Array ( [0] => {{Short description|Unicellular organism lacking a membrane-bound nucleus}} [1] => [[File:Prokaryote cell.svg|thumb|upright=1.4| Diagram of a typical prokaryotic cell]] [2] => A '''prokaryote''' ({{IPAc-en|p|ɹ|oʊ|ˈ|k|ær|i|oʊ|t|,_|-|ə|t}}, also spelled '''procaryote'''){{Cite web |title=Definition of PROCARYOTE |url=https://www.merriam-webster.com/dictionary/procaryote |access-date=2023-12-30 |website=www.merriam-webster.com |language=en}} is a [[single-cell organism]] whose [[cell (biology)|cell]] lacks a [[cell nucleus|nucleus]] and other [[biological membrane|membrane]]-bound [[organelle]]s.{{cite web|url=http://www.ncsu.edu/project/bio183de/Black/prokaryote/prokaryote1.html|title=Prokaryotes: Single-celled Organisms|author=[[NC State University]]}} The word ''prokaryote'' comes from the [[Ancient Greek]] [[wikt:πρό#Ancient Greek|πρό]] ({{transl|grc|pró}}) 'before' and [[wikt:κάρυον#Ancient Greek|κάρυον]] ({{transl|grc|káruon}}) 'nut, kernel'.Campbell, N. "Biology:Concepts & Connections". Pearson Education. San Francisco: 2003.{{cite web|url=http://www.etymonline.com/index.php?term=prokaryote&allowed_in_frame=0|title=prokaryote|publisher=[[Online Etymology Dictionary]]}} In the [[two-empire system]] arising from the work of [[Édouard Chatton]], prokaryotes were classified within the empire '''Prokaryota'''.{{Cite journal |last1=Sapp |first1=J. |author1-link=Jan Sapp |title=The Prokaryote-Eukaryote Dichotomy: Meanings and Mythology |doi=10.1128/MMBR.69.2.292-305.2005 |journal=[[Microbiology and Molecular Biology Reviews]] |volume=69 |issue=2 |pages=292–305 |year=2005 |pmid=15944457 |pmc=1197417}} But in the [[three-domain system]], based upon [[Molecular phylogenetics|molecular analysis]], prokaryotes are divided into two [[domain (biology)|domains]]: ''[[Bacteria]]'' (formerly Eubacteria) and ''[[Archaea]]'' (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, [[Eukaryote|Eukaryota]].{{cite journal |last1=Coté |first1=Gary |last2=De Tullio |first2=Mario |name-list-style=vanc |date=2010 |title=Beyond Prokaryotes and Eukaryotes: Planctomycetes and Cell Organization |url=http://www.nature.com/scitable/topicpage/beyond-prokaryotes-and-eukaryotes-planctomycetes-and-cell-14158971 |journal=[[Nature (journal)|Nature]]}} [3] => [4] => Prokaryotes [[evolution|evolved]] before eukaryotes, and lack nuclei, [[mitochondria]] or most of the other distinct [[organelle]]s that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components were unenclosed within the [[cytoplasm]] except for an outer [[cell membrane]], but [[bacterial microcompartment]]s, which are thought to be quasi-organelles enclosed in [[protein]] shells (such as the [[encapsulin nanocompartment|encapsulin protein cage]]s), have been discovered,{{cite journal |vauthors=Kerfeld CA, Sawaya MR, Tanaka S, Nguyen CV, Phillips M, Beeby M, Yeates TO |title=Protein structures forming the shell of primitive bacterial organelles |journal=[[Science (journal)|Science]] |volume=309 |issue=5736 |pages=936–8 |date=August 2005 |pmid=16081736 |doi=10.1126/science.1113397 |bibcode=2005Sci...309..936K |citeseerx=10.1.1.1026.896 |s2cid=24561197}}{{cite journal |vauthors=Murat D, Byrne M, Komeili A |title=Cell biology of prokaryotic organelles |journal=Cold Spring Harbor Perspectives in Biology |volume=2 |issue=10 |pages=a000422 |date=October 2010 |pmid=20739411 |pmc=2944366 |doi=10.1101/cshperspect.a000422}} along with other [[Organelle#Prokaryotic organelles|prokaryotic organelles]].{{Cite journal |last1=Murat |first1=Dorothee |last2=Byrne |first2=Meghan |last3=Komeili |first3=Arash |date=2010-10-01 |title=Cell Biology of Prokaryotic Organelles |journal=Cold Spring Harbor Perspectives in Biology |volume=2 |issue=10 |pages=a000422 |doi=10.1101/cshperspect.a000422 |pmc=2944366 |pmid=20739411}} While being unicellular, some prokaryotes, such as [[cyanobacteria]], may form [[colony (biology)|colonies]] held together by [[biofilm]]s, and large colonies can create multilayered [[microbial mat]]s. Others, such as [[myxobacteria]], have multicellular stages in their [[Biological life cycle|life cycles]].{{cite journal |vauthors=Kaiser D |title=Coupling cell movement to multicellular development in myxobacteria |journal=Nature Reviews. Microbiology |volume=1 |issue=1 |pages=45–54 |date=October 2003 |pmid=15040179 |doi=10.1038/nrmicro733 |s2cid=9486133}} Prokaryotes are [[asexual reproduction|asexual]], reproducing via [[Fission (biology)|binary fission]] without any fusion of [[gametes]], although [[horizontal gene transfer]] may take place. [5] => [6] => [[Molecular evolution|Molecular studies]] have provided insight into the evolution and interrelationships of the three domains of life.{{cite journal |vauthors=Sung KH, Song HK |title=Insights into the molecular evolution of HslU ATPase through biochemical and mutational analyses |journal=[[PLOS ONE]] |volume=9 |issue=7 |pages=e103027 |date=July 22, 2014 |pmid=25050622 |pmc=4106860 |doi=10.1371/journal.pone.0103027 |bibcode=2014PLoSO...9j3027S |doi-access=free}} The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization; only eukaryotic cells have an enveloped nucleus that contains its chromosomal [[DNA]], and other characteristic membrane-bound organelles including mitochondria. Distinctive types of prokaryotes include [[extremophile]]s and [[methanogen]]s; these are common in some extreme environments. [7] => [8] => == History == [9] => The distinction between prokaryotes and eukaryotes was firmly established by the microbiologists [[Roger Stanier]] and [[C. B. van Niel]] in their 1962 paper ''The concept of a bacterium''{{cite journal |vauthors=Stanier RY, Van Niel CB |title=The concept of a bacterium |journal=[[Archiv für Mikrobiologie]] |volume=42 |pages=17–35 |year=1962 |issue=1 |pmid=13916221 |doi=10.1007/BF00425185 |s2cid=29859498 |author1-link=Roger Stanier |author2-link=C. B. van Niel}} (though spelled procaryote and eucaryote there). That paper cites [[Édouard Chatton]]'s 1937 book ''Titres et Travaux Scientifiques''{{cite book |last1=Chatton |first1=Édouard |name-list-style=vanc |title=Titres Et Travaux Scientifiques (1906-1937) De Edouard Chatton |date=1937 |publisher=Impr. E. Sottano. |location=Sète}} for using those terms and recognizing the distinction. One reason for this classification was so that what was then often called '''blue-green algae''' (now called [[cyanobacteria]]) would not be classified as plants but grouped with bacteria. [10] => [11] => == Structure == [12] => {{See|Bacterial cell structure|Archaea#Structure, composition development, and operation}} [13] => Prokaryotes have a [[prokaryotic cytoskeleton]] that is more primitive than that of the eukaryotes. Besides [[Homology (biology)|homologues]] of actin and tubulin ([[MreB]] and [[FtsZ]]), the helically arranged building-block of the [[flagellum]], [[flagellin]], is one of the most significant cytoskeletal proteins of bacteria, as it provides structural backgrounds of [[chemotaxis]], the basic cell physiological response of bacteria. At least some prokaryotes also contain intracellular structures that can be seen as primitive organelles. [14] => [15] => Membranous organelles (or intracellular membranes) are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, such as [[photosynthesis]] or [[chemolithotrophy]]. In addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles (e.g. [[carboxysome]]s or gas vacuoles). [16] => [17] => Most prokaryotes are between 1 µm and 10 µm, but they can vary in size from 0.2 µm (''[[Mycoplasma genitalium]]'') to 750 µm (''[[Thiomargarita namibiensis]]''). [18] => [19] => {| class="wikitable" [20] => |- [21] => ! Prokaryotic cell structure [22] => ! Description [23] => |- [24] => | [[Flagellum]] (not always present) [25] => | Long, whip-like protrusion that aids cellular locomotion used by both [[Gram-positive bacteria|gram-positive]] and [[gram-negative bacteria]]. [26] => |- [27] => | [[Cell membrane]] [28] => | Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell. [29] => |- [30] => | [[Cell wall]] (except genera ''[[Mycoplasma]]'' and ''[[Thermoplasma]]'') [31] => | Outer covering of most cells that protects the bacterial cell and gives it shape. [32] => |- [33] => | [[Cytoplasm]] [34] => | A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules. [35] => |- [36] => | [[Ribosome]] [37] => | Cell structures responsible for protein production. [38] => |- [39] => | [[Nucleoid]] [40] => | Area of the cytoplasm that contains the prokaryote's single DNA molecule. [41] => |- [42] => | [[Glycocalyx]] (only in some types of prokaryotes) [43] => | A [[glycoprotein]]-[[polysaccharide]] covering that surrounds the cell membranes. [44] => |- [45] => | [[Cytoplasmic inclusion]]s [46] => | The [[Inclusion (cell)|inclusions]] such as [[ribosome]]s and larger masses scattered in the cytoplasmic matrix. [47] => |} [48] => [49] => == Morphology == [50] => Prokaryotic cells have various shapes; the four basic shapes of bacteria are:{{cite book |vauthors=Bauman RW, Tizard IR, Machunis-Masouka E |title=Microbiology |publisher=Pearson Benjamin Cummings |location=San Francisco |date=2006 |isbn=978-0-8053-7693-7 |url-access=registration |url=https://archive.org/details/microbiology00robe_yj2 }} [51] => * [[Cocci]] – A bacterium that is spherical or ovoid is called a coccus (Plural, cocci). e.g. ''Streptococcus, Staphylococcus.'' [52] => * [[bacillus (shape)|Bacilli]] – A bacterium with cylindrical shape called rod or a bacillus (Plural, bacilli). [53] => * [[Spiral bacteria]] – Some rods twist into spiral shapes and are called spirilla (singular, spirillum). [54] => * [[Vibrio]] – comma-shaped [55] => [56] => The archaeon [[Haloquadratum]] has flat square-shaped cells.{{cite journal |vauthors=Stoeckenius W |title=Walsby's square bacterium: fine structure of an orthogonal procaryote |journal=[[Journal of Bacteriology]] |volume=148 |issue=1 |pages=352–60 |date=October 1981 |pmid=7287626 |pmc=216199 |doi=10.1128/JB.148.1.352-360.1981}} [57] => [58] => == Reproduction == [59] => Bacteria and archaea reproduce through asexual reproduction, usually by [[binary fission]]. Genetic exchange and recombination still occur, but this is a form of [[horizontal gene transfer]] and is not a replicative process, simply involving the transference of DNA between two cells, as in [[bacterial conjugation]]. [60] => [61] => == DNA transfer == [62] => DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has been mainly studied in bacteria. In bacteria, gene transfer occurs by three processes. These are (1) bacterial virus ([[bacteriophage]])-mediated [[Transduction (genetics)|transduction]], (2) [[plasmid]]-mediated [[Bacterial conjugation|conjugation]], and (3) [[Transformation (genetics)|natural transformation]]. Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of [[virus]] particles, rather than an [[adaptation]] of the host bacteria. The transfer of bacterial DNA is under the control of the bacteriophage's genes rather than bacterial genes. Conjugation in the well-studied ''[[Escherichia coli|E. coli]]'' system is controlled by plasmid genes, and is an adaptation for distributing copies of a plasmid from one bacterial host to another. Infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA (conjugation) also appears to be an accidental process rather than a bacterial adaptation. [63] => [[File:Célula Procariota.ogv|thumb|left|250px|3D animation of a prokaryotic cell that shows all the elements that it is composed of]] [64] => Natural bacterial [[Transformation (genetics)|transformation]] involves the transfer of DNA from one bacterium to another through the intervening medium. Unlike transduction and conjugation, transformation is clearly a bacterial [[adaptation]] for DNA transfer, because it depends on numerous bacterial gene products that specifically interact to perform this complex process.