Following statements are made regarding glycogen phosphorylase and glycogen synthase activities in relation to their phosphorylation status:

A. Phosphorylation of glycogen phosphorylase increases its activity
B. Phosphorylation of glycogen phosphorylase decreases its activity
C. Phosphorylation of glycogen synthase increases its activity
D. Phosphorylation of glycogen synthase decreases its activity

Which one of the following is a combination of correct statements?

Correct option is D

Explanation -

There are  two key enzymes that regulate glycogen metabolism:
Glycogen Phosphorylase
Function: Breaks down glycogen into glucose-1-phosphate
Pathway: Glycogenolysis
Glycogen Synthase
Function: Synthesizes glycogen from glucose
Pathway: Glycogenesis
These enzymes are regulated by phosphorylation — a common way cells turn enzymes "on" or "off" using kinase or phosphatase enzymes.

Effect of Phosphorylation:
1. Glycogen Phosphorylase
            Phosphorylation = ACTIVATION
            When glycogen phosphorylase is phosphorylated, it becomes active (called glycogen phosphorylase a).
            Promotes glycogen breakdown → raises blood glucose.
            Triggered by glucagon or epinephrine (when glucose is needed).
Statement A is correct - ​ Phosphorylation of glycogen phosphorylase increases its activity.
Statement B is incorrect - ​ Phosphorylation of glycogen phosphorylase decreases its activity.

2. Glycogen Synthase
             Phosphorylation = INACTIVATION
             When glycogen synthase is phosphorylated, it becomes inactive (called glycogen synthase b).
             This prevents glycogen formation (you don’t want to store glucose when you're trying to release it).
Statement D is correct - ​ Phosphorylation of glycogen synthase decreases its activity.
Statement C is incorrect - ​ Phosphorylation of glycogen synthase increases its activity.

So, the correct answer is option d - A and D.