Which of the following is not a role played by NADH in cellular respiration?
A It transfers electrons.
B It is involved in redox reactions.
C It oxidizes pyruvate.
D It accepts electrons and hydrogen ions.
E It powers proton pumps.
The correct answer and explanation is:
The correct answer is C: It oxidizes pyruvate.
NADH plays several crucial roles in cellular respiration, but oxidizing pyruvate is not one of them. Here is an explanation of each role and how it relates to NADH:
A. It transfers electrons – NADH is a carrier of electrons. In the process of cellular respiration, NADH is produced during glycolysis, the citric acid cycle, and other metabolic processes. NADH donates electrons to the electron transport chain (ETC), where the electrons move through protein complexes to generate energy for the cell.
B. It is involved in redox reactions – NADH participates in redox (reduction-oxidation) reactions. During glycolysis and the citric acid cycle, NAD+ is reduced to NADH as it accepts electrons from other molecules. This is an essential step in generating energy for the cell.
C. It oxidizes pyruvate – This statement is incorrect. NADH does not oxidize pyruvate. Instead, pyruvate is converted into acetyl-CoA before entering the citric acid cycle, where it undergoes oxidation. The process of oxidation of pyruvate is actually facilitated by enzymes, such as pyruvate dehydrogenase, which produce NADH in the process.
D. It accepts electrons and hydrogen ions – NAD+ accepts electrons and hydrogen ions to form NADH. This is part of the reduction reaction in the metabolic pathways like glycolysis and the citric acid cycle. The reduction of NAD+ to NADH is essential for energy production.
E. It powers proton pumps – NADH plays a role in powering proton pumps within the electron transport chain. As NADH donates its electrons, energy is released to pump protons (H+) across the mitochondrial membrane, creating a proton gradient that drives ATP production.
In summary, NADH is involved in electron transfer, redox reactions, electron acceptance, and proton pumping but does not directly oxidize pyruvate.