Q8. Which of the following enzymes are active in the dephosphorylated state?  1. Glycogen synthase  2. Glycogen phosphorylase  3. Fructose-2,6-bisphosphatase  4. Phosphofructokinase-2 (PFK-2)

1. A

   A. 1 and 2

2. B

   B. 2 and 3

3. C

   C. 3 and 4

4. D

   D. 1 and 4

Appeared in: INI-CET EXAM -2026

Explanation

• Dephosphorylation is primarily driven by insulin signaling, which occurs in the well-fed state.
• In the fed state, the body aims to store and utilize glucose.
• Glycogen synthase is the key enzyme for storing glucose as glycogen. It is activated by dephosphorylation, promoting glycogenesis.
• Phosphofructokinase-2 (PFK-2) is the kinase domain of a bifunctional enzyme. Its dephosphorylation (activation) leads to the production of fructose-2,6-bisphosphate, a powerful activator of glycolysis, thus promoting glucose utilization.

Why Other Options Were Wrong

• Option A: This option incorrectly includes Glycogen phosphorylase (2). Glycogen phosphorylase is active in its phosphorylated state, which promotes glycogen breakdown.
• Option B: This option is incorrect because both Glycogen phosphorylase (2) and Fructose-2,6-bisphosphatase (3) are active in their phosphorylated states, not dephosphorylated.
• Option C: This option incorrectly includes Fructose-2,6-bisphosphatase (3). This enzyme domain is active in its phosphorylated state, where it breaks down an activator of glycolysis.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Regulation of metabolic enzymes by phosphorylation and dephosphorylation as background academic context rather than a clinical decision trigger.
• Understanding this regulation is fundamental to comprehending blood glucose homeostasis.
• Hormones like insulin (promotes dephosphorylation) and glucagon (promotes phosphorylation) are key regulators. Insulin deficiency or resistance, as seen in diabetes mellitus, disrupts this balance, leading to hyperglycemia.
• Nursing care for diabetic patients involves administering insulin, which helps activate enzymes like glycogen synthase and PFK-2 to lower blood glucose by promoting its storage and utilization.

How to Approach the Question

• First, identify the core concept: regulation of enzyme activity by phosphorylation/dephosphorylation (covalent modification).
• Recall the general rule: dephosphorylation is often associated with the 'fed state' and insulin signaling, while phosphorylation is associated with the 'fasting state' and glucagon signaling.
• Consider each enzyme's function. In a fed state (dephosphorylated), the body wants to store glucose (glycogen synthesis) and use it (glycolysis).
• Analyze the enzymes: Glycogen synthase (1) makes glycogen, so it should be active. PFK-2 (4) promotes glycolysis, so it should be active.
• Conversely, Glycogen phosphorylase (2) breaks down glycogen, and Fructose-2,6-bisphosphatase (3) inhibits glycolysis; these should be inactive in the fed state.
• Combine the active enzymes (1 and 4) to find the correct option.

Concept Tested & Keywords

• Concept Tested: Regulation of metabolic enzymes by phosphorylation and dephosphorylation.
• Stem keywords: enzymes, active, dephosphorylated state, Glycogen synthase, Glycogen phosphorylase, Fructose-2,6-bisphosphatase, Phosphofructokinase-2
• Lead-in keywords: Which of the following

Question ID

Q3xttxfq5CpSg8ZaomYUzA

Copy ID

Reference Book

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) pp. 168-170, 77-79

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 161-163