Endosymbiotic theory

Endosymbiotic theory holds that mitochondria and chloroplasts originated as free-living bacteria that entered ancestral eukaryotic cells and became permanent residents.

Mitochondrion: A membrane-bound organelle that produces most of a eukaryotic cell’s usable energy through cellular respiration. Mitochondria are the best-established organelles explained by an ancient bacterial partnership.
Lynn Margulis: An American biologist who championed the modern development of endosymbiotic theory. Margulis assembled evidence and argued forcefully for the theory’s acceptance.
Endosymbiosis: A relationship in which one organism lives inside another organism. The theory proposes that a long-term endosymbiosis became an organelle.
Glaucophyte: A group of freshwater algae whose plastids retain features associated with their bacterial ancestry. Their plastids preserve peptidoglycan between membranes, an unusual clue to plastid origins.
Chloroplast: A photosynthetic organelle in plants and algae that converts light energy into chemical energy. Chloroplasts trace to photosynthetic bacteria incorporated into eukaryotic ancestors.
Mitochondrial endosymbiosis: The evolutionary incorporation of an aerobic bacterium into the ancestor of mitochondria. This ancient event established the energy-producing partnership central to eukaryotic evolution.
Eukaryote: An organism whose cells contain a nucleus and other membrane-bound compartments. The theory concerns how key compartments of eukaryotic cells originated.
Paulinella chromatophora: A freshwater amoeba whose photosynthetic chromatophores evolved from cyanobacteria relatively recently. It provides a rare example of a comparatively recent primary endosymbiosis.
Mitochondrial DNA: The genetic material contained within mitochondria, usually inherited from one parent in animals. Its separate genome is a surviving trace of mitochondria’s bacterial ancestry.
Primary endosymbiosis: The incorporation of a free-living prokaryote directly into a eukaryotic cell. Primary endosymbiosis describes the origin of mitochondria and the first plastids.

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