Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologymediummcq1 pt

Cleavage of fructose-1,6-bisphosphate yields one glyceraldehyde-3-phosphate (G3P) and one dihydroxyacetone phosphate (DHAP), yet the payoff phase still processes two G3P molecules per glucose. Why?

A.DHAP is recycled backward into fructose-1,6-bisphosphate, effectively repeating the investment phase
B.Triose phosphate isomerase rapidly converts DHAP into G3P, so both three carbon fragments flow through the payoff reactions
C.Glycolysis restarts halfway through, generating a second G3P from stored reserves
D.Each G3P passes through the payoff phase twice, doubling the recorded yield

Explanation

Core Concept

DHAP and G3P are structural isomers of the same three carbon sugar phosphate. Triose phosphate isomerase interconverts them within milliseconds, feeding DHAP into the G3P pool just as fast as glyceraldehyde-3-phosphate dehydrogenase drains it. Because consumption pulls the equilibrium along, both fragments ultimately continue. Every glucose therefore delivers two trioses to the payoff phase, doubling the NADH and ATP yields relative to processing a lone G3P.

Correct Answer

BTriose phosphate isomerase rapidly converts DHAP into G3P, so both three carbon fragments flow through the payoff reactions

More Unit 3: Cellular Energetics practice questions

Try a random question →

Practice more AP Biology questions with full explanations

Practice Unit 3: Cellular Energetics Questions →