Biochemistry Module 2 Practice Test

Shuttling electrons to the electron transport chain is done by reduced coenzymes that carry high-energy electrons from earlier metabolic steps. The main players are NADH and FADH2. During processes like glycolysis, the pyruvate dehydrogenase step, and beta-oxidation, electrons are captured by NAD+ to form NADH and by FAD to form FADH2. These reduced cofactors then deliver their electrons to the chain—NADH donates to Complex I and becomes NAD+, while FADH2 donates to Complex II and becomes FAD. As electrons move through the chain, protons are pumped across the inner mitochondrial membrane, creating the gradient that drives ATP synthesis via ATP synthase. CoA carries acyl groups rather than electrons to the chain, ATP is the energy currency, and glucose is a substrate that must be oxidized to release electrons; it does not directly shuttle electrons to the chain.