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601 - Exam 1 > 2.9 Glycogen Metabolism > Flashcards

2.9 Glycogen Metabolism Flashcards

1
Q

Define glycogen

A

A soluble polymer of many glucose units

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2
Q

Define glycogenesis

A

Intracellular synthesis of glycogen from glucose

- Occurs in cytosol of liver and muscle cells

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3
Q

Define Glycogenolysis

A

Intracellular breakdown of glycogen to form glucose

- Breakdown of glycogen

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4
Q

Describe liver glycogen

A
  • Short term energy
  • Liver stores and releases glucose from glycogenolysis in response to low blood glucose levels
  • Puts glucose back in blood when brain needs it
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5
Q

Describe muscle glycogen

A
  • Main fuel substrate during high intensity exercise within muscle cells
  • Depleted after prolonged exercise
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6
Q

Why store glucose as glycogen?

A

A large amount of glucose can’t be in cells b/c accumulation of charged G-6-P has strong osmotic effect (cells swell)

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7
Q

Is glycogen charged or uncharged?

A

Not charged

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8
Q

A non-branched structure doesn’t allow for

A

Rapid synthesis and breakdown

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9
Q

Glycogen core complexes consist of

A

Glycogenin protein

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10
Q

Glycogen synthesis involves

A

Elongation of linear chains and formation of branch points

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11
Q

Glycogen degradation involves

A

Sequential removal of glucose and the disassembly of branch points

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12
Q

What are the enzymes of glycogenesis?

A

Glucokinase
Phosphoglucomutase
UDPG pyrophosphorylase
Glycogen synthase

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13
Q

Glycogenesis is stimulated by

A

Insulin in the liver and muscle

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14
Q

Enzymes involved in glycogenolysis

A

Phosphorylase
Phosphoglucomatuse
Glucose-6-phosphatase

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15
Q

Glycogenolysis is stimulated by

A

Glucagon in the liver and epinephrine in muscle

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16
Q

Most glycogen synthesis occurs via addition of glucose residues to a

A

preexisting glycogen molecule

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17
Q

In the absence of a preexisting glycogen molecule, the protein ___ serves as a ___

A

glycogenin

primer

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18
Q

Describe phosphoglucomutase (PGM)

A

Catalyzes G-1-P and G-6-P

  • It’s required for both synthesis and degradation of glycogen
  • Moves phosphate from position 6 to 1
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19
Q

The first committed step in glycogen synthesis is the formation of

A

Uridine diphosphate (UDP) glucose

20
Q

Hydrolysis of PPi (when UDP glucose is the enzyme) drives glycogen synthesis and prevents a ___

A

Potential futile cycle

- Not reversible

21
Q

Describe glycogen synthase rxn

A

Glycogen chains are elongated 1 UDP-glucose unit at a time via glycogen synthase

22
Q

What bond is formed between UDP-glucose and a glycogen end

A

alpha-1,4-glycosidic bond

23
Q

What transfers 7 glucose units from the end of the chain to an internal position using a alpha-1,6-branch point?

A

glycogen branching enzyme (1,4-alpha-glucagon-branching enzyme)

  • Does this once it reaches 11 glucose residues
24
Q

What is the first step in glycogenolysis?

A

Glycogen phosphorylase catalyzes glycogen to glucose-1-phosphate + glycogen

25
Q

Glycogen phosphorylase breaks the ___ bond, but NOT the ___

A

Breaks = 1,4 bond

DOESN’T break = 1,6 bond

26
Q

What does glycogen transferase do?

A

Removes 3 glucose units by breaking a 1,4 bond on one strand and forming a new 1,4 bond on another

27
Q

What enzyme breaks the 1,6 bond?

A

Debranching enzyme (alpha 1,6-glucosidase)

28
Q

Does the debranching enzyme remove a glucose or glucose-1-phosphate unit?

A

Glucose

29
Q

Complete degradation of glycogen releases ___% of glucose-1-phosphate and ___% glucose moleucles

A

90%

10%

30
Q

What is the second enzyme used in glycogenolysis and what does it do?

A

Phosphoglucomutase

G-1-P to G-6-P

31
Q

What is the third enzyme involved in glycogenolysis and what does it do?

A

Glucose-6-phosphatase

G-6-P to glucose

32
Q

Where is glucose-6-phosphatase located and why?

A

Integral membrane protein of the ER because it separates reaction from glycolysis

33
Q

What’s the process for dephosphorylation of G6P to glucose?

A
  1. G-6-P is transported to ER lumen by a specific transporter (T1)
  2. G-6-P is hydrolyzed by glucose-6-phosphatase
  3. Glucose is transported to cytosol via transporter T2 and out of cell via GLUT2
34
Q

What activates glycogen phosphorylase in muscles?

A

Calcium

35
Q

What happens to glycogen phosphorylase in the liver?

A

It’s inhibited

36
Q

Glycogen synthase and glycogen phosphorylase respond in opposite ways to phosphorylation, GS is ___ and GP is ___

A 
GS = inactivated
GP = activated
37
Q

Muscles don’t respond to glucagon, so what triggers the same pathway?

A

epinephrine

38
Q

When going from G-1-P to glycogen, what enzymes are added to glycogen synthase?

A

Protein kinase A tries to add P from cAMP, but it negatively regulates it
SO
Protein phosphatase from insulin removes a P

39
Q

When going from glycogen to G-1-P, what enzymes are involved with P?

A

Protein phosphatase from insulin removes P
SO
Phosphorylase kinase from glucagon in liver, and epinephrine in muscle adds a P and activates GP to breakdown glycogen

40
Q

Fasting does what

A

Phosphorylates

41
Q

Insulin ___, leading to the activation of pyruvate kinase, pyruvate dehydrogenase and glycogen synthase

A

Dephosphorylates

42
Q

Glucagon leads to phosphorylation of what enzymes? Are they active or inactive?

A 
Pyruvate Kinase (glycolysis) = INACTIVE
Pyruvate dehydrogenase (Pyruvate to Acetyl Co-A) = INACTIVE
Glycogen Synthase (glycogen synthesis) = INACTIVE
Glycogen phosphorylase (glycogen breakdown) = ACTIVATION
43
Q

Insulin is required for storing ___

A

Glucose as glycogen

44
Q

Glucagon is required for releasing ___

A

Glucose from its stores in the liver

45
Q

What is glycogen storage disease (GSD)?

A

Defect in any one of the several enzymes required for either glycogen synthesis or degradation

46
Q

What 2 ways can GSDs be divided into?

A
  • Hepatic involvement (hypoglycemia)

- Those with neuromuscular disease and weakness

601 - Exam 1 (10 decks)

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