Eukaryote 9530 225344103 2008-07-13T05:12:44Z RSkyhawk 5496366 [[WP:UNDO|Undid]] revision 225340875 by [[Special:Contributions/124.106.115.73|124.106.115.73]] ([[User talk:124.106.115.73|talk]])-Apparent test edit {{Taxobox | color = #e0d0b0 | name = Eukaryotes | fossil_range = [[Proterozoic]] - Recent | image = Ostreococcus RCC143.jpg | image_caption = ''[[Ostreococcus]]'' is the smallest known free living eukaryote with an average size of 0.8 µm. | superdomain = [[Neomura]] | domain='''Eukaryota''' | domain_authority=[[Robert Whittaker|Whittaker]] & [[Lynn Margulis|Margulis]],1978 | subdivision_ranks = [[Kingdom (biology)|Kingdoms]] | subdivision = <div style = "background: #D3D3A4; padding: 4px;"> [[Animal]]ia - Animals</div> <div style = "background: lightblue; padding: 4px;"> [[Fungus|Fungi]]</div> <div style = "background: #FFC8A0; padding: 4px;"> [[Amoebozoa]]</div> <div style = "background: lightgreen; padding: 4px;"> [[Plant]]ae - Plants</div> <div style = "background: greenyellow; padding: 4px;"> [[Chromalveolata]]</div> <div style = "background: lavender; padding: 4px;"> [[Rhizaria]]</div> <div style = "background: khaki; padding: 4px;"> [[Excavata]]</div> {{!}}- style="background:#e0d0b0;" {{!}} ! [[Alternative taxonomical classification|Alternative phylogeny]] {{!}}- {{!}} style="padding:0 .5em; text-align:left;" {{!}} * '''''[[Unikont]]a''''' ** '''[[Opisthokonta]]''' *** [[Metazoa]] *** [[Mesomycetozoa]] *** [[Choanozoa]] *** [[Eumycota]] ** [[Amoebozoa]] * '''''[[Bikonta]]''''' ** [[Apusozoa]] ** [[Rhizaria]] ** [[Excavata]] ** [[Archaeplastida]] ** [[Chromalveolata]] }} [[Animal]]s, [[plant]]s, [[fungus|fungi]], and [[protist]]s are '''eukaryotes''' ({{IPAEng|juːˈkærɪɒt}} or {{IPAEng|-oʊt}}), [[organism]]s whose [[Cell (biology)|cells]] are organized into complex structures enclosed within [[Cell membrane|membranes]]. The defining membrane-bound structure which differentiates eukaryotic cells from [[prokaryotic]] cells is the [[Cell nucleus|nucleus]]. The presence of a nucleus gives these organisms their name, which comes from the [[Greek language|Greek]] ευ, meaning "good/true", and κάρυον, "nut". Many eukaryotic cells contain other membrane-bound [[organelle]]s such as [[mitochondrion|mitochondria]], [[chloroplast]]s and [[Golgi apparatus|Golgi bodies]]. Eukaryotes often have unique [[flagella]] made of [[microtubule]]s in a 9+2 arrangement. [[Cell division]] in eukaryotes is different from organisms without a nucleus (prokaryotes). It involves separating the duplicated [[chromosome]]s, through movements directed by microtubules. There are two types of division processes. In [[mitosis]], one cell divides to produce two genetically-identical cells. In [[meiosis]], which is required in [[sexual reproduction]], one [[diploid]] cell (having two instances of each chromosome, one from each parent) undergoes [[Genetic recombination|recombination]] of each pair of parental chromosomes, and then two stages of cell division, resulting in four [[haploid]] cells ([[gametes]]). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes. Eukaryotes appear to be [[monophyletic]], and so make up one of the three [[domain (biology)|domains of life]]. The two other domains, [[bacteria]] and [[archaea]], are prokaryotes, and have none of the above features. But eukaryotes do share some aspects of their biochemistry with archaea, and so are grouped with archaea in the [[clade]] [[Neomura]]. ==Cell features== Eukaryotic cells are typically much larger than [[prokaryote]]s. They have a variety of internal membranes and structures, called [[organelle]]s, and a [[cytoskeleton]] composed of [[microtubule]]s, [[microfilament]]s, and [[intermediate filament]]s, which play an important role in defining the cell's organization and shape. Eukaryotic [[DNA]] is divided into several linear bundles called [[chromosome]]s, which are separated by a microtubular spindle during nuclear division. {{Endomembrane system diagram}} ===Internal membrane=== Eukaryotic cells include a variety of membrane-bound structures, collectively referred to as the [[endomembrane system]]. Simple compartments, called [[vesicle (biology)|vesicles]] or [[vacuole]]s, can form by budding off other membranes. Many cells ingest food and other materials through a process of [[endocytosis]], where the outer membrane invaginates and then pinches off to form a vesicle. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles. The nucleus is surrounded by a double membrane (commonly referred to as a [[nuclear envelope]]), with pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form what is called the [[endoplasmic reticulum]] or ER, which is involved in protein transport and maturation. It includes the Rough ER where [[ribosome]]s are attached, and the proteins they synthesize enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the Smooth ER. In most eukaryotes, this protein-carrying vesicles are released and further modified in stacks of flattened vesicles, called [[Golgi apparatus|Golgi bodies]] or dictyosomes. Vesicles may be specialized for various purposes.For instance, [[lysosome]]s contain enzymes that break down the contents of food vacuoles, and [[peroxisome]]s are used to break down [[peroxide]], which is toxic otherwise. Many protozoa have contractile vacuoles, which collect and expel excess water, and [[extrusome]]s, which expel material used to deflect predators or capture prey. In multicellular organisms, [[hormone]]s are often produced in vesicles. In higher plants, most of a cell's volume is taken up by a central vacuole, which primarily maintains its osmotic pressure. [[Image:Mitochondrie.svg|thumb|300px| Mitochondria structure: <br />1) [[Inner membrane]] <br />2) [[Outer membrane]] <br />3) [[Crista]] <br />4) [[Matrix (biology)|Matrix]] ]] ===Mitochondria and plastids=== [[Mitochondrion|Mitochondria]] are organelles found in nearly all eukaryotes. They are surrounded by double membranes (known as the [[Lipid bilayer|phospholipid bi-layer]]), the inner of which is folded into invaginations called cristae, where [[aerobic respiration]] takes place. They contain their own DNA and ribosomes and are only formed by the fission of other mitochondria. They are now generally held to have developed from [[endosymbiosis|endosymbiotic]] prokaryotes, probably [[proteobacteria]]. The few protozoa that lack mitochondria have been found to contain mitochondrion-derived organelles, such as [[hydrogenosome]]s and [[mitosome]]s. Plants and various groups of [[alga]]e also have [[plastid]]s. Again, these have their own DNA and developed from endosymbiotes, in this case [[cyanobacteria]]. They usually take the form of [[chloroplast]]s, which like cyanobacteria contain [[chlorophyll]] and produce energy through [[photosynthesis]]. Others are involved in storing food. Although plastids likely had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion. Endosymbiotic origins have also been proposed for the nucleus, for which see below, and for eukaryotic [[flagellum|flagella]], supposed to have developed from [[spirochaete]]s. This is not generally accepted, both from a lack of [[Cell biology|cytological]] evidence and difficulty in reconciling this with cellular reproduction. ===Cytoskeletal structures=== Many eukaryotes have long slender motile cytoplasmic projections, called [[flagellum|flagella]]. These are composed mainly of [[tubulin]] and shorter [[cilium|cilia]], both of which are variously involved in movement, feeding, and sensation. These are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a [[basal body]], also called a [[kinetosome]] or [[centriole]], characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs, or [[mastigonemes]], and scales connecting membranes and internal rods. Their interior is continuous with the cell's [[cytoplasm]]. Microfilamental structures composed by [[actin]] and actin binding proteins, e.g., α-[[actinin]], [[fimbrin]], [[filamin]] are present in submembraneous cortical layers and bundles, as well. [[Motor protein]]s of microtubules, e.g., [[dynein]] or [[kinesin]] and actin, e.g., [[myosins]] provide dynamic character of the network. [[Centrioles]] are often present even in cells and groups that do not have flagella. They generally occur in groups of one or two, called [[kinetids]], that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles may also be associated in the formation of a spindle during nuclear division. Significance of cytoskeletal structures is underlined in determination of shape of the cells, as well as their being essential components of migratory responses like [[chemotaxis]] and [[chemokinesis]]. Some protists have various other microtubule-supported organelles. These include the [[radiolaria]] and [[heliozoa]], which produce [[axopodia]] used in flotation or to capture prey, and the [[haptophyte]]s, which have a peculiar flagellum-like organelle called the [[haptonema]]. ===Plant cell wall=== {{Further|[[Cell wall]]}} Plant cells have a cell wall, a fairly rigid layer outside the [[cell membrane]], providing the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell. The major carbohydrates making up the primary cell wall are [[cellulose]], [[hemicellulose]], and [[pectin]]. The cellulose [[microfibril]]s are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is [[xyloglucan]]. ==Differences between eukaryotic cells== There are many different types of eukaryotic cells, though animals and plants are the most familiar eukaryotes, and thus provide an excellent starting point for understanding eukaryotic structure. Fungi and many protists have some substantial differences, however. ===Animal cell=== [[Image:Animal_cell_structure_en.svg|thumb|350px|right|Structure of a typical animal cell.]] [[Image:Plant cell structure svg.svg|thumb|350px|Structure of a typical [[plant cell]].]] An '''animal cell''' is a form of [[eukaryotic cell]] that makes up many [[Biological tissue|tissues]] in [[animal]]s. The animal cell is distinct from other eukaryotes, most notably [[plant cells]], as they lack [[cell wall]]s and [[chloroplast]]s, and they have smaller [[vacuole]]s. Due to the lack of a rigid [[cell wall]], animal cells can adopt a variety of shapes, and a [[phagocyte|phagocytic]] cell can even engulf other structures. There are many different [[cell types]]. For instance, there are approximately 210 [[distinct cell types in the adult human body]]. ===Plant cell=== {{Further|[[Plant cell]]}} Plant [[cell (biology)|cells]] are quite different from the cells of the other eukaryotic organisms. Their distinctive features are: * A large central [[vacuole]] (enclosed by a membrane, the [[tonoplast]]), which maintains the cell's [[turgor]] and controls movement of [[molecule]]s between the [[cytosol]] and [[plant sap|sap]] * A primary [[cell wall]] containing [[cellulose]], [[hemicellulose]] and [[pectin]], deposited by the [[protoplast]] on the outside of the [[cell membrane]]; this contrasts with the cell walls of [[fungus|fungi]], which contain [[chitin]], and the [[cell envelope]]s of [[prokaryote]]s, in which [[peptidoglycan]]s are the main structural molecules * The [[plasmodesmata]], linking pores in the cell wall that allow each plant cell to communicate with other adjacent cells; this is different from the functionally analogous system of [[gap junction]]s between animal cells. * [[Plastid]]s, especially [[chloroplast]]s that contain [[chlorophyll]], the pigment that gives [[plant]]s their green color and allows them to perform [[photosynthesis]] * Higher plants, including [[Pinophyta|conifers]] and [[flowering plant]]s (Angiospermae) lack the [[flagellum|flagellae]] and [[centriole]]s that are present in [[animal cell]]s. ===Fungal cell=== '''Fungal cells''' are most similar to animal cells, with the following exceptions: * A cell wall containing [[chitin]] * Less definition between cells; the [[hypha]]e of higher fungi have porous partitions called [[septum|septa]], which allow the passage of cytoplasm, organelles, and, sometimes, nuclei. Primitive fungi have few or no septa, so each organism is essentially a giant multinucleate supercell; these fungi are described as [[coenocytic]]. * Only the most primitive fungi, [[chytrid]]s, have flagella. ===Other eukaryotic cells=== Eukaryotes are a very diverse group, and their cell structures are equally diverse. Many have cell walls; many do not. Many have chloroplasts, derived from primary, secondary, or even tertiary endosymbiosis; and many do not. Some groups have unique structures, such as the cyanelles of the [[glaucophyte]]s, the haptonema of the [[haptophyte]]s, or the ejectisomes of the [[cryptomonad]]s. Other structures, such as [[pseudopod]]s, are found in various eukaryote groups in different forms, such as the lobose [[amoebozoa]]ns or the reticulose [[foraminiferan]]s. ==Reproduction== Nuclear division is often coordinated with [[cell division]]. This generally takes place by [[mitosis]], a process that allows each daughter nucleus to receive one copy of each chromosome. In most eukaryotes, there is also a process of sexual reproduction, typically involving an alternation between [[haploid]] generations, wherein only one copy of each chromosome is present, and [[diploid]] generations, wherein two are present, occurring through nuclear fusion (syngamy) and [[meiosis]]. There is considerable variation in this pattern, however. Eukaryotes have a smaller surface to volume area ratio than prokaryotes, and thus have lower metabolic rates and longer generation times. In some multicellular organisms, cells specialized for metabolism will have enlarged surface areas, such as intestinal vili. ==Origin and evolution== [[Image:Collapsed tree labels simplified.png|thumb|350px|right|[[Phylogenetic tree]] showing the relationship between the eukaryotes and other forms of life.<ref>{{cite journal |author=Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P |title=Toward automatic reconstruction of a highly resolved tree of life |journal=Science |volume=311 |issue=5765 |pages=1283–7 |year=2006 |pmid=16513982 |doi=10.1126/science.1123061}}</ref> Eukaryotes are colored red, [[archaea]] green and [[bacteria]] blue.]] The origin of the eukaryotic cell was a milestone in the evolution of life, since they include all complex cells and almost all multi-cellular organisms. The timing of this series of events is hard to determine; [[Andrew H. Knoll|Knoll]] (1992) suggests they developed approximately 1.6 - 2.1 billion years ago. Some [[acritarch]]s are known from at least 1650 million years ago, and the possible alga ''[[Grypania]]'' has been found as far back as 2100 million years ago. <ref> {{cite journal | first = Andrew H. | last = Knoll | coauthors = Javaux, E.J, Hewitt, D. and Cohen, P. | title = Eukaryotic organisms in Proterozoic oceans | journal = Philosophical Transactions of the Royal Society of London, Part B | year=2006 | volume=361 | issue=1470 | pages=1023–1038 | url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1578724 | doi = 10.1098/rstb.2006.1843 | pmid = 16754612 }} </ref> Fossils that are clearly related to modern groups start appearing around 1.2 billion years ago, in the form of a [[red algae#Fossil record|red alga]]. [[Biomarker]]s suggest that at least [[stem group|stem]] eukaryotes arose even earlier. The presence of [[sterane]]s in [[Australia]]n [[shale]]s indicates that eukaryotes were present 2.7 billion years ago.<ref>[http://www.sciencemag.org/cgi/content/abstract/285/5430/1033 Archean Molecular Fossils and the Early Rise of Eukaryotes], by [[Jochen Brocks]] ''et al.'', Science, 13 Aug. 1999, pp. 1033-6.</ref> <ref>[http://www.newscientist.com/channel/life/mg19726421.900-mass-extinctions-the-microbes-strike-back.html Mass extinctions: the microbes strike back] by [[Peter Ward (paleontologist)|Peter Ward]], [[New Scientist]], 9 Feb. 2008, pp. 40-3.</ref> [[rRNA]] trees constructed during the 1980s and 1990s left most eukaryotes in an unresolved "crown" group (not technically a true [[crown group|crown]]), which was usually divided by the form of the mitochondrial cristae. The few groups that lack [[mitochondria]] branched separately, and so the absence was believed to be primitive; but this is now considered an artifact of [[long-branch attraction]], and they are known to have lost them secondarily.<ref>{{cite journal |author=Tovar J, Fischer A, Clark CG |title=The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica |journal=Mol. Microbiol. |volume=32 |issue=5 |pages=1013–21 |year=1999 |pmid=10361303 |doi=10.1046/j.1365-2958.1999.01414.x}}</ref><ref>{{cite journal |author=Boxma B, de Graaf RM, van der Staay GW, ''et al'' |title=An anaerobic mitochondrion that produces hydrogen |journal=Nature |volume=434 |issue=7029 |pages=74–9 |year=2005 |pmid=15744302 | doi = 10.1038/nature03343 <!--Retrieved from PMID by DOI bot-->}}</ref> Trees based on [[actin]] and other [[molecule]]s have painted a different and more complete picture. Most eukaryotes are now included in one of the following supergroups, although the relationship between these groups, and the [[monophyly]] of each group, is not yet clear:<ref>{{cite journal | author = Burki F, Shalchian-Tabrizi K, Minge M, Skjæveland Å, Nikolaev SI, et al. | year = 2007 | title = Phylogenomics Reshuffles the Eukaryotic Supergroups | journal = PLoS ONE | volume = 2 | issue = 8: e790 | doi = 10.1371/journal.pone.0000790 | pages = e790}}</ref><ref>{{cite journal | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1713255 | title = Evaluating Support for the Current Classification of Eukaryotic Diversity | author = Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz | doi = 10.1371/journal.pgen.0020220 | journal = PLoS Genet. | date = 2006 December | volume = 2 | issue = 12 | pages = e220 | pmid = 17194223 }}</ref> {| width="100%" cellspacing=0 | [[Opisthokont]]s || [[Animal]]s, [[fungus|fungi]], [[choanoflagellate]]s, etc. |- | [[Amoebozoa]] || Most lobose [[amoeba]]e and [[slime mould]]s |- | [[Rhizaria]] || [[Foraminifera]], [[Radiolaria]], and various other [[amoeboid]] protozoa |- | [[Excavate]]s || Various [[flagellate]] protozoa |- | [[Archaeplastida]] (or Primoplantae) || [[Embryophyte|Land plants]], [[green alga]]e, [[red alga]]e, and [[glaucophyte]]s |- | [[Chromalveolate]]s || [[Heterokont]]s, [[Haptophyte]]s, [[Cryptomonad]]s, and [[Alveolate]]s. |} {{userboxtop|toptext=&nbsp;}} {{clade| style=font-size:75%;line-height:75% | label1='''''Eukarya''''' | 1={{clade | label1=''[[Bikonta]]'' | 1={{clade | label1= | 1=''[[Apusozoa]]'' | label2= | 2=''[[Archaeplastida]]'' | label3= | 3=''[[Chromalveolata]]'' | label4= | 4=''[[Rhizaria]]'' | label5= | 5=''[[Excavata]]'' }} | label2=''[[Unikonta]]'' | 2={{clade | 1=''[[Amoebozoa]]'' | label2=''[[Opisthokonta]]'' | 2={{clade | label1= | 1=''[[Metazoa]]'' | label2= | 2=''[[Choanozoa]]'' | label3= | 3=''[[Eumycota]]'' }} }} }} }} <center><small>Likely cladogram of Eukarya</small></center> {{userboxbottom}} Several authorities recognize two larger clades, the [[unikont]]s and the [[bikont]]s, that derive from an ancestral uniflagellar organism and a biflagellate respectively. In this system, the opisthokonts and amoebozoans are considered unikonts, and the rest bikonts. The [[chromalveolate]]s were originally thought to be two separate groups, the [[chromista|chromists]] and the [[alveolate]]s, but the former was proved to be paraphyletic to the latter, and the two groups combined. Some small protist groups have not been related to any of these supergroups, in particular the [[centrohelid]]s. Eukaryotes are closely related to [[Archaea]], at least in terms of nuclear DNA and genetic machinery, and some place them with Archaea in the clade [[Neomura]]. In other respects, such as membrane composition, they are similar to [[Bacteria|eubacteria]]. Three main explanations for this have been proposed: * Eukaryotes resulted from the complete fusion of two or more cells, where the cytoplasm formed from a eubacterium, and the nucleus from an archaeon,<ref>{{cite journal |author=Martin W |title=Archaebacteria (Archaea) and the origin of the eukaryotic nucleus |journal=Curr. Opin. Microbiol. |volume=8 |issue=6 |pages=630–7 |year=2005 |month=December |pmid=16242992 |doi=10.1016/j.mib.2005.10.004}}</ref> or [[Viral Eukaryogenesis|from a virus]].<ref>{{cite journal |author=Takemura M |title=Poxviruses and the origin of the eukaryotic nucleus |journal=J. Mol. Evol. |volume=52 |issue=5 |pages=419–25 |year=2001 |month=May |pmid=11443345 |doi=10.1007/s002390010171}}</ref><ref>{{cite journal |author=Bell PJ |title=Viral eukaryogenesis: was the ancestor of the nucleus a complex DNA virus? |journal=J. Mol. Evol. |volume=53 |issue=3 |pages=251–6 |year=2001 |month=September |pmid=11523012 |doi=10.1007/s002390010215}}</ref> * Eukaryotes developed from Archaea, and acquired their eubacterial characteristics from the proto-mitochondrion. * Eukaryotes and Archaea developed separately from a modified eubacterium. The origins of the endomembrane system and mitochondria are also unclear.<ref>{{cite journal |author=Jékely G |title=Origin of eukaryotic endomembranes: a critical evaluation of different model scenarios |journal=Adv. Exp. Med. Biol. |volume=607 |issue= |pages=38–51 |year=2007 |pmid=17977457}}</ref> The '''phagotrophic hypothesis''' proposes that eukaryotic-type membranes lacking a cell wall originated first, with the development of endocytosis, while mitochondria were acquired by ingestion as endosymbionts.<ref>{{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 |year=2002 |month=March |pmid=11931142 |url=http://ijs.sgmjournals.org/cgi/pmidlookup?view=long&pmid=11931142}}</ref> The '''syntrophic hypothesis''' proposes that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it. Here the membranes originated after the engulfment of the mitochondrion, in part thanks to mitochondrial genes (the [[hydrogen hypothesis]] is one particular version).