Editing Programmed cell death (section)

==Evolutionary origin of mitochondrial apoptosis==
{{Further|Symbiogenesis}}
The occurrence of programmed cell death in [[protist]]s is possible,<ref>{{cite journal | last1 = Deponte | first1 = M | year = 2008 | title = Programmed cell death in protists | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1783 | issue = 7| pages = 1396–1405 | doi=10.1016/j.bbamcr.2008.01.018| pmid = 18291111 | doi-access = free }}</ref><ref>Kaczanowski S, Sajid M and Reece S E 2011 Evolution of apoptosis-like programmed cell death in unicellular protozoan parasites Parasites Vectors 4 44</ref> but it remains controversial. Some categorize death in those organisms as unregulated apoptosis-like cell death.<ref>{{cite journal | last1 = Proto | first1 = W. R. | last2 = Coombs | first2 = G. H. | last3 = Mottram | first3 = J. C. | year = 2012 | title = Cell death in parasitic protozoa: regulated or incidental? | url = http://www.gla.ac.uk/media/media_248886_en.pdf | journal = Nature Reviews Microbiology | volume = 11 | issue = 1 | pages = 58–66 | doi = 10.1038/nrmicro2929 | pmid = 23202528 | s2cid = 1633550 | access-date = 2014-11-14 | archive-url = https://web.archive.org/web/20160303235943/http://www.gla.ac.uk/media/media_248886_en.pdf | archive-date = 2016-03-03 | url-status = dead }}</ref><ref>{{cite journal | title=Evolution of apoptosis-like programmed cell death in unicellular protozoan parasites | author=Szymon Kaczanowski | author2=Mohammed Sajid | author3=Sarah E Reece | journal=Parasites & Vectors | year=2011 | volume=4 | pages=44 | doi=10.1186/1756-3305-4-44| pmid=21439063 | pmc=3077326 | doi-access=free }}</ref>

Biologists had long suspected that [[mitochondria]] originated from [[bacteria]] that had been incorporated as [[endosymbiont]]s ("living together inside") of larger eukaryotic cells. It was [[Lynn Margulis]] who from 1967 on championed this [[theory]], which has since become widely accepted.<ref>{{cite journal|author=de Duve C|author-link=Christian de Duve|year=1996|title=The birth of complex cells|journal=[[Scientific American]]|volume=274|issue=4|pages=50–7|pmid=8907651|doi=10.1038/scientificamerican0496-50|bibcode=1996SciAm.274d..50D}}</ref> The most convincing [[evidence]] for this theory is the fact that mitochondria possess their own [[DNA]] and are equipped with [[gene]]s and [[DNA replication|replication]] apparatus.{{cn|date=November 2024}}

This [[evolution]]ary step would have been risky for the primitive eukaryotic cells, which began to engulf the [[Electron transport chain|energy-producing]] bacteria, as well as a perilous step for the ancestors of mitochondria, which began to invade their proto-eukaryotic [[Host (biology)|hosts]]. This process is still evident today, between [[human]] white [[White blood cell|blood cells]] and bacteria. Most of the time, invading bacteria are destroyed by the white blood cells; however, it is not uncommon for the [[chemical warfare]] waged by [[prokaryote]]s to succeed, with the consequence known as [[infection]] by its resulting damage.{{cn|date=November 2024}}

One of these rare evolutionary events, about [[Timeline of evolution|two billion years]] before the present, made it possible for certain eukaryotes and energy-producing prokaryotes to coexist and mutually benefit from their [[symbiosis]].<ref>{{cite journal|vauthors=Dyall SD, Brown MT, Johnson PJ |year=2004|title=Ancient invasions: from endosymbionts to organelles|journal=[[Science (journal)|Science]]|volume=304|issue=5668|pages=253–7|pmid=15073369|doi=10.1126/science.1094884|bibcode=2004Sci...304..253D|s2cid=19424594}}</ref>

Mitochondriate eukaryotic cells live poised between [[life]] and death, because mitochondria still retain their repertoire of [[molecule]]s that can trigger cell suicide.<ref>{{cite journal|vauthors=Chiarugi A, Moskowitz MA |year=2002|title=Cell biology. PARP-1--a perpetrator of apoptotic cell death?|journal=[[Science (journal)|Science]]|volume=297|issue=5579|pages=200–1|pmid= 12114611|doi=10.1126/science.1074592|s2cid=82828773}}</ref> It is not clear why apoptotic machinery is maintained in the extant unicellular organisms. This process has now been evolved to happen only when programmed.<ref>Kaczanowski, S. Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging. Phys Biol 13, http://iopscience.iop.org/article/10.1088/1478-3975/13/3/031001</ref> to cells (such as feedback from neighbors, stress or [[DNA repair|DNA damage]]), mitochondria release [[caspase]] activators that trigger the cell-death-inducing [[Biochemistry|biochemical]] cascade. As such, the cell suicide [[Reaction mechanism|mechanism]] is now crucial to all of our lives.{{cn|date=November 2024}}