Final answer:
The electron transport chain consists of proteins that use energy from electrons transferred from NADH to actively pump H+ ions across the mitochondrial membrane, creating an electrochemical gradient used by ATP synthase to produce ATP.
Step-by-step explanation:
Understanding the Electron Transport Chain and H+ Ion Pumping
During aerobic respiration, proteins embedded in the cristae act as pumps in the electron transport chain (ETC), which is located in the inner mitochondrial membrane. High-energy electrons from NADH are transferred to the ETC, and as the electrons move from one carrier to the next, their energy is utilized to pump hydrogen ions (H+) from the mitochondrial matrix into the intermembrane space. This creates an electrochemical gradient essential for ATP synthesis.
The initial transfer of an electron from NADH to the ETC occurs when NADH is oxidized, releasing an electron and a H+ ion. Subsequent carriers in the chain are alternately reduced as they accept electrons and oxidized when they pass the electrons on to the next carrier. The transported electrons eventually reach molecular oxygen, which is reduced to water in the process. Throughout this series of reactions, the energy released is strategically used to pump H+ ions across the inner membrane, establishing a gradient for ATP production.
Oxidative phosphorylation is the process in which the stored energy in the gradient, resulting from the active transport of H+ ions by the ETC, is harnessed by the enzyme ATP synthase to generate ATP. This is accomplished when H+ ions flow back into the matrix through ATP synthase, driven by the gradient. The proton motive force generated is a consequence of the electron transport chain activity, causing chemiosmosis and ultimately leading to ATP synthesis.