Editing Mitochondrion (section)

== <span class="anchor" id="origin_and_evolution_anchor">Origin and evolution</span>==
{{Main|Symbiogenesis}}

There are two hypotheses about the origin of mitochondria: [[endosymbiotic theory|endosymbiotic]] and [[autotransplantation|autogenous]]. The endosymbiotic hypothesis suggests that mitochondria were originally [[Prokaryote|prokaryotic]] cells, capable of implementing oxidative mechanisms that were not possible for eukaryotic cells; they became [[endosymbiont]]s living inside the eukaryote.<ref name="Gabaldón-2021"/><ref name="McCutcheon-2021">{{cite journal | vauthors = McCutcheon JP | title = The Genomics and Cell Biology of Host-Beneficial Intracellular Infections | journal = Annual Review of Cell and Developmental Biology | volume = 37 | issue = 1 | pages = 115–142 | date = October 2021 | pmid = 34242059 | doi = 10.1146/annurev-cellbio-120219-024122 | doi-access = free }}</ref><ref name="Callier-2022">{{cite journal |last1=Callier |first1=Viviane |title=Mitochondria and the origin of eukaryotes |journal=Knowable Magazine |date=8 June 2022 |doi=10.1146/knowable-060822-2 |doi-access=free }}</ref><ref name="Margulis-1986">{{cite book | vauthors = Margulis L, Sagan D |year= 1986 |title= Origins of Sex: Three billion years of genetic recombination |location= New Haven, CT |publisher= Yale University Press |pages= [https://archive.org/details/originsofsexthre00marg/page/69 69–71, 87] |isbn= 978-0300033403 |url= https://archive.org/details/originsofsexthre00marg/page/69 }}</ref> In the autogenous hypothesis, mitochondria were born by splitting off a portion of DNA from the nucleus of the eukaryotic cell at the time of divergence with the prokaryotes; this DNA portion would have been enclosed by membranes, which could not be crossed by proteins. Since mitochondria have many features in common with [[bacteria]], the endosymbiotic hypothesis is the more widely accepted of the two accounts.<ref name="Margulis-1986"/><ref>{{cite book | vauthors = Martin WF, Müller M | year = 2007 | title = Origin of mitochondria and hydrogenosomes | publisher = Springer Verlag | location = Heidelberg, DE }}</ref>

