<P> ATP is made by an enzyme called ATP synthase . Both the structure of this enzyme and its underlying gene are remarkably similar in all known forms of life . </P> <P> ATP synthatase is powered by a transmembrane electrochemical potential gradient, usually in the form of a proton gradient . The function of the electron transport chain is to produce this gradient . In all living organisms, a series of redox reactions is used to produce a transmembrane electrochemical potential gradient, or a so - called proton motive force (pmf). </P> <P> Redox reactions are chemical reactions in which electrons are transferred from a donor molecule to an acceptor molecule . The underlying force driving these reactions is the Gibbs free energy of the reactants and products . The Gibbs free energy is the energy available ("free") to do work . Any reaction that decreases the overall Gibbs free energy of a system will proceed spontaneously (given that the system is isobaric and also adiabatic), although the reaction may proceed slowly if it is kinetically inhibited . </P> <P> The transfer of electrons from a high - energy molecule (the donor) to a lower - energy molecule (the acceptor) can be spatially separated into a series of intermediate redox reactions . This is an electron transport chain . </P>

In its mechanism photophosphorylation is most similar to