Which structure in mitochondria is directly involved in the oxidation of NADH?

The correct answer is the cristae. Cristae are the folds of the inner mitochondrial membrane where the electron transport chain (ETC) occurs. During cellular respiration, NADH, which is produced during glycolysis and the Krebs cycle, donates electrons to the electron transport chain located in the cristae. This process is essential for oxidative phosphorylation, where the energy from these electrons is used to pump protons into the intermembrane space, creating an electrochemical gradient. The flow of protons back into the mitochondrial matrix through ATP synthase drives the production of ATP.

The matrix, while it contains enzymes necessary for the Krebs cycle and the oxidation of pyruvate and fatty acids, is not where NADH is directly oxidized. The outer membrane serves as a boundary for the mitochondrion but does not play a direct role in the oxidation of NADH. The inner membrane, while housing the components of the electron transport chain, refers to the entire membrane structure rather than the specific location where NADH oxidation occurs, which is more specifically associated with the cristae. Thus, the cristae's structure and position are crucial for the efficient functioning of the oxidation process involving NADH.