{{cite journal |vauthors=Chen I, Dubnau D |title=DNA uptake during bacterial transformation |journal=Nature Reviews. Microbiology |volume=2 |issue=3 |pages=241–9 |date=March 2004 |pmid=15083159 |doi=10.1038/nrmicro844 |s2cid=205499369}} For a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called [[Natural competence|competence]]. About 40 genes are required in ''Bacillus subtilis'' for the development of competence.{{cite journal |vauthors=Solomon JM, Grossman AD |title=Who's competent and when: regulation of natural genetic competence in bacteria |journal=[[Trends in Genetics]] |volume=12 |issue=4 |pages=150–5 |date=April 1996 |pmid=8901420 |doi=10.1016/0168-9525(96)10014-7 }} The length of DNA transferred during ''B. subtilis'' transformation can be as much as a third to the whole chromosome.{{cite journal |vauthors=Akamatsu T, Taguchi H |title=Incorporation of the whole chromosomal DNA in protoplast lysates into competent cells of Bacillus subtilis |journal=[[Bioscience, Biotechnology, and Biochemistry]] |volume=65 |issue=4 |pages=823–9 |date=April 2001 |pmid=11388459 |doi=10.1271/bbb.65.823 |s2cid=30118947|doi-access=free }}{{cite journal |vauthors=Saito Y, Taguchi H, Akamatsu T |title=Fate of transforming bacterial genome following incorporation into competent cells of Bacillus subtilis: a continuous length of incorporated DNA |journal=[[Journal of Bioscience and Bioengineering]] |volume=101 |issue=3 |pages=257–62 |date=March 2006 |pmid=16716928 |doi=10.1263/jbb.101.257}} Transformation is a common mode of DNA transfer, and 67 prokaryotic species are thus far known to be naturally competent for transformation.{{cite journal |vauthors=Johnsborg O, Eldholm V, Håvarstein LS |title=Natural genetic transformation: prevalence, mechanisms and function |journal=[[Research in Microbiology]] |volume =158 |issue=10 |pages=767–78 |date=December 2007 |pmid=17997281 |doi=10.1016/j.resmic.2007.09.004|doi-access=free }} [65] => [66] => Among archaea, ''[[Halobacterium]] volcanii'' forms cytoplasmic bridges between cells that appear to be used for transfer of DNA from one cell to another.{{cite journal |vauthors=Rosenshine I, Tchelet R, Mevarech M |title=The mechanism of DNA transfer in the mating system of an archaebacterium |journal=[[Science (journal)|Science]] |volume=245 |issue=4924 |pages=1387–9 |date=September 1989 |pmid=2818746 |doi=10.1126/science.2818746 |bibcode=1989Sci...245.1387R}} Another archaeon, ''[[Sulfolobus solfataricus]]'', transfers DNA between cells by direct contact. Frols et al. (2008) found{{cite journal |vauthors=Fröls S, Ajon M, Wagner M, Teichmann D, Zolghadr B, Folea M, Boekema EJ, Driessen AJ, Schleper C, Albers SV |title=UV-inducible cellular aggregation of the hyperthermophilic archaeon Sulfolobus solfataricus is mediated by pili formation |journal=[[Molecular Microbiology]] |volume=70 |issue=4 |pages=938–52 |date=November 2008 |pmid=18990182 |doi=10.1111/j.1365-2958.2008.06459.x |s2cid =12797510 |url=https://www.rug.nl/research/portal/files/56956856/UV_inducible_cellular_aggregation_of_the_hyperthermophilic_archaeon_Sulfolobus_solfataricus_is_mediated_by_pili_formation.pdf |doi-access=free}} that exposure of ''S. solfataricus'' to DNA damaging agents induces cellular aggregation, and suggested that cellular aggregation may enhance DNA transfer among cells to provide increased repair of damaged DNA via homologous recombination. [67] => [68] => == Sociality == [69] => While prokaryotes are considered strictly unicellular, most can form stable aggregate communities.{{cite book |edition=13th |publisher=Benjamin Cummings |isbn=9780321649638 |vauthors=Madigan T |title=Brock biology of microorganisms |location=San Francisco |date=2012}} When such communities are encased in a stabilizing polymer matrix ("slime"), they may be called "[[biofilms]]".{{cite book |doi=10.1007/978-3-540-68022-2_2 |chapter=Direct Observations |title=The Biofilm Primer |series=Springer Series on Biofilms |volume=1 |pages=3–4 |year=2007 |isbn=978-3-540-68021-5 |last1=Costerton |first1=J. William |publisher=Springer |location=Berlin, Heidelberg |name-list-style=vanc}} Cells in biofilms often show distinct patterns of [[gene expression]] (phenotypic differentiation) in time and space. Also, as with multicellular eukaryotes, these changes in expression often appear to result from [[cell signaling|cell-to-cell signaling]], a phenomenon known as [[quorum sensing]]. [70] => [71] => Biofilms may be highly heterogeneous and structurally complex and may attach to solid surfaces, or exist at liquid-air interfaces, or potentially even liquid-liquid interfaces. Bacterial biofilms are often made up of [[microcolony|microcolonies]] (approximately dome-shaped masses of bacteria and matrix) separated by "voids" through which the medium (e.g., water) may flow easily. The microcolonies may join together above the substratum to form a continuous layer, closing the network of channels separating microcolonies. This structural complexity—combined with observations that oxygen limitation (a ubiquitous challenge for anything growing in size beyond the scale of diffusion) is at least partially eased by movement of medium throughout the biofilm—has led some to speculate that this may constitute a [[circulatory system]]{{cite journal |vauthors=Costerton JW, Lewandowski Z, Caldwell DE, Korber DR, Lappin-Scott HM |title=Microbial biofilms |journal=[[Annual Review of