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

Phosphofructokinase-1 catalyzes the committed step of glycolysis. When a cell's ATP concentration is high relative to demand, how is flux through glycolysis affected and why?

A.Flux accelerates because abundant ATP gives PFK-1 more substrate for its forward reaction.
B.Flux stops completely because ATP occupies the active site where fructose 6-phosphate binds.
C.Flux slows because ATP binds an allosteric site on PFK-1 and lowers the enzyme's affinity for fructose 6-phosphate.
D.Flux is unaffected because enzymes that use ATP ignore changes in its concentration.

Explanation

Core Concept

PFK-1 is allosterically inhibited when cellular energy charge is high. ATP attaching at its regulatory site shifts the enzyme toward a lower-affinity state, raising the apparent Km for fructose 6-phosphate without blocking the active site. Slowing the committed step prevents needless glucose breakdown when ATP supply already exceeds demand. As ATP is drained and AMP accumulates, AMP relieves this inhibition and flux recovers.

Correct Answer

CFlux slows because ATP binds an allosteric site on PFK-1 and lowers the enzyme's affinity for fructose 6-phosphate.

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