A [[Mitochondrial DNA|mitochondrion contains DNA]], which is organized as several copies of a single, usually [[Mitochondrial DNA#Circular versus linear|circular]] [[chromosome]]. This mitochondrial chromosome contains genes for [[redox]] proteins, such as those of the respiratory chain. The [[CoRR hypothesis]] proposes that this co-location is required for redox regulation. The mitochondrial [[genome]] codes for some [[RNA]]s of [[ribosome]]s, and the 22&nbsp;[[tRNA]]s necessary for the translation of [[mRNA]]s into protein. The circular structure is also found in prokaryotes. The [[proto-mitochondrion]] was probably closely related to genus ''[[Rickettsia]]'', which is in class Alphaproteobactera of phylum Pseudomonadota.<ref>{{cite journal | vauthors = Emelyanov VV | title = Mitochondrial connection to the origin of the eukaryotic cell | journal = European Journal of Biochemistry | volume = 270 | issue = 8 | pages = 1599–1618 | date = April 2003 | pmid = 12694174 | doi = 10.1046/j.1432-1033.2003.03499.x | doi-access = free }}</ref><ref>{{cite journal | vauthors = Müller M, Martin W | title = The genome of Rickettsia prowazekii and some thoughts on the origin of mitochondria and hydrogenosomes | journal = BioEssays | volume = 21 | issue = 5 | pages = 377–381 | date = May 1999 | pmid = 10376009 | doi = 10.1002/(sici)1521-1878(199905)21:5<377::aid-bies4>3.0.co;2-w }}</ref> However, the exact relationship of the ancestor of mitochondria to the [[alphaproteobacteria]] and whether the mitochondrion was formed at the same time or after the nucleus, remains controversial.<ref>{{cite journal | vauthors = Gray MW, Burger G, Lang BF | title = Mitochondrial evolution | journal = Science | volume = 283 | issue = 5407 | pages = 1476–1481 | date = March 1999 | pmid = 10066161 | pmc = 3428767 | doi = 10.1126/science.283.5407.1476 | bibcode = 1999Sci...283.1476G }}</ref> For example, it has been suggested that the [[SAR11 clade]] of bacteria shares a relatively recent common ancestor with the mitochondria,<ref>{{cite journal | vauthors = Thrash JC, Boyd A, Huggett MJ, Grote J, Carini P, Yoder RJ, Robbertse B, Spatafora JW, Rappé MS, Giovannoni SJ | title = Phylogenomic evidence for a common ancestor of mitochondria and the SAR11 clade | journal = Scientific Reports | volume = 1 | issue = 1 | pages = 13 | date = June 14, 2011 | pmid = 22355532 | pmc = 3216501 | doi = 10.1038/srep00013 | bibcode = 2011NatSR...1...13T }}</ref> while [[phylogenomic]] analyses indicate that mitochondria evolved from a [[Pseudomonadota]] lineage that is closely related to or a member of [[alphaproteobacteria]].<ref name="Martijn-2018">{{cite journal | vauthors = Martijn J, Vosseberg J, Guy L, Offre P, Ettema TJ | title = Deep mitochondrial origin outside the sampled alphaproteobacteria | journal = Nature | volume = 557 | issue = 7703 | pages = 101–105 | date = May 2018 | pmid = 29695865 | doi = 10.1038/s41586-018-0059-5 | bibcode = 2018Natur.557..101M | doi-access = free | hdl = 1874/373336 }}</ref><ref>{{cite journal | vauthors = Fan L, Wu D, Goremykin V, Xiao J, Xu Y, Garg S, Zhang C, Martin WF, Zhu R | title = Phylogenetic analyses with systematic taxon sampling show that mitochondria branch within Alphaproteobacteria | journal = Nature Ecology & Evolution | volume = 4 | issue = 9 | pages = 1213–1219 | date = September 2020 | pmid = 32661403 | doi = 10.1038/s41559-020-1239-x | bibcode = 2020NatEE...4.1213F | biorxiv = 10.1101/715870 }}</ref> Some papers describe mitochondria as sister to the alphaproteobactera, together forming the sister the marineproteo1 group, together forming the sister to [[Magnetococcidae]].<ref>{{cite journal | vauthors = Wang S, Luo H | title = Dating Alphaproteobacteria evolution with eukaryotic fossils | journal = Nature Communications | volume = 12 | issue = 1 | pages = 3324 | date = June 2021 | pmid = 34083540 | pmc = 8175736 | doi = 10.1038/s41467-021-23645-4 | bibcode = 2021NatCo..12.3324W }}</ref><ref>{{cite journal |vauthors=Esposti MD, Geiger O, Sanchez-Flores A |date=May 16, 2022 |title=On the bacterial ancestry of mitochondria: New insights with triangulated approaches |journal=bioRxiv |pages=2022.05.15.491939 |doi=10.1101/2022.05.15.491939 }}</ref><ref>{{cite journal | vauthors = Muñoz-Gómez SA, Susko E, Williamson K, Eme L, Slamovits CH, Moreira D, López-García P, Roger AJ | title = Site-and-branch-heterogeneous analyses of an expanded dataset favour mitochondria as sister to known Alphaproteobacteria | journal = Nature Ecology & Evolution | volume = 6 | issue = 3 | pages = 253–262 | date = March 2022 | pmid = 35027725 | doi = 10.1038/s41559-021-01638-2 | bibcode = 2022NatEE...6..253M }}</ref><ref>{{cite journal | vauthors = Schön ME, Martijn J, Vosseberg J, Köstlbacher S, Ettema TJ | title = The evolutionary origin of host association in the Rickettsiales | journal = Nature Microbiology | volume = 7 | issue = 8 | pages = 1189–1199 | date = August 2022 | pmid = 35798888 | pmc = 9352585 | doi = 10.1038/s41564-022-01169-x }}</ref>

