Mitochondria were acquired “early” during eukaryogenesis.

According to ‘mito-early’ arguments, mitochondria were acquired early during eukaryogenesis and are credited for much of the complexity unique to eukaryotes (i.e. nucleus, ability to express more genes, etc).
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Mitochondria were acquired “late” during eukaryogenesis.

According to ‘mito-late’ arguments, mitochondria were not acquired until much later in the process of eukaryogenesis where certain characteristics unique to eukaryotes were already present.
Created at: 
2020-04-21
  Updated at: 
2020-04-22
Curator:
Ross L.   Subscribe ...

Background

Phylogenetic evidence of when mitochondria were acquired during eukaryogenesis.

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Phylogenetic evidence supports mitochondria being acquired ‘early’ during eukaryogenesis.

eThe author questioned the results of a Nature publication that concluded mitochondria were acquired late during eukaryogenesis by showing phylogenetically that the eukaryotic proteins that were concluded to have non-alphabacterial origins in the Nature publication actually can be traced back to proteobacteria (ancestor of mitochondria).

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Phylogenetic evidence supports mitochondria being acquired ‘late’ during eukaryogenesis.

eThe authors presented phylogenetic evidence showing protein sequences of alphaproteobacterial origin (ancestor of mitochondria) were added to the eukaryotic genome later than genes of other prokaryotic origin.

Archezoan hypothesis: an outdated idea that sought to explain why there are amitochondriate eukaryotes.

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The Archezoan hypothesis was proven to be false after genes within the proposed “archezoans” were traced back to mitochondrial origins.

eThe author examined the Archezoan hypothesis and showed that its premises are false after research showed “archezoan’s” with genes that were acquired after an endosymbiotic event with mitochondria.

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The Archezoan hypothesis provides a theory of how eukaryotic cells may have arisen from a lineage that were amitochondriate.

ehe author proposed the Archezoa hypothesis with evidence arguing for the splitting of the kingdom Eukarya into two subdivisions, one which obtained a mitochondrion, and one which never obtained such an endosymbiont.

The Hydrogen Hypothesis.

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The hydrogen hypothesis speculates that the origin of eukaryogenesis was dependent on conversion to an H2-based metabolism by an endosymbiotic event.

eThe authors proposed a hypothesis where the host cell from an endosymbiotic event became dependent upon the H2 aproduced by the symbiont as an energy source as a way of adapting to a disruption of natural H2 from the environment.

Origin of Introns.

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The origin of introns and the nucleus during eukaryogenesis may have been initiated by an endosymbiotic event.

eThe endosymbiotic event of an alpha-proteobacteria coming to reside in the cytosol of a host cell eventually led to the formation of a proto-nucleus in order for the splicing of introns to occur separately from the translation of mRNA.

The energetics of obtaining mitochondria.

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Mitochondria allow the eukaryotic cell to push past an energy threshold that inhibits prokaryotic cells.

eAn endosymbiotic event of a prokaryote engulfing an ancestor of mitochondria led to a fitness landscape change where eukaryotes had an increased “energy budget” allowing them to express exponentially more genes than a prokaryotic cell.