Inner mitochondrial membrane contains groups of electron and proton transporting enzymes. In each group the enzymes are arranged in a specific series called electron transport chain or mitochondrial respiratory chain. An electron transport chain or system is a series of coenzymes and cytochromes that take part in the passage of electrons from a chemical to its ultimate acceptor. The passage of electrons from one enzyme or cytochrome to the next is a downhill journey with a loss of energy at each step. At each step the electron carriers include flavins, iron sulphur complexes, quinones and cytochromes.
Electron transport chain of cell is present in the innermitochondrial membrane. It is madeup of four different complexes. They are arranged in the increasing order of their redoxpotential. So electrons flow from one end to the other ( ie from complex one to complex 4) and ultimately given to molecular oxygen which is reduced to water.
During the flow of electrons along the electron transport chain it pumps out protons from mitochondrial matrix to intermembraneous space creating an electrochemical potential. Protons present in the intermembraneous space now reenters the mitochondria with the help of a seperate proten called as ATP Synthase. re-entry of protons into the mitochondrial matrix vis ATP Synthase protein is coupled to phosphorylation of ADP to form ATP. This is called Oxidative phosphorylation. It is a major mechanism by which animal cells obtain chemical energy - ATP.
Electron transport chains are the cellular mechanisms. It is used for extracting energy from sunlight in photosynthesis. In electron transport chain a series of redox reactions occurred in which electrons are transferred from a donor molecule to an acceptor molecule. This chain produces a trans membrane proton electrochemical gradient.
Light, derives the conversion of water to oxygen and NADP+ to NADPH and transfer of H+ ions across chloroplast membrane, in chloroplasts. In mitochondria, it is the conversion of oxygen to water and NADH to NAD+ and succinate to fumarate. The electron transport chain comprises an enzymatic series of electron donors and acceptors.