The electron transport chain (ETC) is the final stage of cellular respiration, occurring within the mitochondria. It involves a series of protein complexes that facilitate the transfer of electrons from NADH and FADH2 to molecular oxygen. This electron transfer releases energy, which is then used to pump protons (H+) across the inner mitochondrial membrane, creating an electrochemical gradient. This gradient, also known as the proton-motive force, is a form of potential energy.
The energy stored in the proton-motive force is harnessed by ATP synthase, an enzyme that allows protons to flow back across the membrane down their electrochemical gradient. As protons pass through ATP synthase, the enzyme rotates, catalyzing the phosphorylation of ADP to ATP. This process is called oxidative phosphorylation and is the primary mechanism by which cells generate the majority of their ATP. Understanding the efficiency of this process is crucial for comprehending cellular energy budgets and metabolic regulation. Historically, estimations varied, but current research provides more refined values.
