Chapter 25 - Glycogen Synthesis

Question 1

Which of the following is a substrate for glycogen synthase?

a. UTP-glucose

b. Glucose 1-phosphate

c. CDP-glucose

d. UDP-glucose

Answer 1

UDP-glucose

Question 2

What reactants are required for UDP-glucose synthesis?

a. Glucose 6-phosphate and UTP

b. Glucose 6-phosphate and UDP

c. Glucose 1-phosphate and UTP

d. Glucose 1-phosphate and UDP

Answer 2

Glucose 1-phosphate and UTP

Question 3

Which enzyme synthesizes UDP-glucose?

Answer 3

UDP-glucose phosphorylase

Question 4

What enzymes are required for the synthesis of a glycogen particle starting from glucose 6-phosphate?

Answer 4

Phosphoglucomutase,
UDP-glucose pyrophosphorylase, pyrophospatase,
glycogenin,
glycogen synthase,
branching enzyme

Question 5

Why does activation of the phosphorylated b form of glycogen synthase by high concentrations of glucose 6-phosphate make good biochemical sense?

Answer 5

The presence of high concentrations of glucose 6-phosphate indicates that glucose is abundant and that it is not being used by glycolysis. Therefore this valuable resource is saved by incorporation into glycogen.

Question 6

Describe the role of glycogenin and glycogen synthase in glycogen synthesis

Answer 6

Glycogenin, a dimer, catalyzes the addition of 10 to 20 glucosyl units linked by a alpha-1,4 bonds to each glycogenin subunit. The modified glycogenin then serves as a primer for glycogen synthase, which extends the glycogen chain with the formation of more alpha-1,4 linkages.

Question 7

How does insulin stimulate glycogen synthesis?

Answer 7

insulin binds to its receptor and activates the tyrosine kinase activity of the receptor, which in turn triggers a pathway that activates protein kinases. The signal-transduction pathway results in an increase in the number of glucose transporters to the membrane.