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Block 3 Week 2 Meg > Glycogen TBL > Flashcards

Glycogen TBL Flashcards

1
Q

Approximately what percentage of the liver is glycogen? Approximately what percentage of the muscle is glycogen?

A

8%; 1%

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2
Q

So, how is there more glycogen stored in muscle than in the liver?

A

People have more muscle than liver

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3
Q

Describe the structure of glycogen

A

branched polymer of 10-40,000 glucose residues
has 1 reducing end
many nonreducing ends

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4
Q

What portion of the glycogen molecule provides the substrates for glycogen metabolism?

A

the nonreducing ends

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5
Q

List the steps of glycogenesis

A

Glucose –>G6P
G6P –>G1P via phospho-glucomutase
G1P –>UDP-glucose via UDP-glucose pyrophosphorylase
UDP-glucose to UDP + the addition of 1 carbon onto growing glycogen chain via glycogen synthase

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6
Q

What is the driving force that takes Glucose-1-phosphate to UDP glucose?

A

the hydrolysis of pyrophosphate

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7
Q

UDP is attached to glucose at what carbon before being transferred to the C4 hydroxyl group at the nonreducing end of the glycogen chain?

A

C1

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8
Q

transfers 7 unbranched residues to a C6 in a more interior location ≥ 4 residues from a previous alpha1-6 branch point

A

glycogen branching enzyme

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9
Q

What is the price of glycogen synthesis?

A

2 phosphoanhydride bonds/glucose
1 ATP for glucokinase
1 UTP to make UDP-glucose

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10
Q

How is glucose released from glycogen?

A

glycogenolysis

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11
Q

What two enzymes are a part of glycogenolysis?

A
  1. glycogen phosphorylase

2. debranching enzyme

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12
Q

What is the regulated step of glycogenolysis? What occurs during this step?

A

glycogen phosphorylase; cleaving of alpha 1-4 bond

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13
Q

What are two actions of the debranching enzyme?

A
  1. transglycoylase (transfers the branch to the nonreducing end)
  2. glucosidase (cleaves the alpha1-6 bond at the branch point)
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14
Q

Uses inorganic phosphate to cleave glycogen at the non-reducing end to produce Glucose-1-phosphate

A

glycogen phosphorylase

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15
Q

Where does glycogen phosphorylase stop when cleaving the glycogen chain?

A

4 residues before a branch point

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16
Q

Transfers a block of 3 glucose residues to the C4 end of another chain
Cannot cleave the alpha1,6 bond

A

Transglycosylase

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17
Q

Cleaves the alpha1,6 bond releasing 1 glucose

A

Glucosidase

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18
Q

During fasting in the liver, glycogen degradation generates G1P and glucose. G1P is then taken to what product, which is ultimately dephosphorylated to generate glucose that enters the blood?

A

G6P

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19
Q

Where does the conversion of G6P to glucose occur?

A

ER

20
Q

How is the degradation of glycogen different in the muscle than in the liver?

A

In the muscle, there is no glucose-6-phosphatase, so glucose cannot leave the cell to enter the blood

21
Q

In which location, liver or muscle, is glycogen degradation “glucose sparing”?

A

in the muscle (no G-6-Pase)

22
Q

How do hormones regulate glycogen metabolism?

A

phosphorylation

23
Q

What does insulin stimulate?

A

glycogen synthesis

24
Q

What does glucagon stimulate?

A

glycogen degradation

25
Q

What do norepinephrine and epinephrine stimulate in liver and muscle?

A

glycogen degradation

26
Q

What is released from pancreatic Beta cells, leading to reduced cAMP levels, inhibition of glycogen kinase-3, and stimulation of PP1?

A

insulin

27
Q

How does insulin activate glycogen synthase?

A

Insulin reduces cAMP, inhibits GSK3, which prevents phosphorylation of glycogen synthase, rendering it active

28
Q

Insulin stimulates this enzyme which dephosphorylates glycogen synthase

A

PP1

29
Q

What does phosphorylation do to glycogen synthase vs glycogen phosphorylase?

A

inactives glycogen synthase

activates glycogen phosphorylase

30
Q

In what ways does epinephrine differentially regulate metabolism in the liver vs the muscle? (3 ways)

A
  1. different receptors
  2. different enzyme isoforms
  3. different enzyme expression
31
Q

In muscle, what does glycogen get degraded to upon stimulation by epinephrine?

A

pyruvate

32
Q

In the liver, what does glycogen get degraded to upon stimulation by epinephrine?

A

G-6-P to blood glucose

33
Q

Most common glycogen storage disease

A

X-linked phosphorylase kinase deficiency

34
Q

Liver: Disease caused by defective G6Pase

A

von Gierke’s disease

35
Q

Liver: defective glycogen phosphorylase or phosphorylase kinase
Symptoms: hepatomegaly, accumulation of glycogen in the liver

A

Hers’ disease

36
Q

Liver: defective amylo1,6 glycosidase

A

Cori’s disease

37
Q

Muscle: defective glycogen phosphorylase
Symptoms: limited ability to perform strenuous exercise

A

McArdel’s disease

38
Q

Muscle: defective PFK1
Symptoms: poor exercise tolerance, muscle glycogen very high

A

Tarui disease

39
Q

Muscle and nervous system: absence of lysosomal alpha1,4 glucosidase and alpha1,6glucosidase
Symptoms: accumulation of glycogen in lysosomes, cardiorespiratory failure causes death

A

Pompe disease

40
Q

Since G6P cannot leave the cell in skeletal muscle to form glucose, what pathway does it enter instead?

A

glycolysis

41
Q

Once there are 11 residues in a growing glycogen chain, how many residues are removed and attached at a new alpha1,6 branch point?

A

7 residues

42
Q

Does insulin generally reduce or increase phosphorylation of regulated enzymes?

A

reduces phosphorylation

43
Q

What does insulin ultimately stimulate to prevent further breakdown of glycogen?

A

PP1

44
Q

What enzyme phosphorylates glycogen synthase, rendering it inactive?

A

GSK3

45
Q

Is glycogen phosphorylase more or less active when phosphorylated? Is glycogen synthase more or less active when phosphorylated?

A

more; less

Block 3 Week 2 Meg (8 decks)

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