Eukaryogenesis

Eukaryogenesis is the evolutionary process in which the first eukaryotic cell arose from prokaryotic ancestors. It produced cells with a nucleus, internal membranes and mitochondria, and it is one of the major transitions in the history of life.

The host cell was an archaeon, probably related to the Asgard archaea, and the partner was a bacterium that became the mitochondrion, as described in endosymbiotic theory. Fossil and molecular clock evidence suggest that the process was complete somewhere between about 1.8 and 2.7 billion years ago, after oxygen began to rise in the Great Oxidation Event.

In "mitochondria-late" models, a nucleated cell developed first and then took in the bacterium. In "mitochondria-early" models, the partnership came first and drove the rest, for example by supplying energy that allowed a big expansion of the genome. Newer syntrophy models propose that the host and its partner began by sharing hydrogen and other by-products, with the partner's cell slowly moving inside.

Energy made in mitochondria allowed eukaryotes to carry far larger genomes, to build the endomembrane system and the cytoskeleton, and eventually to become multicellular. All living eukaryotes descend from a common ancestor that had these features, called the last eukaryotic common ancestor, which lived after the last universal common ancestor of all cells.

• Endosymbiotic Theory — how mitochondria arose
• Asgard Archaea — the closest archaeal relatives
• Eukaryote — the resulting cell type