{{Clade|{{Clade
|state1=double
|1='' ''
|label2=[[Alphaproteobacteria|Alphaproteobacteria s.l.]]
|2={{Clade
|1=[[Magnetococcales]]
|2={{clade
|1=[[MarineProteo1]]
|2={{clade
|1='''Mitochondria'''
|2=[[Alphaproteobacteria|Alphaproteobacteria s.s.]]
}}
}}
}}
}}|label1=[[Proteobacteria]]|style=font-size:75%;line-height:75%}}

The ribosomes coded for by the mitochondrial DNA are similar to those from bacteria in size and structure.<ref name="O'Brien-2003">{{cite journal | vauthors = O'Brien TW | title = Properties of human mitochondrial ribosomes | journal = IUBMB Life | volume = 55 | issue = 9 | pages = 505–513 | date = September 2003 | pmid = 14658756 | doi = 10.1080/15216540310001626610 }}</ref> They closely resemble the bacterial [[Ribosome#Structure|70S]] ribosome and not the [[Ribosome#Structure|80S]] [[cytoplasm]]ic ribosomes, which are coded for by [[Cell nucleus|nuclear]] DNA.

The [[endosymbiotic]] relationship of mitochondria with their host cells was popularized by [[Lynn Margulis]].<ref>{{cite journal | vauthors = Sagan L | title = On the origin of mitosing cells | journal = Journal of Theoretical Biology | volume = 14 | issue = 3 | pages = 255–274 | date = March 1967 | pmid = 11541392 | doi = 10.1016/0022-5193(67)90079-3 | bibcode = 1967JThBi..14..225S }}</ref> The [[Endosymbiotic theory|endosymbiotic hypothesis]] suggests that mitochondria descended from aerobic bacteria that somehow survived [[endocytosis]] by another cell, and became incorporated into the [[cytoplasm]]. The ability of these bacteria to conduct [[Cellular respiration|respiration]] in host cells that had relied on [[glycolysis]] and [[Fermentation (biochemistry)|fermentation]] would have provided a considerable evolutionary advantage. This symbiotic relationship probably developed 1.7 to 2 billion years ago.<ref>{{cite journal | vauthors = Emelyanov VV | title = Rickettsiaceae, rickettsia-like endosymbionts, and the origin of mitochondria | journal = Bioscience Reports | volume = 21 | issue = 1 | pages = 1–17 | date = February 2001 | pmid = 11508688 | doi = 10.1023/A:1010409415723 }}</ref><ref>{{cite journal | vauthors = Feng DF, Cho G, Doolittle RF | title = Determining divergence times with a protein clock: update and reevaluation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 94 | issue = 24 | pages = 13028–13033 | date = November 1997 | pmid = 9371794 | pmc = 24257 | doi = 10.1073/pnas.94.24.13028 | doi-access = free | bibcode = 1997PNAS...9413028F }}</ref>
[[File:The-origins-of-mitochondrion-related-organelles-A-hypothetical-scenario-for-the.png|thumb|Evolution of MROs]]
A few groups of unicellular eukaryotes have only vestigial mitochondria or derived structures: The [[microsporidia]]ns, [[metamonad]]s, and [[archamoebae]].<ref name="Cavalier-Smith-1991">{{cite journal | vauthors = Cavalier-Smith T | title = Archamoebae: the ancestral eukaryotes? | journal = Bio Systems | volume = 25 | issue = 1–2 | pages = 25–38 | year = 1991 | pmid = 1854912 | doi = 10.1016/0303-2647(91)90010-I | bibcode = 1991BiSys..25...25C }}</ref> These groups appear as the most primitive eukaryotes on [[phylogenetic trees]] constructed using [[rRNA]] information, which once suggested that they appeared before the origin of mitochondria. However, this is now known to be an artifact of ''[[long-branch attraction]]'': They are derived groups and retain genes or organelles derived from mitochondria (e.&nbsp;g., [[mitosome]]s and [[hydrogenosome]]s).<ref name="Henze-2003"/> Hydrogenosomes, mitosomes, and related organelles as found in some [[loricifera]] (e.&nbsp;g. ''[[Spinoloricus]]'')<ref>{{cite journal | vauthors = Danovaro R, Dell'Anno A, Pusceddu A, Gambi C, Heiner I, Kristensen RM | title = The first metazoa living in permanently anoxic conditions | journal = BMC Biology | volume = 8 | pages = 30 | date = April 2010 | pmid = 20370908 | pmc = 2907586 | doi = 10.1186/1741-7007-8-30 | doi-access = free }}</ref><ref>{{cite news |last1=Coghlan |first1=Andy |title=Zoologger: The mud creature that lives without oxygen |url=https://www.newscientist.com/article/dn18744-zoologger-the-mud-creature-that-lives-without-oxygen/ |work=New Scientist |date=7 April 2010 }}</ref> and [[myxozoa]] (e.&nbsp;g. ''[[Henneguya zschokkei]]'') are together classified as MROs, mitochondrion-related organelles.<ref name="Yahalomi-2020"/><ref name="Shiflett-2010">{{cite journal | vauthors = Shiflett AM, Johnson PJ | title = Mitochondrion-related organelles in eukaryotic protists | journal = Annual Review of Microbiology | volume = 64 | pages = 409–429 | year = 2010 | pmid = 20528687 | pmc = 3208401 | doi = 10.1146/annurev.micro.62.081307.162826 }}</ref>

