An<unk>  associates<unk>  carriers (such as NADH and FADH2) and  mediating biochemical reactions that produce adenosine triphosphate (ATP), which is a major energy intermediate in living organisms. Only two sources of energy are available to biosynthesize organic molecules and maintain biochemical and kinetic processes in living organisms: oxidation-reduction (redox) reactions and some forms of radiation, such as sunlight (used for photosynthesis). Organisms that use redox reactions to produce ATP are called chemotrophs. Organisms that use sunlight are called phototrophs.  Both chemotrophs and phototrophs use<unk> s to convert energy into ATP. This is achieved through a three-step process:
Electron transport chain
Oxidative phosphorylation
ATP synthase
Malate-aspartate shuttle
Pyruvate dehydrogenase complex
Fatty acid metabolism
Cellular respiration
Ubiquinol oxidase