Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyhardmcq1 pt

Phosphofructokinase-1 (PFK-1) consumes ATP as a substrate, yet high cellular ATP concentrations slow the very step this enzyme catalyzes. How can one molecule both fuel and restrain glycolysis?

A.ATP alternates between fueling and restraining roles depending on whether the cell is dividing
B.Excess ATP raises the activation energy of PFK-1 beyond what fructose-6-phosphate can overcome
C.PFK-1 mutates rapidly under energy surplus, switching its substrate preference away from ATP
D.ATP binds a second, lower affinity regulatory site that stabilizes the low activity conformation, and rising AMP competes there to relieve the braking

Explanation

Core Concept

At ordinary concentrations ATP occupies only the active site and drives the committed phosphorylation of fructose-6-phosphate. When ATP accumulates, it additionally engages an allosteric pocket devoted solely to control, shifting PFK-1 into its sluggish shape and cutting flux. Rising AMP, the signal of energy scarcity, displaces ATP from that pocket and restores activity. One ligand therefore produces opposite effects by occupying two distinct sites with different affinities.

Correct Answer

DATP binds a second, lower affinity regulatory site that stabilizes the low activity conformation, and rising AMP competes there to relieve the braking

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