The series of proteins in which high-energy electrons from the Krebs cycle are used to convert ADP into ATP is called the

• A. Electron transport chain
• B. Glycolysis
• C. Krebs cycle
• D. Fermentation

Answer: (A)

The main idea is oxidative phosphorylation, where high-energy electrons carried by NADH and FADH2 move through a sequence of protein complexes embedded in the inner mitochondrial membrane. As electrons pass along this electron transport chain, their energy powers the pumping of protons across the membrane, creating a proton gradient. When protons flow back through ATP synthase, that flow drives the conversion of ADP and inorganic phosphate into ATP. This chain of proteins is where the actual ATP production via respiration happens, using electrons originating from the Krebs cycle.

The Krebs cycle itself supplies those high-energy electrons, but the chain is the stage that uses their energy to generate ATP. Glycolysis occurs in the cytoplasm and yields some ATP by substrate-level phosphorylation, not by transferring electrons through an electron transport chain. Fermentation also doesn't involve the mitochondrial electron transport chain and produces ATP without using the chain’s proton-motive forces.