''[[Monocercomonoides]]'' and other [[oxymonad]]s appear to have lost their mitochondria completely and at least some of the mitochondrial functions seem to be carried out by cytoplasmic proteins now.<ref name="Karnkowska-2016"/><ref>{{cite journal |last1=Karnkowska |first1=Anna |last2=Treitli |first2=Sebastian C |last3=Brzoň |first3=Ondřej |last4=Novák |first4=Lukáš |last5=Vacek |first5=Vojtěch |last6=Soukal |first6=Petr |last7=Barlow |first7=Lael D |last8=Herman |first8=Emily K |last9=Pipaliya |first9=Shweta V |last10=Pánek |first10=Tomáš |last11=Žihala |first11=David |last12=Petrželková |first12=Romana |last13=Butenko |first13=Anzhelika |last14=Eme |first14=Laura |last15=Stairs |first15=Courtney W |last16=Roger |first16=Andrew J |last17=Eliáš |first17=Marek |last18=Dacks |first18=Joel B |last19=Hampl |first19=Vladimír |title=The Oxymonad Genome Displays Canonical Eukaryotic Complexity in the Absence of a Mitochondrion |journal=Molecular Biology and Evolution |date=1 October 2019 |volume=36 |issue=10 |pages=2292–2312 |doi=10.1093/molbev/msz147 |pmid=31387118 |pmc=6759080 }}</ref><ref name="Novák-2023">{{cite journal | vauthors = Novák LV, Treitli SC, Pyrih J, Hałakuc P, Pipaliya SV, Vacek V, Brzoň O, Soukal P, Eme L, Dacks JB, Karnkowska A, Eliáš M, Hampl V | title = Genomics of Preaxostyla Flagellates Illuminates the Path Towards the Loss of Mitochondria | journal = PLOS Genetics | volume = 19 | issue = 12 | pages = e1011050 | date = December 2023 | pmid = 38060519 | pmc = 10703272 | doi = 10.1371/journal.pgen.1011050 | doi-access = free | veditors = Dutcher SK }}</ref>