Foundations of Biology of Exam 1 Practice Test

Re-oxidation of electron carriers refers to NADH and FADH2 donating their electrons to the electron transport chain, regenerating NAD+ and FAD for more rounds of metabolism. The energy released as those electrons move through the chain powers proton pumping across a membrane, creating a proton gradient. ATP synthase then uses this gradient to convert ADP and inorganic phosphate into ATP. This coupling of electron transfer to ATP production is what oxidative phosphorylation is all about.

Substrate-level phosphorylation makes ATP directly in glycolysis and the citric acid cycle without needing the electron transport chain. Fermentation re-oxidizes NADH by transferring electrons to an organic molecule like pyruvate, regenerating NAD+, but it bypasses the electron transport chain and yields much less ATP. Hence, the re-oxidation of electron carriers is linked to oxidative phosphorylation.