Your mitochondria used to be free
Mitochondria descend from bacteria that took up residence inside another cell. They still carry their own circular genome.
Established2 min read
Margulis argued in 1967 that organelles were endosymbionts. The mitochondrial chromosome is circular, bacterial in style, and codes for pieces of the respiratory chain. The ribosomes inside the organelle look bacterial. Phylogenies put the ancestor among the alphaproteobacteria.
Most of the old bacterial genes have moved to the nucleus. The organelle cannot go back to a pond. The partnership is about two billion years old and is the reason complex cells have the energy budget they do. Every breath is a bacterial reaction, hosted.
Caveats
- The host cell’s identity — an archaeon, on current evidence — is a live research front. The bacterial origin of the mitochondrion is not.
Sources
- 1Sagan L. (Margulis). On the Origin of Mitosing Cells. Journal of Theoretical Biology 14, 1967.