Operational definition
Energy-conversion mechanism.
The coupling of an exergonic oxidation–reduction reaction to the creation of a biologically conserved energetic state.
Electrons move from a donor to an acceptor, and some of the associated decrease in Gibbs free energy is conserved as:
- an ion gradient;
- ATP;
- reduced cofactors;
- activated chemical intermediates.
The remainder is dissipated, principally as heat.
22.1 Substrate oxidation
An electron donor is oxidized.
22.2 Electron transfer
Electrons pass through:
- soluble carriers
- membrane complexes
- quinone pools
- cytochromes
- iron–sulfur proteins
- extracellular conduits
22.3 Terminal reduction
An electron acceptor is reduced.