A group of compounds that pass electron from one to another via redox reactions coupled with the transfer of proton across a membrane to create a proton gradient that drives ATP synthesis
The electron transport chain, as the name implies, is a series of compounds in a chain transferring electron from one to the other through redox reactions. It is coupled with the transfer of proton (H+ ion) across the membrane resulting in the creation of a proton gradient, which is essential in the synthesis of energy-storing compounds, e.g. ATP. Thus, the electron transport chain is a crucial cellular machinery for its major role in extracting energy via redox reactions in cellular respiration as well as in photosynthesis. The electron transport chain is comprised chiefly of electron donors and acceptors.
In eukaryotes, the electron transport chain can be found in the inner mitochondrial membrane where it serves as the site of oxidative phosphorylation. It is also found in the thylakoid membrane of the chloroplast in photosynthetic organisms.
In bacteria, the electron transport chain is located in their cell membrane.