Medical College Admission Test (MCAT) Practice Exam 2026 - Free MCAT Practice Questions and Study Guide

In each round of beta-oxidation, fatty acids are broken down into two-carbon units in the form of acetyl-CoA, and for each cycle, one molecule of NADH is generated. The beta-oxidation process consists of a series of four enzymatic reactions: oxidation, hydration, a second oxidation, and thiolysis.

During the first oxidation step, a molecule of NAD+ is reduced to NADH as the fatty acyl-CoA is converted to a trans-enoyl-CoA. This is the key step in yielding NADH. The subsequent reactions do not produce additional NADH per round of beta-oxidation; rather, they lead to the production of FADH2 and the release of acetyl-CoA.

Understanding this process is critical for appreciating how fats are metabolized in the body and how energy is derived from lipid sources. Thus, the correct understanding of the production of NADH highlights the importance of the first oxidation in the beta-oxidation cycle.