Glycogen TBL

Question 1

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

Answer 1

8%; 1%

Question 2

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

Answer 2

People have more muscle than liver

Question 3

Describe the structure of glycogen

Answer 3

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

Question 4

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

Answer 4

the nonreducing ends

Question 5

List the steps of glycogenesis

Answer 5

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

Question 6

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

Answer 6

the hydrolysis of pyrophosphate

Question 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?

Answer 7

C1

Question 8

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

Answer 8

glycogen branching enzyme

Question 9

What is the price of glycogen synthesis?

Answer 9

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

Question 10

How is glucose released from glycogen?

Answer 10

glycogenolysis

Question 11

What two enzymes are a part of glycogenolysis?

Answer 11

1. glycogen phosphorylase

2. debranching enzyme

Question 12

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

Answer 12

glycogen phosphorylase; cleaving of alpha 1-4 bond

Question 13

What are two actions of the debranching enzyme?

Answer 13

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

Question 14

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

Answer 14

glycogen phosphorylase

Question 15

Where does glycogen phosphorylase stop when cleaving the glycogen chain?

Answer 15

4 residues before a branch point

Question 16

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

Answer 16

Transglycosylase

Question 17

Cleaves the alpha1,6 bond releasing 1 glucose

Answer 17

Glucosidase

Question 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?

Answer 18

G6P

Question 19

Where does the conversion of G6P to glucose occur?

Answer 19

ER

Question 20

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

Answer 20

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

Question 21

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

Answer 21

in the muscle (no G-6-Pase)

Question 22

How do hormones regulate glycogen metabolism?

Answer 22

phosphorylation

Question 23

What does insulin stimulate?

Answer 23

glycogen synthesis

Question 24

What does glucagon stimulate?

Answer 24

glycogen degradation

Question 25

What do norepinephrine and epinephrine stimulate in liver and muscle?

Answer 25

glycogen degradation

Question 26

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

Answer 26

insulin

Question 27

How does insulin activate glycogen synthase?

Answer 27

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

Question 28

Insulin stimulates this enzyme which dephosphorylates glycogen synthase

Answer 28

PP1

Question 29

What does phosphorylation do to glycogen synthase vs glycogen phosphorylase?

Answer 29

inactives glycogen synthase | activates glycogen phosphorylase

Question 30

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

Answer 30

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

Question 31

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

Answer 31

pyruvate

Question 32

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

Answer 32

G-6-P to blood glucose

Question 33

Most common glycogen storage disease

Answer 33

X-linked phosphorylase kinase deficiency

Question 34

Liver: Disease caused by defective G6Pase

Answer 34

von Gierke's disease

Question 35

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

Answer 35

Hers' disease

Question 36

Liver: defective amylo1,6 glycosidase

Answer 36

Cori's disease

Question 37

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

Answer 37

McArdel's disease

Question 38

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

Answer 38

Tarui disease

Question 39

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

Answer 39

Pompe disease

Question 40

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

Answer 40

glycolysis

Question 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?

Answer 41

7 residues

Question 42

Does insulin generally reduce or increase phosphorylation of regulated enzymes?

Answer 42

reduces phosphorylation

Question 43

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

Answer 43

PP1

Question 44

What enzyme phosphorylates glycogen synthase, rendering it inactive?

Answer 44

GSK3

Question 45

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

Answer 45

more; less