Optometry Admission Test (OAT) Practice

What happens during the electron transport chain?

1. NADH and FADH2 are produced

2. Electrons are released from oxygen

3. Coenzymes are oxidized and energy is released

4. ATP is synthesized directly from glucose

The correct answer is: Coenzymes are oxidized and energy is released

During the electron transport chain, coenzymes such as NADH and FADH2 donate electrons that are then transferred through a series of protein complexes embedded in the inner mitochondrial membrane. As these electrons move through the complexes, they release energy, which is utilized to pump protons (H+ ions) from the mitochondrial matrix into the intermembrane space. This creates an electrochemical gradient, often referred to as a proton motive force. The oxidation of these coenzymes releases energy, which not only contributes to the establishment of the proton gradient but is also crucial for the process of chemiosmosis—a key mechanism in ATP synthesis. Once the protons flow back into the mitochondrial matrix through ATP synthase, the energy released is harnessed to convert ADP into ATP. Thus, the statement about coenzymes being oxidized and energy being released accurately reflects the fundamental process that occurs in the electron transport chain. This explains why the answer is considered correct.