Microbiology]] |volume=49 |pages=711–45 |date=October 1995 |issue=1 |pmid=8561477 |doi=10.1146/annurev.mi.49.100195.003431}} and many researchers have started calling prokaryotic communities multicellular (for example {{cite journal |vauthors=Shapiro JA |title=Thinking about bacterial populations as multicellular organisms |journal=[[Annual Review of Microbiology]] |volume=52 |pages=81–104 |date=1998 |issue=1 |pmid=9891794 |doi=10.1146/annurev.micro.52.1.81 |url=http://www.sci.uidaho.edu/newton/math501/Sp05/Shapiro.pdf |author-link=James A. Shapiro |archive-url=https://web.archive.org/web/20110717183759/http://www.sci.uidaho.edu/newton/math501/Sp05/Shapiro.pdf |url-status=dead |archive-date=2011-07-17 }}). Differential cell expression, collective behavior, signaling, [[programmed cell death]], and (in some cases) discrete [[biological dispersal]]{{cite journal |vauthors=Chua SL, Liu Y, Yam JK, Chen Y, Vejborg RM, Tan BG, Kjelleberg S, Tolker-Nielsen T, Givskov M, Yang L |title=Dispersed cells represent a distinct stage in the transition from bacterial biofilm to planktonic lifestyles |journal=[[Nature Communications]] |volume=5 |pages=4462 |date=July 2014 |issue=1 |pmid=25042103 |doi=10.1038/ncomms5462 |bibcode=2014NatCo...5.4462C |doi-access=free}} events all seem to point in this direction. However, these colonies are seldom if ever founded by a single founder (in the way that animals and plants are founded by single cells), which presents a number of theoretical issues. Most explanations of [[Co-operation (evolution)|co-operation]] and the [[evolution of multicellularity]] have focused on high relatedness between members of a group (or colony, or whole organism). If a copy of a gene is present in all members of a group, behaviors that promote cooperation between members may permit those members to have (on average) greater fitness than a similar group of selfish individuals{{cite journal |vauthors=Hamilton WD |title=The genetical evolution of social behaviour. II |journal=[[Journal of Theoretical Biology]] |volume=7 |issue=1 |pages=17–52 |date=July 1964 |pmid=5875340 |doi=10.1016/0022-5193(64)90039-6 |bibcode=1964JThBi...7...17H}} (see [[inclusive fitness]] and [[Hamilton's rule]]). [72] => [73] => Should these instances of prokaryotic sociality prove to be the rule rather than the exception, it would have serious implications for the way we view prokaryotes in general, and the way we deal with them in medicine.{{cite book |vauthors=Balaban N, Ren D, Givskov M, Rasmussen TB |chapter=Introduction |doi=10.1007/7142_2007_006 |title=Control of Biofilm Infections by Signal Manipulation |series=Springer Series on Biofilms |volume=2 |pages=1–11 |year=2008 |publisher=Springer |location=Berlin, Heidelberg |isbn=978-3-540-73852-7}} Bacterial biofilms may be 100 times more resistant to antibiotics than free-living unicells and may be nearly impossible to remove from surfaces once they have colonized them.{{cite journal |vauthors=Costerton JW, Stewart PS, Greenberg EP |title=Bacterial biofilms: a common cause of persistent infections |journal=[[Science (journal)|Science]] |volume=284 |issue=5418 |pages=1318–22 |date=May 1999 |pmid=10334980 |doi=10.1126/science.284.5418.1318 |bibcode=1999Sci...284.1318C |s2cid=27364291 |url=https://scholarworks.montana.edu/xmlui/handle/1/14368 }} Other aspects of bacterial cooperation—such as [[bacterial conjugation]] and quorum-sensing-mediated [[pathogenicity]], present additional challenges to researchers and medical professionals seeking to treat the associated diseases. [74] => [75] => == Environment == [76] => [[File:Anillo de la vida.png|thumb|upright=1.4|Phylogenetic ring showing the diversity of prokaryotes, and symbiogenetic origins of eukaryotes]] [77] => [78] => Prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types. For example, in addition to using [[photosynthesis]] or [[organic compound]]s for energy, as eukaryotes do, prokaryotes may obtain energy from [[inorganic compound]]s such as [[hydrogen sulfide]]. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of [[Antarctica]], studied in [[cryobiology]], or as hot as undersea [[hydrothermal vent]]s and land-based [[hot spring]]s. [79] => [80] => Prokaryotes live in nearly all environments on Earth. Some archaea and bacteria are [[extremophile]]s, thriving in harsh conditions, such as high temperatures ([[thermophile]]s) or high salinity ([[halophile]]s).{{cite book |vauthors=Hogan CM |date=2010 |chapter-url=http://www.eoearth.org/article/Extremophile?topic=49540 |chapter=Extremophile |title=Encyclopedia of Earth |publisher=National Council of Science & the Environment |veditors=Monosson E, Cleveland C}} Many archaea grow as [[plankton]] in the oceans. [[Symbiotic]] prokaryotes live in or on the bodies of other organisms, including humans. Prokaryote have high populations in the [[soil]] - including the [[rhizosphere]] and [[rhizosheath]]. Soil prokaryotes are still heavily undercharacterized despite their easy proximity to humans and their tremendous [[Agricultural microbiology|economic importance to agriculture]].{{cite journal |last1=Cobián Güemes |first1=Ana Georgina |last2=Youle |first2=Merry |last3=Cantú |first3=Vito Adrian |last4=Felts |first4=Ben |last5=Nulton |first5=James |last6=Rohwer |first6=Forest |title=Viruses as Winners in the Game of Life |journal=[[Annual Review of Virology]] |publisher=[[Annual Reviews (publisher)|Annual Reviews]] |volume=3 |issue=1 |date=2016-09-29 |issn=2327-056X |doi=10.1146/annurev-virology-100114-054952 |pages=197–214 |pmid=27741409 |s2cid=36517589}} [81] => [82] => [[File:Tree of Living Organisms 2.png|thumb|Phylogenetic and [[symbiogenesis|symbiogenetic]] tree of living organisms, showing the origins of [[eukaryote]]s and prokaryotes]] [83] => [84] => == Classification == [85] => In 1977, [[Carl Woese]] proposed dividing prokaryotes into the [[Bacteria]] and [[Archaea]] (originally Eubacteria and Archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms. Archaea were originally thought to be extremophiles, living only in inhospitable conditions such as extremes of [[temperature]], [[pH]], and [[radiation]] but have since been found in all types of [[habitat]]s. The resulting arrangement of Eukaryota (also called "Eucarya"), Bacteria, and Archaea is called the [[three-domain system]], replacing the traditional [[two-empire system]].