Question

please answer 1-4

1. The debranching enzyme releases a free glucose molecule by:

a. phosphorylation of the glucose residue.

b. hydrolysis of the α-1,6-glycosidic bond.

c. shifting a phosphoryl group from C-1 to C-6 in the glucose residue.

d. hydrolysis of the α-1,4-glycosidic bond.

e. dephosphorylation of the glucose residue.

2.  One mechanism for turning off glycogen degradation involves the removal of a phosphate group from glycogen phosphorylase by the enzyme _______.

3. How many glucose molecules can one glycogen phosphorylase get from the fragment of glycogen that consists of two branches, each containing 11 α-1,4 linkages and the branching comes from the third glucose unit from the reducing end?

a. 24

b. 13

c. 11

d. 22

e. 12

4. Why is the T state of glycogen phosphorylase less active?

a. ATP cannot be bound by the T state.

b. The adjacent amino acids are not phosphorylated and thus catalysis cannot be carried out.

c. Phosphorylase in the T state has a ridge structure.

d. The adjacent amino acids are phosphorylated and thus the active state is blocked.

e. The active site is partially blocked.

Answer 1

1. b. hydrolysis of the α-1,6-glycosidic bond.

Glycogen phosphorylase enzyme cleaves its substrate by the addition of orthophosphate, whereas Debranching enzyme hydrolyzes the α-1,6-glycosidic bonds that forms branches in glycogen.

2. Protein phosphatase enzyme

Glycogen phosphorylase is deactivated by the removal of a phosphate group (dephosphorylation) from it by the enzyme, protein phosphatase-l or 2A.

3. 24

Each branch containing 11 α-1,4 linkages will have 12 glucose units.

4. e. The active site is partially blocked.

The transition from the T state of Glycogen phosphorylase to the R state involves a 10-degree rotation around the twofold axis of the dimer, which move a loop out of the active site of each subunit. Thus, active site is partly blocked in less active T state. In the active R state, the catalytic site is more accessible and well organized.