An electron transport chain (also called electron transport system (ETS) or electron transfer chain (ETC)) is a series of membrane-associated electron carriers mediating biochemical reactions that produce adenosine triphosphate (ATP), which is the energy currency of life

ATP is generated in the cell by energy-releasing processes and is broken down by energy-consuming processes, in this way ATP transfers energy between spatially-separate metabolic reactions. ATP is the main energy source for the majority of cellular functions. This includes the synthesis of macromolecules, including DNA, RNA, and proteins. ATP also plays a critical role in the transport of macromolecules across cell membranes, e.g. exocytosis and endocytosis.

ATP is critically involved in maintaining cell structure by facilitating assembly and disassembly of elements of the cytoskeleton. In a related process, ATP is required for the shortening of actin and myosin filament crossbridges required for muscle contraction.