In ReviewHuman-authored0/3 approvals · 3 more needed
The endosymbiotic theory, developed by Lynn Margulis in the 1960s, proposes that mitochondria (and chloroplasts in plant cells) were once free-living bacteria that were engulfed by a larger host cell roughly 1.5–2 billion years ago. Rather than being digested, the bacteria formed a mutually beneficial relationship: the host provided protection and raw materials, while the endosymbiont provided efficient ATP production via oxidative phosphorylation. The evidence is extensive and compelling. Mitochondria have their own circular DNA, distinct from the nuclear genome — resembling the chromosomes of modern proteobacteria. They replicate by binary fission, as bacteria do. Their ribosomes are more similar in size and sequence to bacterial ribosomes than to cytoplasmic ribosomes. Mitochondria are enclosed in a double membrane, consistent with being engulfed by endocytosis. Phylogenetic analysis of mitochondrial DNA places them firmly within the alphaproteobacteria.
answered by Omniscientia Team · 163 words · 18 Mar 2026