MCAT Biochemistry Question 139: Answer and Explanation

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Question: 139

4. Which of the following processes has the following net reaction?

2 acetyl-CoA + 6 NAD⁺ + 2 FAD + 2 GDP + 2 P_i + 6 H₂O → 4 CO₂ + 6 NADH + 2 FADH₂ + 2 GTP + 6 H⁺ + 2 CoA–SH

A. Glycolysis
B. Fermentation
C. Tricarboxylic acid cycle
D. Electron transport chain

Correct Answer: C

Explanation:

It is not necessary to have all the net reactions memorized for each metabolic process to answer this question; all we need is to identify a few key reactants and products. In this case, we start with acetyl-CoA and end with CoA–SH. We also notice that in this reaction, NAD⁺ and FAD are reduced to NADH and FADH₂, and that CO₂ is formed. The only metabolic process in which all of the above reactions would occur is the citric acid cycle, also called the tricarboxylic acid (TCA) or Krebs cycle.

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