Question

The enzyme glycogen phosphorylase is responsible for regulation of glycogen degradation and can be regulated at 2 levels: ________ and _________

a) Allosteric regulation; protein phosphorylation
b) Allosteric regulation; glycosylation
c) Competitive inhibition; protein phosphorylation
d) Glycosylation; protein phosphorylation
e) Competitive inhibition, allosteric regulation

Answer 1

a) Allosteric regulation; protein phosphorylation

Step-by-step explanation:

Glycogen phosphorylase is an enzyme which is responsible for regulation of glycogen degradation and it is regulated at two levels:

(1) Allosteric regulation

(2) Protein phosphorylation

Glycogen phosphorylase exists in two forms which are inter-convertible. The two forms are 'glycogen phosphorylase a' & 'glycogen phosphorylase b'.

Glycogen phosphorylase b is less active form while glycogen phosphorylase a is more active form. When phosphorylation occurs at hydroxyl group of the serine residue of glycogen phosphorylase b then it gets converted into glycogen phosphorylase a. Once it gets activated, it leads to the degradation of glycogen. Here it may be noted that the phosphorylation occurs only when blood glucose level is low so glycogen needs to be degraded to regenerate glucose and send it back to the blood so that blood sugar level could become normal.

As soon as the level of glucose in our blood gets normal there is no need of glycogen breakdown. So the glucose enters in the hepatocytes and binds to an inhibitory allosteric site on enzyme 'glycogen phosphorylase a' as a result of which the enzyme becomes inactive and no more glycogen is degraded.