AAMC FL Practice Exam

What two processes comprise oxidative phosphorylation?

1. Glycolysis and substrate-level phosphorylation

2. Electron transport chain and chemiosmosis

3. Krebs cycle and electron transport chain

4. Fermentation and gluconeogenesis

The correct answer is: Electron transport chain and chemiosmosis

Oxidative phosphorylation consists of two main processes: the electron transport chain and chemiosmosis. The electron transport chain involves a series of protein complexes located in the inner mitochondrial membrane that transfer electrons derived from NADH and FADH2 through a series of redox reactions. This process creates a proton gradient (higher concentration of protons outside the mitochondrial matrix) as electrons move through the chain, which is vital for the subsequent function of chemiosmosis. Chemiosmosis is the process wherein the energy stored in the proton gradient is used to synthesize ATP. Protons flow back into the mitochondrial matrix through ATP synthase, a process that drives the conversion of ADP and inorganic phosphate into ATP. This coupling of electron transport and ATP synthesis is what defines oxidative phosphorylation. The other options represent different metabolic pathways that do not describe the processes involved in oxidative phosphorylation.