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Mechanistics explained in literature II: Textual explanations

Since I see unsurmountable problems in a mechanistic scenario for the origin of mitochondria, I am interested how the proponents of the endosymbiotic theory explain the mechanistic steps leading from a bacterial symbiont to the organelle we see now. Everytime I encounter an explanation, I will put it here, but so far, I haven’t been able to find a scenario that goes beyond the ‘an unknown host swallowed an unknown primitive bacterium which gave rise to the mitochondrium’ type of explanations. This post is complemented by the Figures on the mechanisms.

It is now generally agreed that mitochondria evolved from free-living alpha-proteobacteria following a single endosymbiotic event around two billion years ago [15–18]. Since that time, eukaryotic cells have diversified into the many forms seen today. The evolution of mitochondria has resulted in the loss from yeast and all higher eukaryotes of the prokaryotic genes originally involved in division of the symbiont.[…]During the course of evolution all mitochondrial-type FtsZ genes identified to date transferred from the mitochondrial genome to the nucleus and are now targeted back to mitochondria (Logan, 2006).

It is thought that mitochondria arose by way of a single endosyrnbiotic event in which a pre-eukaryotic cell engulfed an a-proteobacterium. This event led to a symbiotic relationship wherein each member (host and prey) became dependent on the other (reviewed in Gray et al., 1999: Lang et a l , 1999a). Subsequent migration of mtDNA genes to the nucleus, mtDNA rearrangement and loss of mitochondrial genes due to loss of a particular mitochondrial function have resulted in pronounced diversity of mitochondrial genome structure and organization among the eukaryotic lineages (John E Norman).


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