Mitochondrion | Definition, Function, Structure, & Facts | Britannica

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Role in energy production

basic overview of processes of ATP production
basic overview of processes of ATP productionThe three processes of ATP production include glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation. In eukaryotic cells the latter two processes occur within mitochondria. Electrons that are passed through the electron transport chain ultimately generate free energy capable of driving the phosphorylation of ADP.(more)

The outer mitochondrial membrane is freely permeable to small molecules and contains special channels capable of transporting large molecules. In contrast, the inner membrane is far less permeable, allowing only very small molecules to cross into the gel-like matrix that makes up the organelle’s central mass. The matrix contains the deoxyribonucleic acid (DNA) of the mitochondrial genome and the enzymes of the tricarboxylic acid (TCA) cycle (also known as the citric acid cycle, or Krebs cycle), which metabolizes nutrients into by-products the mitochondrion can use for energy production.

Key People: Bruce Ames Albert Claude (Show more) Related Topics: mitochondrial disease mtDNA endosymbiont hypothesis matrix crista (Show more) On the Web: The Royal Society Publishing - Open Biology - Mitochondria—hubs for regulating cellular biochemistry: emerging concepts and networks (Jan. 05, 2026) (Show more) See all related content

The processes that convert these by-products into energy occur primarily on the inner membrane, which is bent into folds known as cristae that house the protein components of the main energy-generating system of cells, the ETC. The ETC uses a series of oxidation-reduction reactions to move electrons from one protein component to the next, ultimately producing free energy that is harnessed to drive the phosphorylation of ADP (adenosine diphosphate) to ATP. This process, known as chemiosmotic coupling of oxidative phosphorylation, powers nearly all cellular activities, including those that generate muscle movement and fuel brain functions.

Mechanism of cellular autophagy, illustration for Nobel Prize Award in Medicine 2016. 3D illustration showing fusion of lysosome with autophagosome containing microbes and molecules. Britannica Quiz Parts of a Cell Quiz

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