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== Orixe evolutiva ==
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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 | url = http://www.sciencedirect.com/science/article/pii/S0167488908000384 | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1783 | issue = 7| pages = 1396–1405 | doi=10.1016/j.bbamcr.2008.01.018}}</ref> but it remains controversial. Some categorize death in those organisms as unregulated, by necrosis or incidental 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 | format = PDF | journal = Nature Reviews Microbiology | volume = 11 | issue = 1| pages = 58–66 | doi=10.1038/nrmicro2929}}</ref> ▼
▲TheA occurrencepresenza ofde programmedmorte cellcellar deathprogramada inen [[ protistprotista]]s isé possibleposible,<ref>{{cite journal | last1 = Deponte | first1 = M | year = 2008 | title = Programmed cell death in protists | url = http://www.sciencedirect.com/science/article/pii/S0167488908000384 | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1783 | issue = 7| pages = 1396–1405 | doi=10.1016/j.bbamcr.2008.01.018}}</ref> butpero itpsegue remainssendo controversialalgo moi discutido. SomeAlgúns categorizecaracterizan death ina thosemorte organismsneses asorganismos unregulatedcomo non regulada, bycomo necrosisunha ornecrose incidentalou deathmorte accidental.<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 | format = PDF | journal = Nature Reviews Microbiology | volume = 11 | issue = 1| pages = 58–66 | doi=10.1038/nrmicro2929}}</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|authorlink=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}}</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.
Considérase que as [[mitocondria]]s se orixinaron a partir de [[bacteria]]s por [[en dosimbiose]] en células eucariotas máis grandes, como propuxo [[Lynn Margulis]] en 1967.<ref>{{cite journal|author=de Duve C|authorlink=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}}</ref> Este paso evolutivo puido ser un risco para as primitivas células eucariotas, que empezaron a fagocitar estar bacterias con [[cadea de transporte de electróns]] produtoras de enerxía, e tamén un perigo para os antepasados das mitocondrias.<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}}</ref>
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.
OneAs ofcélulas theseeucariotas rarecon evolutionarymitocondrias events,viven abouten [[Timelineequilibrio ofentre evolution|twoa billionvida years]] beforee thea presentmorte, madeporque itas possiblemitocondrias foraínda certainreteñen eukaryotesos andseus energy-producingrepertorios prokaryotesde tomoléculas, coexistque andpoden mutuallydesencadear benefito fromsuicidio their [[symbiosis]]celular.<ref>{{cite journal|vauthors=DyallChiarugi SDA, BrownMoskowitz MT, Johnson PJMA |year=20042002|title=AncientCell invasions:biology. fromPARP-1--a endosymbiontsperpetrator toof apoptotic cell organellesdeath?|journal=[[Science (journal)|Science]]|volume=304297|issue=56685579|pages=253–7200–1|pmid=15073369 12114611|doi=10.1126/science.10948841074592}}</ref> Este proceso evolucionou para que ocorra só cando está programada. Cando aparecen certos sinais celulares (como os que proceden de células veciñas, estreses ou [[danos no ADN]]), as mitocondrias liberan activadores das [[caspase]]s que desencadean a fervenza bioquímica indutora da morte celular.
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}}</ref> This process has now been evolved to happen only when programmed.{{Citation needed|date=April 2008}} Given certain [[Cell signaling|signals]] 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.
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== Importancia clínica ==
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