2 ATP

40
Q

Wha hormone is released under low [BG] conditions

A

Glucagon

41
Q

Muscle activity releases what hormone?

A

Epinephrine

42
Q

Glucagon and epinephrine are mediated via:

Both of these hormones signal:

A

via G protein coupled receptors (GPCR)

Signal glycogen breakdown

43
Q

Glucagon and epinephrine, can they pass the plasmalemma?

A

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

44
Q

When does glycogen breakdown stop?

A

When the hormone (glucagon or Epi) shuts down

PK and GP are DEphosphorylated =inactivated

When synthesis of glycogen is promoted

45
Q

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

A

Isozymes

46
Q

Liver vs. muscle GP

A

DIFFER: in their sensitivities to regulatory molecules

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

47
Q

Muscle GP is allosterically activated by

A

AMP

48
Q

Liver GP is inactivated by:

Unaffected by:

A

Inactivated by glucose and unaffected by AMP

49
Q

Mutations in liver GP causes

A

Hers disease

50
Q

Mutaiton in muscle GP causes:

A

McArdle syndrome

51
Q

3 key events in glycogenesis:

A
  1. Trapping and activating of glucose.
  2. Elongation of glycogen polymer
  3. Branching of glycogen chains.
52
Q

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

This traps glucose in theses cells.

A

Glucokinase / hexokinase

53
Q

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

A

Phosphoglucomutase

54
Q

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

A

Uridine diphosphate (UDP)-glucose pyrophosphorylase

55
Q

Active form of glucose

A

UDP-glucose

56
Q

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

A

generates energy and drives the RXN forward

57
Q

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?

A

Glycogen synthase

58
Q

Rate limiting rx of glycogenesis

A

Glycogen synthase

59
Q

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

A

Glycogen synthase

60
Q

Glycogenin requires

A

Manganese-Mn

61
Q

whenglycogen reaches 11 residues, a fragment of the chain [about 7 residues long] is broken off at an alpha-1,4 link and reattached elsewhere through an alpha-1,6 link by activity of what enzyme?

A

Glucosyl (4:6) transferase

62
Q

The new branching point must be at least ___ residues away from a preexisting branch

A

4

63
Q

What are the 2 reasons for branching of glycogen?

A
  1. Increases solubility
  2. Increases number of terminal non-reducing ends

Increases rate at which glycogen can be synthesized and degraded

64
Q

Key enzyme in glycogen synthesis

A

Glycogen synthase

65
Q

2 forms of glycogen synthase

A

One form in the liver

One form in the muscles and other tissues

66
Q

Active [non-phosphorylated] form = a form

Inactive [phosphorylated] b form

Interconversion mediated by covalent modifications [fine-tuning role]. What is this regulation?

A

Regulation of glycogen synthesis

67
Q

Glycogen synthesis is regulated by what enzyme that phosphorylates?

A

Glycogen synthase kinase

-GSK

68
Q

What hormones affect GSK?

Allosteric regulation?

A

Insulin and PKA

Allosteric: glucose-6-phosphate [powerful activator]- stabilizes the R state

69
Q

Synthesis and degradation of glycogen pathways are:

A

Independent

Allows for independent regulation.

70
Q

The 2 key enzymes to glycogen metabolism:

A

Glycogen phosphorylase (GP)

Glycogen synthase

Both are the rate limiting steps of degradation/synthesis

Both enzymes are regulated by reversible phosphorylation but effects are in opposite directions

71
Q

How do glucagon and epi control both glycogen breakdown and synthesis?

A

Via PKA!

72
Q

What is the centerpiece intermediate in glycogen metabolism?

A

PKA

73
Q

GP function

A

Stimulate glycogen breakdown

74
Q

Glycogen synthase function:

A

Stimulate glycogen synthesis.

75
Q

What is favored in fed state: glycogenolysis or glycogenesis:

A

Glycogenesis

B/c BG and insulin elevated and cellular ATP is high- signal of high energy

-when glycogen synthesis is favored, the DEPHOSPHO form of glycogen synthase (active) and glycogen phosphorylase(inactive) are predominant

76
Q

What is favored in fasting state: glycogenolysis or glycogenesis:

A

Glycogenolysis

B/c BG levels are low and glucagon levels are high and cellular Ca++ and AMP are elevated -like exercise

-when glycogen degradation is favored PHOSPHORYLATED forms of glycogen synthase (inactive) and glycogen phosphoylase (active) are predominant

77
Q

High BG

Release of _____ by beta cells of pancreas

Binding to its receptor tyrosine kinase

Activation of signaling cascade

A

Regulation by insulin; insulin

78
Q

4 key proteins in Regulation by insulin:

A
  • GLUT 4 [glu transporter]
  • Protein kinase B [PKB]
  • Protein phosphatase 1 [PP1]
  • Glycogen synthase kinase 3 [GSK3]
79
Q

Net result of insulin

A

Activation of glycogen synthase and inactivation of glycogen phosphorylase

80
Q

Formation of insulin receptor complex i activated by:

A

Protein kinase B
[PKB]

This also translocates GLUT to membrane

81
Q

What phosphorylates PP1 (active) and GSK3 (inactive)

A

PKB

82
Q

What is function of PP1

A

Active PP1 dephosphorylates glycogen synthase (activates it)

And

Dephosphorylates glycogen phosphorylase (GP-deactivating it)

83
Q
  • Reduced sensitivity to insulin
  • Called insulin resistance
  • Mutations in insulin receptor and/or downstream signaling proteins

-Down-regulation in receptor levels triggered by elevated insulin [leading 2 endocytosis and degradation of the insulin receptor].notreplaced by translation

What type disorder is this?

A

Type II diabetes

84
Q

What is the glucose sensor in the liver cells?

A

Glycogen phosphorylase

85
Q

Glucose has what effect when bound to liver GP (a)?

A

Deactivates it and allows glycogen synthase to begin storing energy…b/c it is in fed state or high energy

86
Q

McArdle syndrome is a disease of:

A

Muscle GP

Limited ability to perform strenuous exercise b/c of painful muscle cramps; otherwise patient is normal.

87
Q

Hers disease is:

A

Liver GP issue

Milder form of liver enlargement, FTT, hypoglycemia, ketosis, hyperuricemia, hyperlipidemia

Biochemistry (13 decks)

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