mitochondrialna

Mitochondria are double-membrane-bound organelles in most eukaryotic cells. They are the cell’s primary source of ATP through oxidative phosphorylation. The organelle features an outer membrane and a highly folded inner membrane, the cristae, which increase surface area. The mitochondrial matrix contains enzymes of the citric acid cycle, mitochondrial DNA, and ribosomes.

Energy production occurs as electrons pass through the respiratory chain in the inner membrane, pumping protons to generate an electrochemical gradient. ATP synthase uses this gradient to produce ATP from ADP and phosphate. Mitochondria also participate in fatty acid oxidation, heme synthesis, calcium storage, and the generation of reactive oxygen species.

Genetics and dynamics: In humans, mtDNA is a circular molecule of about 16,569 base pairs encoding 13 proteins, 22 tRNAs, and 2 rRNAs. Most mitochondrial proteins are encoded in the nucleus and imported. Mitochondria divide by fission and fuse with other mitochondria; mitophagy removes damaged organelles. Maternally inherited mtDNA and heteroplasmy influence the expression of mitochondrial diseases.

Clinical and research relevance: Mutations in mtDNA or in nuclear genes affecting mitochondria cause mitochondrial diseases with variable symptoms, including muscle weakness and neurological deficits. Mitochondria are implicated in aging and in several common diseases; they are a focus of research on metabolism, apoptosis, and cancer therapy.

Origin and history: The endosymbiotic theory posits that mitochondria arose from ancestral bacteria incorporated into early eukaryotic cells. The term mitochondrion derives from Greek for thread and granule; the organelles were described in the 19th century and named in the late 19th century.