Question

Metabolic control analysis does not suggest that ___________

(a) When the blood glucose level rises, insulin acts in muscle to increase glucose transport into cells by bringing GLUT4 to the plasma membrane

(b) When the blood glucose level rises, insulin acts in muscle to induce the synthesis of PFK-1

(c) When the blood glucose level rises, insulin acts in muscle to activate glycogen synthase by covalent alteration

(d) When the blood glucose level rises, insulin acts in muscle to induce the synthesis of hexokinase

I got this question by my college director while I was bunking the class.

This interesting question is from Analysis of Metabolic Control in section Principles of Metabolic Regulation: Glucose and Glycogen of Biochemistry

Answer 1

The correct answer is:

(b) When the blood glucose level rises, insulin acts in muscle to induce the synthesis of PFK-1

Explanation: Metabolic control analysis focuses on how various enzymes and regulatory pathways interact to control metabolic processes.

• (a) is correct because insulin promotes glucose uptake into muscle cells by translocating GLUT4 transporters to the plasma membrane.
• (c) is correct because insulin activates glycogen synthase in muscle through covalent modification (dephosphorylation).
• (d) is correct because insulin increases the synthesis of hexokinase in muscle to facilitate glucose phosphorylation and utilization.

However, (b) is incorrect because PFK-1 (phosphofructokinase-1) is primarily regulated by allosteric effectors (such as ATP, AMP, and fructose-2,6-bisphosphate), not by insulin-induced synthesis. PFK-1 activity is modulated by these factors, but insulin does not directly induce its synthesis in muscle cells.