{{cite journal |vauthors=Woese CR |title=There must be a prokaryote somewhere: microbiology's search for itself |journal=[[Microbiological Reviews]] |volume=58 |issue=1 |pages=1–9 |date=March 1994 |pmid=8177167 |pmc=372949 |doi=10.1128/MMBR.58.1.1-9.1994}}{{cite journal |vauthors=Sapp J |title=The prokaryote-eukaryote dichotomy: meanings and mythology |journal=[[Microbiology and Molecular Biology Reviews]] |volume=69 |issue=2 |pages=292–305 |date=June 2005 |pmid=15944457 |pmc=1197417 |doi=10.1128/MMBR.69.2.292-305.2005}} [86] => [87] => === Phylogenetic tree === [88] => According to the phylogenetic analysis of Hug (2016), the relationships could be the following:{{Cite journal |last=Hug |first=Laura A. |last2=Baker |first2=Brett J. |last3=Anantharaman |first3=Karthik |last4=Brown |first4=Christopher T. |last5=Probst |first5=Alexander J. |last6=Castelle |first6=Cindy J. |last7=Butterfield |first7=Cristina N. |last8=Hernsdorf |first8=Alex W. |last9=Amano |first9=Yuki |last10=Ise |first10=Kotaro |last11=Suzuki |first11=Yohey |last12=Dudek |first12=Natasha |last13=Relman |first13=David A. |last14=Finstad |first14=Kari M. |last15=Amundson |first15=Ronald |date=2016-04-11 |title=A new view of the tree of life |url=https://www.nature.com/articles/nmicrobiol201648 |journal=Nature Microbiology |language=en |volume=1 |issue=5 |pages=1–6 |doi=10.1038/nmicrobiol.2016.48 |issn=2058-5276|doi-access=free }} [89] => [[File:A Novel Representation Of The Tree Of Life.png|thumb|500px|Phylogenetic tree showing the diversity of prokaryote.|center]]{{Clear}} [90] => [91] => == Evolution == [92] => {{anchor|Prokaryogenesis}} [93] => {{Main|Molecular evolution}} [94] => [[File:Primordial biogenesis.svg|thumb|upright=1.25|Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view, one of many on the relative positions of Prokaryotes and Eukaryotes, implies that the universal common ancestor was relatively large and complex.{{cite journal |vauthors=Egel R |title=Primal eukaryogenesis: on the communal nature of precellular States, ancestral to modern life |journal=[[Life (journal)|Life]] |volume=2 |issue=1 |pages=170–212 |date=January 2012 |pmid=25382122 |pmc=4187143 |doi=10.3390/life2010170 |bibcode=2012Life....2..170E |doi-access=free}}]] [95] => [96] => A widespread current model of the evolution of the [[origin of life|first living organisms]] is that these were some form of prokaryotes, which may have evolved out of [[protocell]]s, while the eukaryotes evolved later in the history of life.{{cite journal |vauthors=Zimmer C |title=Origins. On the origin of eukaryotes |journal=[[Science (journal)|Science]] |volume=325 |issue=5941 |pages=666–8 |date=August 2009 |pmid=19661396 |doi=10.1126/science.325_666}} Some authors have questioned this conclusion, arguing that the current set of prokaryotic species may have evolved from more complex eukaryotic ancestors through a process of simplification.{{cite journal |vauthors=Brown JR |title=Ancient horizontal gene transfer |journal=Nature Reviews. Genetics |volume=4 |issue=2 |pages=121–32 |date=February 2003 |pmid=12560809 |doi=10.1038/nrg1000 |s2cid=22294114}}{{cite journal |vauthors=[[Patrick Forterre|Forterre P]], Philippe H |title=Where is the root of the universal tree of life? |journal=[[BioEssays]] |volume=21 |issue=10 |pages=871–9 |date=October 1999 |pmid=10497338 |doi=10.1002/(SICI)1521-1878(199910)21:10<871::AID-BIES10>3.0.CO;2-Q}}{{cite journal |vauthors=Poole A, Jeffares D, Penny D |title=Early evolution: prokaryotes, the new kids on the block |journal=[[BioEssays]] |volume=21 |issue=10 |pages=880–9 |date=October 1999 |pmid=10497339 |doi=10.1002/(SICI)1521-1878(199910)21:10<880::AID-BIES11>3.0.CO;2-P |s2cid=45607498 }} [97] => [98] => Others have argued that the three domains of life arose simultaneously, from a set of varied cells that formed a single gene pool.{{cite journal |vauthors=Woese C |title=The universal ancestor |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=95 |issue=12 |pages=6854–9 |date=June 1998 |pmid=9618502 |pmc=22660 |doi=10.1073/pnas.95.12.6854 |bibcode=1998PNAS...95.6854W |doi-access=free}} This controversy was summarized in 2005:{{cite book |last=Martin |first=William |chapter=Woe is the Tree of Life |title=Microbial Phylogeny and Evolution: Concepts and Controversies |editor-first=Jan |editor-last=Sapp |location=Oxford |publisher=[[Oxford University Press]] |date=2005 |pages=139}} [99] => [100] =>
[101] => There is no consensus among biologists concerning the position of the eukaryotes in the overall scheme of cell evolution. Current opinions on the origin and position of eukaryotes span a broad spectrum including the views that eukaryotes arose first in evolution and that prokaryotes descend from them, that eukaryotes arose contemporaneously with eubacteria and archaebacteria and hence represent a primary line of descent of equal age and rank as the prokaryotes, that eukaryotes arose through a symbiotic event entailing an endosymbiotic origin of the nucleus, that eukaryotes arose without endosymbiosis, and that eukaryotes arose through a symbiotic event entailing a simultaneous endosymbiotic origin of the flagellum and the nucleus, in addition to many other models, which have been reviewed and summarized elsewhere. [102] =>
