Glycogen Synthesis

Question 1

What happens when insulin bonds to the insulin receptor?

Answer 1

Induces a signal transduction cascade which allows the glucose transporter too transport glucose into the cell

Question 2

Outline some effects of insulin;

Answer 2

• activated enzymes that convert glucose to glucagon in liver and muscle cells
• increases conversion of glucose to fat
• glucose<—> glucose phosphate <—> glycogen

Question 3

What are the branches in the glycosidic bonds created by?

Answer 3

1,6-glycosidic bonds

Question 4

What is glucose stored as and where?

Answer 4

Stored as glycogen predominantly in liver and muscle cells

Question 5

What is the immediate precursor for glycogen synthesis?

Answer 5

Uridine disphosphate glucose (UDP-glucose)

Question 6

What is UDP-glucose a form of? And where is it synthesised from?

Answer 6

Activated form of glucose

Synthesised by glucose-1-phosphate and uridine triphosphate (UTP)

Question 7

What is glycogenin?

Answer 7

An enzyme that catalyses attachment of a glucose molecule to one of its own tyrosine residues

Question 8

What is glycogenin?

Answer 8

A dimer

Two copies of the enzyme glucosylate one another

Question 9

What is glycogen synthase?

Answer 9

This enzyme catalyses transfer of glucose molecules from UDP-glucose to a growing chain of glycogen

Question 10

What is amylo-(1,4-1,6) transglycosylase?

Answer 10

Branching enzyme

Cleaves the linear part of the glycogen to give 6 or 7 units of glucose

Question 11

Where is the branching point of amylo-(1,4-1,6) transglycosylase? And what does branching do?

Answer 11

Branch point must be four residues away from a pre-existing one

Branching increases the rate of glycogen synthesis/degradation