Week 13 P2

Question 1

What is glycogen?

Answer 1

A branched polymer of glucose used for storage of glucose in liver and muscle.

Question 2

What type of bonds are in glycogen?

Answer 2

α-1,4 glycosidic bonds (linear) and α-1,6 glycosidic bonds (branches).

Question 3

What is the function of branching in glycogen?

Answer 3

Increases solubility and allows rapid synthesis and degradation.

Question 4

What protein forms the core of glycogen?

Answer 4

Glycogenin.

Question 5

What is glycogenesis?

Answer 5

The synthesis of glycogen from glucose.

Question 6

First step of glycogenesis?

Answer 6

Glucose → glucose-6-phosphate (hexokinase in muscle, glucokinase in liver).

Question 7

Which enzyme converts G6P to G1P?

Answer 7

Phosphoglucomutase.

Question 8

What is the activated form of glucose?

Answer 8

UDP-glucose.

Question 9

Enzyme that elongates glycogen chains?

Answer 9

Glycogen synthase.

Question 10

Which enzyme creates branches?

Answer 10

Branching enzyme (α-1,4 → α-1,6 transferase).

Question 11

Minimum chain length before branching occurs?

Answer 11

About 8 glucose residues.

Question 12

What is glycogenolysis?

Answer 12

Breakdown of glycogen to glucose-1-phosphate and free glucose.

Question 13

Rate-limiting enzyme of glycogenolysis?

Answer 13

Glycogen phosphorylase.

Question 14

What bond does glycogen phosphorylase cleave?

Answer 14

α-1,4 glycosidic bonds.

Question 15

Cofactor of glycogen phosphorylase?

Answer 15

Pyridoxal phosphate (vitamin B6).

Question 16

What enzyme removes branches?

Answer 16

Debranching enzyme.

Question 17

Two activities of debranching enzyme?

Answer 17

• Transferase (moves trisaccharide) • α-1,6-glucosidase (releases free glucose)

Question 18

Is glycogenolysis the reverse of glycogenesis?

Answer 18

No, they use different enzymes.

Question 19

Why must the two pathways be reciprocally regulated?

Answer 19

To prevent futile cycling and energy waste.

Question 20

Effect of phosphorylation on glycogen synthase?

Answer 20

Inactivates it.

Question 21

Effect of phosphorylation on glycogen phosphorylase?

Answer 21

Activates it.

Question 22

Main function of liver glycogen?

Answer 22

Maintain blood glucose.

Question 23

Main function of muscle glycogen?

Answer 23

Provide glucose for muscle contraction.

Question 24

Why can’t muscle release free glucose into blood?

Answer 24

Muscle lacks glucose-6-phosphatase.

Question 25

Which hormone stimulates glycogenolysis in liver?

Answer 25

Glucagon.

Question 26

Which hormone stimulates glycogenolysis in muscle?

Answer 26

Epinephrine.

Question 27

Which hormone stimulates glycogenesis?

Answer 27

Insulin.

Question 28

Does muscle respond to glucagon?

Answer 28

No.

Question 29

Second messenger used by glucagon and epinephrine?

Answer 29

cAMP.

Question 30

What activates muscle glycogen phosphorylase allosterically?

Answer 30

AMP.

Question 31

What activates phosphorylase kinase?

Answer 31

Ca²⁺ (during muscle contraction).

Question 32

Enzyme deficiency in Von Gierke disease?

Answer 32

Glucose-6-phosphatase.

Question 33

Main organ affected in Von Gierke disease?

Answer 33

Liver.

Question 34

Major biochemical problem in Von Gierke disease?

Answer 34

Cannot release free glucose from liver.

Question 35

Main symptoms of Von Gierke disease?

Answer 35

• Severe fasting hypoglycemia • Hepatomegaly • Lactic acidosis • Hyperuricemia • Hyperlipidemia

Question 36

Why is glycogen increased in Von Gierke disease?

Answer 36

G6P is trapped and converted back to glycogen.

Question 37

Enzyme deficiency in McArdle disease?

Answer 37

Muscle glycogen phosphorylase.

Question 38

Main tissue affected in McArdle disease?

Answer 38

Muscle.

Question 39

Main symptoms of McArdle disease?

Answer 39

• Exercise intolerance • Muscle cramps • Myoglobinuria • No rise in blood lactate after exercise

Question 40

Why is blood glucose normal in McArdle disease?

Answer 40

Liver glycogen metabolism is normal.

Question 41

How does insulin affect glycogen metabolism?

Answer 41

Activates glycogen synthase and inhibits glycogen phosphorylase.

Question 42

How does glucagon affect glycogen metabolism?

Answer 42

Activates glycogen phosphorylase and inhibits glycogen synthase.

Question 43

Why does Von Gierke cause hypoglycemia but McArdle does not?

Answer 43

Von Gierke affects liver glucose release; McArdle affects muscle only.

Question 44

Why does McArdle cause exercise intolerance?

Answer 44

Muscle cannot mobilize its glycogen for ATP.

Question 45

What happens to liver glycogen after 12–18 hours of fasting?

Answer 45

It becomes almost completely depleted.