MCAT Official Prep (AAMC)
Biology Question Pack, Vol. 1 Passage 13 Question 85
Biology Question Pack, Vol 2. Question 18
• Reduced electron carriers (NADH and FADH2) from other steps of cellular respiration transfer their electrons to molecules near the beginning of the electron transport chain. In the process, they turn back into NAD+ and FAD, which can be reused in other steps of cellular respiration.
• As electrons are passed down the electron transport chain, they move from a higher to a lower energy level, releasing energy. Some of the energy is used to pump hydrogen ions, moving them out of the mitochondrial matrix and into the intermembrane space. This pumping establishes an electrochemical gradient.
• At the end of the electron transport chain, electrons are transferred to molecular oxygen, which splits in half and takes up hydrogen ions to form water.
• As hydrogen ions flow down their gradient and back into the matrix, they pass through an enzyme called ATP synthase, which harnesses the flow of protons to synthesize ATP.
Oxidative phosphorylation: The final stage of cellular respiration where the combined action of the electron transport chain and chemiosmotic coupling result in ATP production.
Electron transport chain: a series of proteins embedded in the inner mitochondrial membrane that takes up highly energetic electrons from NADH and FADH2 and uses the energy to form proton gradient across the membrane.
Chemiosmotic coupling: A process in which the movement of protons across the mitochondrial membrane downward their gradient is coupled to ATP production via phosphorylation of ADP.