Electron transport chain- Definition, Components, Steps, FAQs


The electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. The ETC is the final stage of cellular respiration, where most of the energy (ATP) is produced from the oxidation of NADH and FADH2, which are the products of previous cycles such as the citric acid cycle, fatty acid oxidation, and amino acid metabolism. The ETC creates an electrochemical gradient of protons across the membrane, which drives the synthesis of ATP by a process called oxidative phosphorylation. The enzyme that catalyzes this process is called ATP synthase, which uses the energy of the proton gradient to convert ADP and phosphate into ATP. The ETC also consumes molecular oxygen (O2) as the final electron acceptor, which is reduced to water (H2O) in the process. This is why aerobic respiration requires oxygen to produce energy. In anaerobic respiration, other molecules such as sulfate or nitrate can act as the final electron acceptors. In eukaryotes, the ETC is located in the inner mitochondrial membrane, which is folded into cristae to increase the surface area for electron transfer. In prokaryotes, the ETC is located in the plasma membrane or in some cases, in specialized membranes called thylakoids. The ETC consists of four major complexes (I-IV) and two mobile electron carriers (coenzyme Q and cytochrome c). Each complex contains multiple protein subunits and cofactors that facilitate the transfer of electrons. The complexes are named according to their order of function in the chain. The ETC can be summarized by the following equation:

NADH + 1/2 O2 + H+ + ADP + Pi → NAD+ + ATP + H2O

Source: Jain JL, Jain S, and Jain N (2005). Fundamentals of Biochemistry. S. Chand and Company. Nelson DL and Cox MM. Lehninger Principles of Biochemistry. Fourth Edition.