AAMC FL Practice Exam

Which process generates the most ATP during cellular respiration?

1. Glycolysis

2. Krebs cycle

3. Electron transport chain

4. Pyruvate dehydrogenase reaction

The correct answer is: Electron transport chain

The process that generates the most ATP during cellular respiration is the electron transport chain. This stage occurs in the inner mitochondrial membrane and is primarily responsible for the bulk of ATP production. It utilizes the reduced coenzymes NADH and FADH2, which were generated during earlier stages of respiration, including glycolysis and the Krebs cycle. As electrons are transferred through a series of protein complexes in the electron transport chain, protons are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This electrochemical gradient stores potential energy. The enzyme ATP synthase then harnesses this energy as protons flow back into the matrix, catalyzing the conversion of ADP and inorganic phosphate into ATP. This method of ATP production is known as oxidative phosphorylation and is significantly more efficient than the ATP yield from glycolysis or the Krebs cycle, leading to the generation of approximately 26 to 28 ATP molecules from the complete oxidation of one glucose molecule. In contrast, glycolysis contributes a net gain of 2 ATP molecules, while the Krebs cycle directly produces 2 ATP molecules (or GTP) per glucose through substrate-level phosphorylation, and the pyruvate dehydrogenase reaction itself does not generate ATP but rather produces