[103] => [104] => The oldest known [[fossil]]ized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth's crust. Eukaryotes only appear in the fossil record later, and may have formed from [[endosymbiotic theory|endosymbiosis]] of multiple prokaryote ancestors. The oldest known fossil eukaryotes are about 1.7 billion years old. However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago.[[Carl Woese]], [[J Peter Gogarten]], "[http://www.scientificamerican.com/article/when-did-eukaryotic-cells/ When did eukaryotic cells (cells with nuclei and other internal organelles) first evolve? What do we know about how they evolved from earlier life-forms?]" ''[[Scientific American]]'', October 21, 1999. [105] => [106] => While Earth is the only place in the universe where life is known to exist, some have suggested that there is [[Life on Mars (planet)|evidence on Mars]] of fossil or living prokaryotes.{{cite journal |vauthors=McSween HY |title=Evidence for life in a martian meteorite? |journal=GSA Today |volume=7 |issue=7 |pages=1–7 |date=July 1997 |pmid=11541665}}{{cite journal |vauthors=McKay DS, Gibson EK, Thomas-Keprta KL, Vali H, Romanek CS, Clemett SJ, Chillier XD, Maechling CR, Zare RN |title=Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001 |journal=[[Science (journal)|Science]] |volume=273 |issue=5277 |pages=924–30 |date=August 1996 |pmid=8688069 |doi=10.1126/science.273.5277.924 |bibcode=1996Sci...273..924M |s2cid=40690489 }} However, this possibility remains the subject of considerable debate and skepticism.{{cite web |title=After 10 years, few believe life on Mars |url=http://www.space.com/scienceastronomy/ap_060806_mars_rock.html |last=Crenson |first=Matt |name-list-style=vanc |publisher=[[Associated Press]] (on space.com]) |date=2006-08-06 |access-date=2006-08-06 |archive-url=https://web.archive.org/web/20060809161936/http://www.space.com/scienceastronomy/ap_060806_mars_rock.html |archive-date=2006-08-09 |url-status=dead}}{{cite journal |vauthors=Scott ER |title=Origin of carbonate-magnetite-sulfide assemblages in Martian meteorite ALH84001 |journal=[[Journal of Geophysical Research]] |volume=104 |issue=E2 |pages=3803–13 |date=February 1999 |pmid=11542931 |doi=10.1029/1998JE900034 |bibcode=1999JGR...104.3803S |doi-access=free}} [107] => [108] => == Relationship to eukaryotes == [109] => [[Image:Celltypes.svg|thumb|left|upright=1.4|Comparison of eukaryotes vs. prokaryotes]] [110] => The division between prokaryotes and eukaryotes is usually considered the most important distinction or difference among organisms. The distinction is that eukaryotic cells have a "true" [[cell nucleus|nucleus]] containing their [[DNA]], whereas prokaryotic cells do not have a nucleus. [111] => [112] => Both eukaryotes and prokaryotes contain large [[RNA]]/[[protein]] structures called [[ribosome]]s, which [[Translation (biology)|produce protein]], but the [[ribosomes]] of prokaryotes are smaller than those of eukaryotes. [[Mitochondria]] and [[chloroplast]]s, two organelles found in many eukaryotic cells, contain ribosomes similar in size and makeup to those found in prokaryotes.{{cite book |title=The Molecular Biology of the Cell |url=https://archive.org/details/molecularbiolog000wils |url-access=registration |edition=fourth |author=Bruce Alberts |display-authors=etal |publisher=Garland Science |date=2002 |pages=808 |isbn=0-8153-3218-1 }} This is one of many pieces of evidence that mitochondria and chloroplasts are descended from free-living bacteria. The [[endosymbiotic theory]] holds that early eukaryotic cells took in primitive prokaryotic cells by [[phagocytosis]] and adapted themselves to incorporate their structures, leading to the mitochondria and chloroplasts. [113] => [114] => The [[genome]] in a prokaryote is held within a DNA/protein complex in the [[cytosol]] called the [[nucleoid]], which lacks a [[nuclear envelope]].{{cite journal |vauthors=Thanbichler M, Wang SC, Shapiro L |title=The bacterial nucleoid: a highly organized and dynamic structure |journal=[[Journal of Cellular Biochemistry]] |volume=96 |issue=3 |pages=506–21 |date=October 2005 |pmid=15988757 |doi=10.1002/jcb.20519 |s2cid=25355087 |doi-access=free}} The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized [[chromosome]]s found in eukaryotic cells. In addition, many important genes of prokaryotes are stored in separate circular DNA structures called [[plasmid]]s. Like Eukaryotes, prokaryotes may partially duplicate genetic material, and can have a [[haploid]] chromosomal composition that is partially replicated, a condition known as [[merodiploid]]y.{{cite journal |vauthors=Johnston C, Caymaris S, Zomer A, Bootsma HJ, Prudhomme M, Granadel C, Hermans PW, Polard P, Martin B, Claverys JP |title=Natural genetic transformation generates a population of merodiploids in Streptococcus pneumoniae |journal=[[PLOS Genetics]] |volume=9 |issue=9 |pages=e1003819 |date=2013 |pmid=24086154 |pmc=3784515 |doi=10.1371/journal.pgen.1003819 |doi-access=free }} [115] => [116] => Prokaryotes lack [[mitochondrion|mitochondria]] and [[chloroplast]]s. Instead, processes such as [[oxidative phosphorylation]] and [[photosynthesis]] take place across the prokaryotic [[cell membrane]].{{cite journal |vauthors=Harold FM |title=Conservation and transformation of energy by bacterial membranes |journal=[[Bacteriological Reviews]] |volume=36 |issue=2 |pages=172–230 |date=June 1972 |pmid=4261111 |pmc=408323 |doi=10.1128/MMBR.36.2.172-230.1972 }} However, prokaryotes do possess some internal structures, such as [[prokaryotic cytoskeleton]]s.