Electron Transport Chain

The electron transport chain (ETC) is located in the inner mitochondrial membrane and functions only in the presence of oxygen. NADH and FADH2 donate electrons to a series of proteins embedded within the membrane (Bailey, 2019).

As electrons move through the chain, their energy is used to pump protons (Hydrogen ions) into the intermembrane space, creating an electrochemical gradient. This proton gradient drives protons back into the mitochondrial matrix through ATP synthase (Monash University, 2025a).

ATP synthase catalyses the phosphorylation of ADP with inorganic phosphate, generating approximately 26–28 ATP molecules. Oxygen acts as the final electron acceptor, creating water as a waste product (Bailey, 2019).

This stage is why oxygen availability is important for endurance athletes. Without sufficient oxygen, the ETC cannot function, thus reducing ATP output because aerobic respiration cannot function.