Editing Symbiogenesis (section)

=== Nuclear membrane ===

The presence of a nucleus is one major difference between eukaryotes and [[prokaryote]]s.<ref>{{Cite web |url=https://www.nature.com/scitable/content/typical-prokaryotic-left-and-eukaryotic-right-cells-14665031 |title=Typical prokaryotic (left) and eukaryotic (right) cells: Learn Science at Scitable |website=www.nature.com |access-date=2019-03-24}}</ref> Some conserved [[nuclear protein]]s between eukaryotes and prokaryotes suggest that these two types had a common ancestor.<ref>{{cite journal |last1=Devos |first1=Damien P. |last2=Gräf |first2=Ralph |last3=Field |first3=Mark C. |title=Evolution of the nucleus |journal=[[Current Opinion in Cell Biology]] |volume=28 |pages=8–15 |date=June 2014 |issue=100 |pmid=24508984 |pmc=4071446 |doi=10.1016/j.ceb.2014.01.004 }}</ref> Another theory behind nucleation is that early nuclear membrane proteins caused the [[cell membrane]] to fold and form a sphere with pores like the [[nuclear envelope]].<ref>{{cite journal |last1=Wilson |first1=Katherine L. |last2=Dawson |first2=Scott C. |title=Evolution: functional evolution of nuclear structure |journal=[[Journal of Cell Biology]] |volume=195 |issue=2 |pages=171–81 |date=October 2011 |pmid=22006947 |pmc=3198171 |doi=10.1083/jcb.201103171 }}</ref>
As a way of forming a nuclear membrane, endosymbiosis could be expected to use less energy than if the cell was to develop a metabolic process to fold the cell membrane for the purpose.<ref name=":3"/> Digesting engulfed cells without energy-producing mitochondria would have been challenging for the host cell.<ref name=":2"/> On this view, membrane-bound bubbles or [[Vesicle (biology and chemistry)|vesicles]] leaving the protomitochondria may have formed the nuclear envelope.<ref name=":2"/>

The process of symbiogenesis by which the early [[eukaryote|eukaryotic cell]] integrated the proto-[[mitochondrion]] likely included protection of the [[archaea]]l host [[genome]] from the release of [[reactive oxygen species]]. These would have been formed during [[oxidative phosphorylation]] and ATP production by the proto-mitochondrion. The [[nuclear envelope|nuclear membrane]] may have evolved as an adaptive innovation for protecting against nuclear genome [[DNA damage (naturally occurring)|DNA damage]] caused by reactive oxygen species.<ref>{{cite book |last1=Bernstein |first1=H. |last2=Bernstein |first2=C. |chapter=Sexual communication in archaea, the precursor to meiosis |pages=103–117 |title=Biocommunication of Archaea |editor=Witzany, G. |date=2017 |publisher=Springer International Publishing |isbn=978-3-319-65535-2 |doi=10.1007/978-3-319-65536-9 |s2cid=26593032 }}</ref> Substantial transfer of genes from the ancestral proto-mitochondrial genome to the nuclear genome likely occurred during early eukaryotic evolution.<ref name="pmid12893934">{{cite journal |last1=Gabaldón |first1=T. |last2=Huynen |first2=M. A. |title=Reconstruction of the proto-mitochondrial metabolism |journal=Science |volume=301 |issue=5633 |pages=609 |date=August 2003 |pmid=12893934 |doi=10.1126/science.1085463 |s2cid=28868747 }}</ref> The greater protection of the nuclear genome against reactive oxygen species afforded by the nuclear membrane may explain the adaptive benefit of this gene transfer.