AAMC FL Practice Exam

What is the main product of the Krebs cycle from one acetyl-CoA molecule?

1. 1 NADH

2. 3 NADH

3. 1 FADH2

4. 2 ATP

The correct answer is: 3 NADH

The main product of the Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, from one acetyl-CoA molecule is indeed the production of three NADH molecules. During each turn of the Krebs cycle, one acetyl-CoA is oxidized, leading to a series of reactions that ultimately result in the reduction of NAD+ to NADH at three different steps in the cycle. These steps involve the conversion of isocitrate to alpha-ketoglutarate, the conversion of alpha-ketoglutarate to succinyl-CoA, and the conversion of malate to oxaloacetate. Each of these reactions is facilitated by specific enzymes and generates one molecule of NADH. In addition to the production of NADH, the cycle also produces one molecule of FADH2 and one molecule of GTP (which can be converted to ATP), but the primary focus in this case is the generation of NADH. Therefore, the generation of three NADH molecules marks a significant output of energy in the form of electron carriers, which are then utilized in subsequent processes such as oxidative phosphorylation to ultimately produce ATP.