{{cite journal |vauthors=Shih YL, Rothfield L |title=The bacterial cytoskeleton |journal=[[Microbiology and Molecular Biology Reviews]] |volume=70 |issue=3 |pages=729–54 |date=September 2006 |pmid=16959967 |pmc=1594594 |doi=10.1128/MMBR.00017-06}}{{cite journal |vauthors=Michie KA, Löwe J |title=Dynamic filaments of the bacterial cytoskeleton |journal=[[Annual Review of Biochemistry]] |volume=75 |pages=467–92 |date=2006 |issue=1 |pmid=16756499 |doi=10.1146/annurev.biochem.75.103004.142452 |url=http://www2.mrc-lmb.cam.ac.uk/SS/Lowe_J/group/PDF/annrev2006.pdf |archive-url=https://web.archive.org/web/20061117183040/http://www2.mrc-lmb.cam.ac.uk/SS/Lowe_J/group/PDF/annrev2006.pdf |url-status=dead |archive-date=November 17, 2006}} It has been suggested that the bacterial phylum [[Planctomycetota]] has a membrane around the nucleoid and contains other membrane-bound cellular structures.{{cite journal |vauthors=Fuerst JA |title=Intracellular compartmentation in planctomycetes |journal=[[Annual Review of Microbiology]] |volume=59 |pages=299–328 |date=2005 |issue=1 |pmid=15910279 |doi=10.1146/annurev.micro.59.030804.121258 }} However, further investigation revealed that Planctomycetota cells are not compartmentalized or nucleated and, like other bacterial membrane systems, are interconnected.{{cite journal |vauthors=Santarella-Mellwig R, Pruggnaller S, Roos N, Mattaj IW, Devos DP |title=Three-dimensional reconstruction of bacteria with a complex endomembrane system |journal=[[PLOS Biology]] |volume=11 |issue=5 |pages=e1001565 |date=2013 |pmid=23700385 |pmc=3660258 |doi=10.1371/journal.pbio.1001565 |doi-access=free }} [117] => [118] => Prokaryotic cells are usually much smaller than eukaryotic cells. Therefore, prokaryotes have a larger [[surface-area-to-volume ratio]], giving them a higher [[metabolic rate]], a higher growth rate, and as a consequence, a shorter generation time than eukaryotes. [119] => [120] => [[File:Phylogenetic Tree of Prokaryota.png|thumb|upright=2.5|Phylogenetic tree showing the diversity of prokaryotes.{{cite journal |vauthors=Castelle CJ, Banfield JF |title=Major New Microbial Groups Expand Diversity and Alter our Understanding of the Tree of Life |journal=[[Cell (journal)|Cell]] |volume=172 |issue=6 |pages=1181–1197 |date= March 2018 |pmid=29522741 |doi=10.1016/j.cell.2018.02.016 |url=http://www.escholarship.org/uc/item/0299z0z4 |doi-access=free}} [121] => This 2018 proposal shows eukaryotes emerging from the archaean [[Asgard (archaea)|Asgard]] group which represents a modern version of the [[eocyte hypothesis]]. Unlike earlier assumptions, the division between bacteria and the rest is the most important difference between organisms.]] [122] => [123] => There is increasing evidence that the roots of the eukaryotes are to be found in (or at least next to) the archaean [[Asgard (archaea)|asgard]] group, perhaps [[Heimdallarchaeota]] (an idea which is a modern version of the 1984 [[eocyte hypothesis]], ''eocytes'' being an old synonym for ''[[Thermoproteota]]'', a [[taxon]] to be found nearby the then-unknown Asgard group). For example, [[Histone#Conservation across species|histones]] which usually package DNA in eukaryotic nuclei, have also been found in several archaean groups, giving evidence for [[Homology (biology)|homology]]. This idea might clarify the mysterious predecessor of eukaryotic cells ([[Eukaryote#Cell features|eucytes]]) which engulfed an [[alphaproteobacteria|alphaproteobacterium]] forming the first eucyte ([[Eukaryote#Origin of eukaryotes|LECA]], '''l'''ast '''e'''ukaryotic '''c'''ommon '''a'''ncestor) according to [[endosymbiotic theory]]. There might have been some additional support by viruses, called [[viral eukaryogenesis]]. [124] => The non-bacterial group comprising archaea and eukaryota was called [[Neomura]] by [[Thomas Cavalier-Smith]] in 2002.{{cite journal |author=Cavalier-Smith T |title=The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa |journal=Int. J. Syst. Evol. Microbiol. |volume=52 |issue=Pt 2 |pages=297–354 |date=March 2002 |pmid=11931142 |doi=10.1099/00207713-52-2-297 |url=http://ijs.sgmjournals.org/cgi/pmidlookup?view=long&pmid=11931142}} [125] => However, in a [[Clade|cladistic]] view, eukaryota ''are'' archaea in the same sense as [[birds]] ''are'' [[dinosaurs]] because they evolved from the [[maniraptora]] dinosaur group. In contrast, archaea ''without'' eukaryota appear to be a [[paraphyletic]] group, just like dinosaurs without birds. [126] => [127] => == Prokaryotes may be split into two groups == [128] => Unlike the above assumption of a fundamental split between prokaryotes and eukaryotes, the most important difference between [[Biota (taxonomy)|biota]] may be the division between bacteria and the rest (archaea and eukaryota). For instance, [[DNA replication]] differs fundamentally between bacteria and archaea (including that in eukaryotic nuclei), and it may not be homologous between these two groups.{{cite journal |vauthors=Barry ER, Bell SD |title=DNA replication in the archaea |journal=[[Microbiology and Molecular Biology Reviews]] |volume=70 |issue=4 |pages=876–87 |date=December 2006 |pmid=17158702 |pmc=1698513 |doi=10.1128/MMBR.00029-06}} Moreover, [[ATP synthase]], though common (homologous) in all organisms, differs greatly between bacteria (including eukaryotic [[organelle]]s such as [[mitochondrion|mitochondria]] and [[chloroplast]]s) and the archaea/eukaryote nucleus group. The last common antecessor of all life (called [[LUCA#Location of the root|LUCA]], '''l'''ast '''u'''niversal '''c'''ommon '''a'''ncestor) should have possessed an early version of this protein complex. As ATP synthase is obligate membrane bound, this supports the assumption that LUCA was a cellular organism. The [[RNA world hypothesis]] might clarify this scenario, as LUCA might have been a [[ribosome#Origin|ribocyte]] (also called ribocell) lacking DNA, but with an [[RNA]] genome built by [[ribosome]]s as [[Woese's dogma#Ribosomes as primordial self-replicating entities|primordial self-replicating entities]].