Glycogen synthase and glycogen phosphorylase are reciprocally regulated by phosphorylation. Which statement correctly describes this regulation?

• A Phosphorylation inactivates glycogen synthase and activates glycogen phosphorylase ✓
• B Phosphorylation activates both glycogen synthase and glycogen phosphorylase
• C Phosphorylation activates glycogen synthase and inactivates glycogen phosphorylase
• D Phosphorylation inactivates both glycogen synthase and glycogen phosphorylase

Explanation

Phosphorylation (by PKA and phosphorylase kinase) inactivates glycogen synthase (reducing glycogen synthesis) while activating glycogen phosphorylase (increasing glycogenolysis). This ensures simultaneous promotion of glycogen breakdown and inhibition of synthesis during fasting/stress. Options B, C, and D contradict this reciprocal logic.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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