<ref>{{cite journal |author=Martin W, Müller M |title=The hydrogen hypothesis for the first eukaryote |journal=Nature |volume=392 |issue=6671 |pages=37–41 |year=1998 |month=March |pmid=9510246 |doi=10.1038/32096}}</ref> In a study using genomes to construct supertrees, Pisani ''et al'' (2007) suggest that, along with evidence that there was never a mitochondrion-less eukaryote, eukaryotes evolved from a [[syntrophy]] between an archaea closely related to [[Thermoplasmatales]] and an [[Proteobacteria|α-proteobacterium]], likely a [[symbiosis]] driven by sulfur or hydrogen. The mitochondrion and its genome is a remnant of the α-proteobacterial endosymbiont.<ref>{{cite journal | title=Supertrees disentangle the chimerical origin of eukaryotic genomes| author=Pisani D, Cotton JA, McInerney JO| journal= Mol Biol Evol.| year=2007| volume=24| issue=8| pages=1752–60| pmid=17504772 | doi=10.1093/molbev/msm095}}</ref> ==See also== * [[List of sequenced eukaryotic genomes]] ==References== <!-- ---------------------------------------------------------- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for a discussion of different citation methods and how to generate footnotes using the <ref>, </ref> and <reference /> tags ----------------------------------------------------------- --> <div class="references-small"> <references /> * {{cite journal | author=Knoll AH | title=The early evolution of eu-karyotes: A geological perspective | journal=Science | year=1992 | volume=256 | pages=622–27 | doi=10.1126/science.1585174 | issue=5057 | pmid=1585174 }} * {{cite journal | author=T. Cavalier-Smith | title=The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa | journal=International Journal of Systematic and Evolutionary Microbiology | year=2002 | volume=52 | pages=297–354 }} * {{cite journal | author=W. Martin & M.J. Russell | title=On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells | journal=Philosophical Transactions of the Royal Society B | year=1992 }} * {{cite journal | author=S. L. Baldauf | title=The Deep Roots of Eukaryotes | journal=[[Science (journal)|Science]] | year=2003 | volume=300 | pages=1703–1706 | doi=10.1126/science.1085544 | issue=5626 | pmid=12805537 }} * {{cite journal | author=Sina M. Adl ''et al'' | title=The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists | journal=Journal of Eukaryotic Microbiology | year=2005 | volume=52 | issue=5 | pages=399 | doi= 10.1111/j.1550-7408.2005.00053.x }} {{NCBI-scienceprimer}} </div> ==External links== {{wikispecies|Eukaryota}} * [http://www.tolweb.org/Eukaryotes/ Eukaryotes (Tree of Life web site)] * [http://wiki.biomine.skelleftea.se/wiki/index.php/Prokaryote_versus_eukaryote Prokaryote versus eukaryote, BioMineWiki] [[Category:Eukaryotes| ]] [[ar:حقيقيات النوى]] [[an:Eukarya]] [[ast:Eukaryota]] [[bs:Eukarioti]] [[bg:Еукариоти]] [[ca:Eucariota]] [[cs:Eukaryota]] [[cy:Ewcaryot]] [[da:Eucaryota]] [[de:Eukaryoten]] [[et:Eukarüoodid]] [[es:Eukaryota]] [[eo:Eŭkariotoj]] [[eu:Eukarioto]] [[fa:یوکاریوت]] [[fr:Eukaryota]] [[ga:Eocarót]] [[gl:Eukaryota]] [[ko:진핵생물]] [[hi:यूकैरियोट]] [[hsb:Eukarioty]] [[hr:Eukarioti]] [[id:Eukariota]] [[is:Heilkjörnungar]] [[it:Eukaryota]] [[he:איקריוטיים]] [[pam:Eukaryote]] [[la:Eucaryota]] [[lv:Eikariots]] [[lb:Eukaryoten]] [[lt:Eukariotas]] [[hu:Eukarióták]] [[nl:Eukaryoten]] [[ja:真核生物]] [[no:Eukaryoter]] [[nn:Eukaryotar]] [[nov:Eukaryota]] [[oc:Eukaryota]] [[nds:Eukaryota]] [[pl:Jądrowce]] [[pt:Eukaryota]] [[ro:Eucariote]] [[ru:Эукариоты]] [[sq:Eukarioti]] [[scn:Eukaryota]] [[simple:Eukaryote]] [[sk:Eukaryoty]] [[sl:Evkarionti]] [[sr:Еукариоте]] [[su:Eukariot]] [[fi:Aitotumaiset]] [[sv:Eukaryoter]] [[tl:Eukaryote]] [[th:ยูแคริโอต]] [[vi:Sinh vật nhân chuẩn]] [[tr:Ökaryot]] [[uk:Домен Ядерні]] [[wa:Eucariote]] [[zh:真核生物]]