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Flashcards in Glycogen TBL Deck (45)
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1

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

8%; 1%

2

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

People have more muscle than liver

3

Describe the structure of glycogen

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

4

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

the nonreducing ends

5

List the steps of glycogenesis

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

6

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

the hydrolysis of pyrophosphate

7

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

C1

8

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

glycogen branching enzyme

9

What is the price of glycogen synthesis?

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

10

How is glucose released from glycogen?

glycogenolysis

11

What two enzymes are a part of glycogenolysis?

1. glycogen phosphorylase
2. debranching enzyme

12

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

glycogen phosphorylase; cleaving of alpha 1-4 bond

13

What are two actions of the debranching enzyme?

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

14

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

glycogen phosphorylase

15

Where does glycogen phosphorylase stop when cleaving the glycogen chain?

4 residues before a branch point

16

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

Transglycosylase

17

Cleaves the alpha1,6 bond releasing 1 glucose

Glucosidase

18

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?

G6P

19

Where does the conversion of G6P to glucose occur?

ER

20

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

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

21

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

in the muscle (no G-6-Pase)

22

How do hormones regulate glycogen metabolism?

phosphorylation

23

What does insulin stimulate?

glycogen synthesis

24

What does glucagon stimulate?

glycogen degradation

25

What do norepinephrine and epinephrine stimulate in liver and muscle?

glycogen degradation

26

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

insulin

27

How does insulin activate glycogen synthase?

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

28

Insulin stimulates this enzyme which dephosphorylates glycogen synthase

PP1

29

What does phosphorylation do to glycogen synthase vs glycogen phosphorylase?

inactives glycogen synthase
activates glycogen phosphorylase

30

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

1. different receptors
2. different enzyme isoforms
3. different enzyme expression

31

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

pyruvate

32

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

G-6-P to blood glucose

33

Most common glycogen storage disease

X-linked phosphorylase kinase deficiency

34

Liver: Disease caused by defective G6Pase

von Gierke's disease

35

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

Hers' disease

36

Liver: defective amylo1,6 glycosidase

Cori's disease

37

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

McArdel's disease

38

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

Tarui disease

39

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

Pompe disease

40

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

glycolysis

41

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

7 residues

42

Does insulin generally reduce or increase phosphorylation of regulated enzymes?

reduces phosphorylation

43

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

PP1

44

What enzyme phosphorylates glycogen synthase, rendering it inactive?

GSK3

45

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

more; less