Eukaryote Totally Explained

Everything about Eucaryote totally explained

- style="background:#e0d0b0;" Likely cladogram of Eukarya Several authorities recognize two larger clades, the unikonts and the bikonts, that derive from an ancestral uniflagellar organism and a biflagellate respectively. In this system, the opisthokonts and amoebozoans are considered unikonts, and the rest bikonts. The chromalveolates were originally thought to be two separate groups, the chromists and the alveolates, but the former was proved to be paraphyletic to the latter, and the two groups combined. Some small protist groups have not been related to any of these supergroups, in particular the centrohelids.
Eukaryotes are closely related to Archaea, at least in terms of nuclear DNA and genetic machinery, and some place them with Archaea in the clade Neomura. In other respects, such as membrane composition, they're similar to eubacteria. Three main explanations for this have been proposed:

Eukaryotes resulted from the complete fusion of two or more cells, where the cytoplasm formed from a eubacterium, and the nucleus from an archaeon or from a virus.

Eukaryotes developed from Archaea, and acquired their eubacterial characteristics from the proto-mitochondrion.

Eukaryotes and Archaea developed separately from a modified eubacterium. The origin of the endomembrane system and mitochondria are also disputed. The phagotrophic hypothesis states the membranes originated with the development of endocytosis and later specialized; mitochondria were acquired by ingestion, like plastids. The syntrophic hypothesis states that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it; the membranes originate later, in part thanks to mitochondrial genes (the hydrogen hypothesis is one particular version).
In a study using genomes to construct supertrees, Pisani et al (2007) suggest that, along with evidence that there was never a mitochondrion-less eukaryote, eukaryotes evolved from a syntrophy between an archaea closely related to Thermoplasmatales and an α-proteobacterium, likely a symbiosis driven by sulfur or hydrogen. The mitochondrion and its genome is a remnant of the α-proteobacterial endosymbiont.

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