Glycogen Metabolism

Question 1

what is glycogenesis?

Answer 1

formation of glycogen

Question 2

what is glycogenolysis?

Answer 2

breakdown of glycogen

Question 3

glycogenesis starts with what molecule?

Answer 3

G6P

Question 4

In glycogenesis, G6P is __1___ in a reversible rxn to __2____

Answer 4

1. isomerized

2. glucose-1-phosphate (G1P)

Question 5

In glycogenesis, G1P is activated with __1__ to form __2__-glucose

Answer 5

1. UTP

2. UDP-glucose

Question 6

In glycogenesis, UDP-glucose is added to the growing glycogen polymer by _____

Answer 6

glycogen synthase

Question 7

glycogenolysis starts with the __1___ and removal of one glucose unit at the end of the glycogen polymer, producing __2___

Answer 7

1. phosphorylation

2. glucose-1-P

Question 8

In glycogenolysis, G1P is __1___ to form __2__

Answer 8

1. isomerized

2. G6P

Question 9

In glycogenolysis, does G6P have to be dephosphorylated into glucose before it reenters the glycolytic pathway?

Answer 9

no. only if the glucose needs to be let into the bloodstream does G6P need to undergo dephosphorylation by glucose-6-phosphatase

Question 10

What enzyme is utilized in glycogenesis to isomerize G6P into G1P?

Answer 10

phosphoglucomutase

Question 11

What enzyme is utilized in glycogenesis to activate G1P into UDP-glucose?

Answer 11

UDP-glucose pyrophosphorylase

Question 12

What enzyme is utilized in glycogenolysis to remove one glucose molecule from glycogen, forming G1P?

Answer 12

glycogen phosphorylase

Question 13

why does skeletal muscle lack glucose-6-phosphatase?

Answer 13

to prevent G6P from being converted into glucose. Muscle cells undergo glycogenolysis to supply muscle cells and muscle cells alone with glucose during exercise. If G6P were turned into glucose, then it would be able to leave the muscle cell. Thus, the muscle cell would lose its energy source. G6P can be immediately used in the glycolytic pathway for energy without leaving the muscle cell.

Question 14

Does insulin stimulate or inhibit glycogenesis? glycogenolysis? Why?

Answer 14

stimulates glycogenesis
inhibits glycogenolysis

It may seem odd that insulin promotes the breakdown of glucose but also the formation of glycogen. This is because your body doesn’t always need to use the food/energy you give it right away at that moment. Some of the food is used as energy, and some of the food is stored for later.

Question 15

Does glucagon stimulate or inhibit glycogenesis? glycogenolysis?

Answer 15

inhibits glycogenesis

stimulates glycogenolysis

Question 16

Patients with Von Gierke’s disease have a deficiency in the enzyme glucose-6-phosphatase. What would you expect these patients’ blood glucagon and insulin levels to be?

Answer 16

Having an absence of G6Pase means that the liver cannot produce free glucose to be released into the bloodstream. Thus, patients will have low levels of blood glucose, leading to chronically high levels of glucagon and low levels of insulin.