{{cite book |vauthors=Lane N |author-link1 = Nick Lane |url=https://archive.org/details/vitalquestionene0000lane |url-access=registration |page=[https://archive.org/details/vitalquestionene0000lane/page/77 77] |title=The Vital Question – Energy, Evolution, and the Origins of Complex Life |publisher=[[W. W. Norton]] |date=2015 |isbn=978-0-393-08881-6}} A [[Peptide-RNA world]] (also called [[Nucleoprotein#Ribonucleoproteins|RNP]] world) hypothesis has been proposed based on the idea that [[oligopeptide]]s may have been built together with primordial nucleic acids at the same time, which also supports the concept of a [[ribocyte]] as LUCA. The feature of DNA as the material base of the genome might have then been adopted separately in bacteria and in archaea (and later eukaryote nuclei), presumably by help of some viruses (possibly [[retroviruses]] as they could [[reverse transcription|reverse transcribe]] RNA to DNA).{{cite journal |doi=10.1073/pnas.0510333103 |last1=Forterre |first1=Patrick |name-list-style=vanc |year=2006 |title=Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: A hypothesis for the origin of cellular domain |journal=[[PNAS]] |volume=103 |issue=10 |pages=3669–3674 |pmid=16505372 |pmc=1450140 |bibcode=2006PNAS..103.3669F |doi-access=free}} As a result, prokaryota comprising bacteria and archaea may also be [[polyphyletic]]. [129] => [130] => == See also == [131] => {{Portal|Biology}} [132] => {{columns-list|colwidth=30em| [133] => * [[Actinonin]] [134] => * [[Bacterial cell structure]] [135] => * [[Combrex]] [136] => * [[Evolution of cells]] [137] => * [[Evolution of sexual reproduction]] [138] => * [[List of sequenced archaeal genomes]] [139] => * [[List of sequenced bacterial genomes]] [140] => * [[Marine prokaryotes]] [141] => * [[Monera]], an obsolete [[kingdom (biology)|kingdom]] including [[Archaea]] and [[Bacteria]] [142] => * [[Nanobacterium]] [143] => * [[Nanobe]] [144] => * ''[[Parakaryon myojinensis]]'' [145] => * [[ProGlycProt]] [146] => }} [147] => [148] => == References == [149] => {{Reflist|32em}} [150] => [151] => == External links == [152] => {{Commons category|Procaryota}} [153] => * [http://wiki.biomine.skelleftea.se/wiki/index.php/Prokaryote_versus_eukaryote Prokaryote versus eukaryote, BioMineWiki] {{Webarchive|url=https://web.archive.org/web/20121025065711/http://wiki.biomine.skelleftea.se/wiki/index.php/Prokaryote_versus_eukaryote |date=2012-10-25 }} [154] => * [https://web.archive.org/web/20130502073028/http://www.taxonomicoutline.org/ The Taxonomic Outline of Bacteria and Archaea] [155] => * [http://mmbr.asm.org/content/69/2/292.full The Prokaryote-Eukaryote Dichotomy: Meanings and Mythology] [156] => * [http://www.thatquiz.org/tq/practice.html?cells_imgmap Quiz on prokaryote anatomy] [157] => * [http://tolweb.org/Life_on_Earth/1 TOLWEB page on Eukaryote-Prokaryote phylogeny] [158] => [159] => {{NCBI-scienceprimer}} [160] => {{Bacteria classification|state=collapsed}} [161] => {{Archaea classification|state=collapsed}} [162] => {{Bacteria}} [163] => {{Authority control}} [164] => [165] => [[Category:Prokaryotes| ]] [166] => [[Category:Bacteriology]] [167] => [[Category:Biochemistry]] [168] => [[Category:Paraphyletic groups]] [169] => [[Category:Articles containing video clips]] [] => )
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Prokaryote

A prokaryote is a type of cell that lacks a nucleus and other membrane-bound organelles. It is one of the two broad classifications of living organisms, the other being eukaryotes.

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It is one of the two broad classifications of living organisms, the other being eukaryotes. Prokaryotes are found in various habitats and include organisms such as bacteria and archaea. On the Wikipedia page for prokaryote, readers can find detailed information about the characteristics, structure, and classification of prokaryotic cells. The page provides an overview of their genetic material, which is organized in a single circular chromosome and often contains plasmids. It also describes the absence of a nucleus, explaining how prokaryotes have a simpler internal structure compared to eukaryotes. The page delves into the diverse metabolic capabilities of prokaryotes, including photosynthesis, chemosynthesis, and fermentation. It highlights their role in various ecological processes such as nutrient cycling and symbiotic relationships. Additionally, the page discusses the important practical applications of prokaryotes in fields such as biotechnology and medicine. Furthermore, readers will find information about the evolutionary history and classification of prokaryotes, with sections dedicated to bacteria and archaea. The page outlines the major differences between these two groups and provides examples of their respective phyla and species. It also highlights the importance of studying prokaryotes for understanding the origins and diversity of life on Earth. In addition to scientific information, the page discusses the medical significance of prokaryotes, including their role as pathogens and the development of antibiotic resistance. It also covers the impact of prokaryotes on the environment, including their involvement in carbon and nitrogen cycles, as well as their potential as bioremediation agents. Overall, the Wikipedia page on prokaryotes provides a comprehensive overview of these organisms, covering various aspects of their biology, ecology, and significance in scientific research and everyday life.

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