Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyeasymcq1 pt

What happens during pyruvate oxidation just before the Krebs cycle begins?

A.Two FADH2 molecules are generated from every pyruvate processed
B.Each pyruvate loses a carboxyl group as CO2 while NAD+ is reduced to NADH, leaving acetyl-CoA
C.ATP is invested to activate pyruvate before cleavage
D.Pyruvate is reduced to lactate within the matrix

Explanation

Core Concept

The pyruvate dehydrogenase complex sits in the mitochondrial matrix and processes each three-carbon pyruvate in three linked steps. First a carboxyl group departs as carbon dioxide, then the remaining two-carbon fragment is oxidized while NAD+ captures the electrons. Finally coenzyme A bonds to the fragment as acetyl-CoA. No ATP appears here, but the NADH and acetyl-CoA feed later energy-yielding stages.

Correct Answer

BEach pyruvate loses a carboxyl group as CO2 while NAD+ is reduced to NADH, leaving acetyl-CoA

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