Mitochondria are sites of

Mitochondria are sites of Oxidative phosphorylation.
The breakdown of carbohydrates or fats is derived from oxidative phosphorylation, which takes place within mitochondria.
As the production of reactive oxygen species by these proton-pumping complexes is greatest at high membrane potentials, it has been proposed that mitochondria regulate their activity to maintain the membrane potential within a narrow range that balances ATP production against oxidant generation.