Mitochondrial

Mitochondrial refers to mitochondria, the energy-producing organelles in most eukaryotic cells. They generate most cellular ATP through oxidative phosphorylation, using substrates from carbohydrate and fat metabolism. Mitochondria are bounded by two membranes, with the inner membrane folded into cristae to increase surface area for the electron transport chain.

The mitochondrial matrix houses enzymes of the tricarboxylic acid cycle and the mitochondrial genome. Mitochondria contain their own circular DNA and ribosomes, a vestige of their endosymbiotic origin from ancestral bacteria. Most mitochondrial proteins are encoded in the nucleus and imported into the organelle.

Key functions include ATP production, regulation of metabolic pathways, calcium storage, and roles in apoptosis and immune signaling. Mitochondria also contribute to heat generation in brown adipose tissue via proton leak and to generation of reactive oxygen species that participate in signaling.

Genetically, mitochondrial DNA (mtDNA) is usually inherited maternally and is separate from nuclear DNA. In humans it is a circular genome about 16,500 base pairs long and encodes 37 genes (13 proteins of the electron transport chain, 22 tRNAs, and 2 rRNAs).

Mutations in mtDNA or in nuclear genes that affect mitochondrial function can cause mitochondrial diseases, often affecting high-energy-demand tissues such as brain and muscle. Features vary and can include progressive weakness, neurologic impairment, and optic neuropathy; diagnosis relies on genetic testing and functional studies.

Evolutionarily, mitochondria arose from endosymbiotic bacteria; their study informs phylogenetics and forensic analysis of maternal lineages. Ongoing research explores mitochondrial biogenesis, dynamics, and therapeutic approaches for mitochondrial disorders.