CONCEPT
Mitochondrion
The cellular organelle that produces energy through oxidative phosphorylation — and the paradigmatic case of endosymbiosis, a once-free bacterium now permanently integrated into every eukaryotic cell.
The mitochondrion is the membrane-bound organelle found in nearly all eukaryotic cells, responsible for producing ATP through oxidative phosphorylation — the process that extracts energy from nutrients using oxygen. Each mitochondrion is a descendant of an alpha-proteobacterium engulfed by an archaeal host cell roughly two billion years ago. The bacterium was not digested; it survived, reproduced, and over geological time became so integrated with the host that neither could survive independently. The mitochondrion retains its own genome (approximately thirty-seven genes in humans), its own ribosomes, and a double membrane reflecting the original engulfment. It replicates independently of the host's nuclear DNA, yet its replication is coordinated with cell division. The mitochondrion is Margulis's canonical example of successful endosymbiosis — a partnership so intimate that the partners are no longer separate organisms but components of a larger whole.
In The You On AI Field Guide
Mitochondria were first observed in the 1890s as granular structures within cells, but their function remained mysterious until the mid-twentieth century. The discovery that mitochondria possess