The electron transport chain is a system of transmembrane proteins and electron carriers necessary to maintain energy balance.
ETC of mitochondria maintains a balance due to the transfer of electrons and protons from NADH H+ and FADH2 to the electron acceptor. In the case of aerobic respiration, the acceptor may be molecular oxygen (O2). In eukaryotes, the electron transport chain is located in the inner mitochondrial membrane. The electron carriers are arranged in order of decreasing electron affinity according to their redox potential, where the acceptor has the strongest electron affinity. Therefore, electron transport throughout the chain proceeds spontaneously with the release of energy in the form of a proton (H+). Protons from the intermembrane space cross the membrane through the proton pump, where proton potential is induced. The proton potential is converted by ATP synthase to the energy of the chemical bonds of ATP. The conjugate work of ETC and ATP synthase is called oxidative phosphorylation.
The electron transport chain of photosynthesis is a sequence of electron carriers located on the proteins of photosynthetic membranes and carrying out photo-induced electron transport coupled with transmembrane proton transfer against an electrochemical gradient. The electron transport chain of chloroplasts is organized in the membrane of thylakoids and consists of three polypeptide transmembrane protein complexes (Photosystem II, Cytochrome-b6f-complex, Photosystem I), with carriers located on them, and also includes mobile electron carriers (pool of plastoquinones, plastocyanin and ferredoxin ), providing the transport of electrons between the complexes. ETC of photosynthesis provides the transport of electrons along the potential gradient from water to final acceptors with the formation of adenosine triphosphate (ATP) and reduced NADPH H+).