{{Short description|Basic unit of life forms}} {{About|the basic unit of lifeforms|the branch of biology that studies them|Cell biology}} {{Protection padlock|small=yes}} {{pp-move}} {{Infobox anatomy |Name = Cell |Image =Typical human cell.tif |Caption =Diagram of typical generalised human cell (eukaryotic) |Image2 = celltypes.svg |Caption2 = A eukaryotic cell as in animals (left) compared to a prokaryotic cell as in bacteria (right) }}
The '''cell''' is the basic structural and functional unit of all forms of life or organisms. The term comes from the Latin word {{lang|la|cellula}} meaning 'small room'. A biological cell basically consists of a semipermeable cell membrane enclosing cytoplasm that contains genetic material. Most cells are only visible under a microscope. Except for highly-differentiated cell types (examples include red blood cells and gametes) most cells are capable of replication, and protein synthesis. Some types of cell are motile. Cells emerged on Earth about four billion years ago.
All organisms are grouped into prokaryotes, and eukaryotes. Prokaryotes are single-celled and include archaea and bacteria. Eukaryotes can be single-celled or multicellular, and include protists, plants, animals, most species of fungi, and some species of algae. All multicellular organisms are made up of many different types of cell. The diploid cells that make up the body of a plant or animal are known as somatic cells, which excludes the haploid gametes.
Prokaryotes lack a membrane-bound nucleus and have a nucleoid instead. In eukaryotic cells, the nucleus is enclosed in the nuclear membrane. Eukaryotic cells contain other membrane-bound organelles such as mitochondria, which provide energy for cell functions, and chloroplasts, in plants that create sugars by photosynthesis. Other membrane-less organelles may be proteinaceous, such as the ribosomes present (though different) in both groups. A unique membrane-bound prokaryotic organelle, the magnetosome has been discovered in magnetotactic bacteria.
Cells were discovered by Robert Hooke in 1665, who named them after their resemblance to cells in a monastery. Cell theory, developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all organisms, and that all cells come from pre-existing cells.
== Types == Organisms are broadly grouped into eukaryotes and prokaryotes. Eukaryotic cells possess a membrane-bound nucleus, and prokaryotic cells lack a nucleus but have a nucleoid region.<ref name="Cooper-2000">{{cite web |last1=Cooper |first1=Geoffrey M. |title=The Origin and Evolution of Cells |url=https://www.ncbi.nlm.nih.gov/books/NBK9841/ |website=The Cell: A Molecular Approach. 2nd edition |publisher=Sinauer Associates |access-date=17 September 2025 |language=en |date=2000}}</ref> Prokaryotes are single-celled organisms, whereas eukaryotes can be either single-celled or multicellular. Single-celled eukaryotes include microalgae such as diatoms. Multicellular eukaryotes include all animals, and plants, most fungi, and some species of algae.<ref>{{Cite web |title=Prokaryote structure |url=https://www.khanacademy.org/test-prep/mcat/cells/prokaryotes-bacteria/a/prokaryote-structure |access-date=2025-08-16 |website=khanacademy |language=en}}</ref><ref>{{cite journal |title=The Multiple Origins of Complex Multicellularity |first=Andrew H. |last=Knoll |journal=Annual Review of Earth and Planetary Sciences |volume=39 |pages=217–239 |year=2011 |doi=10.1146/annurev.earth.031208.100209 |bibcode=2011AREPS..39..217K }}</ref><ref name="libretext">{{cite web |title=24.1B: Fungi Cell Structure and Function |url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/24%3A_Fungi/24.01%3A_Characteristics_of_Fungi/24.1B%3A_Fungi_Cell_Structure_and_Function |website=Biology LibreTexts |access-date=3 October 2025 |language=en |date=15 July 2018}}</ref> {|class="wikitable plainrowheaders" |- ! Property ! Archaea !width="27%"|Bacteria ! Eukaryota |- ! scope=row |Cell membrane |Ether-linked lipids |Ester-linked lipids |Ester-linked lipids |- ! scope=row |Cell wall |Glycoprotein, or S-layer; rarely pseudopeptidoglycan |Peptidoglycan, S-layer, or no cell wall |Various structures; animal cells lack a cell wall |- ! scope=row |Gene structure |Circular chromosomes, similar translation and transcription to Eukaryota |Circular chromosomes, unique translation and transcription |Multiple, linear chromosomes, but translation and transcription similar to Archaea |- ! scope=row |Internal cell structure |No nucleus; rarely has membrane-bound organelles<ref>{{cite journal |vauthors=Heimerl T, Flechsler J, Pickl C, Heinz V, Salecker B, Zweck J, Wanner G, Geimer S, Samson RY, Bell SD, Huber H, Wirth R, Wurch L, Podar M, Rachel R |title=A Complex Endomembrane System in the Archaeon ''Ignicoccus hospitalis'' Tapped by ''Nanoarchaeum equitans'' |journal=Frontiers in Microbiology |volume=8 |article-number=1072 |date=13 June 2017 |pmid=28659892 |pmc=5468417 |doi=10.3389/fmicb.2017.01072 |doi-access=free }}</ref> |No nucleus, has a few membrane-bound prokaryotic organelles |Has nucleus and other membrane-bound organelles |- ! scope=row |Metabolism<ref>{{cite book |vauthors=Jurtshuk P |chapter=Bacterial Metabolism |title=Medical Microbiology |date=1996 |publisher=University of Texas Medical Branch at Galveston |location=Galveston (TX) |pmid=21413278 |edition=4th |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK7919/ |ref=Medical Microbiology |isbn=978-0-9631172-1-2 }}</ref> |Various, including diazotrophy, with methanogenesis unique to Archaea |Various, including photosynthesis, aerobic and anaerobic respiration, fermentation, diazotrophy, and autotrophy |Photosynthesis, cellular respiration, and fermentation; no diazotrophy |- ! scope=row |Reproduction |Asexual reproduction, horizontal gene transfer |Asexual reproduction, horizontal gene transfer |Sexual and asexual reproduction |- ! scope=row |{{nowrap|'''Protein synthesis initiation'''}} |Methionine |Formylmethionine |Methionine |- ! scope=row |RNA polymerase |One |One |Many |- ! scope=row |EF-2/EF-G |Sensitive to diphtheria toxin |Resistant to diphtheria toxin |Sensitive to diphtheria toxin |}
=== Prokaryotes === {{main|Prokaryote}}
[[File:Average prokaryote cell- en.svg|thumb|upright=0.7|Structure of a typical bacterial cell, generally similar with the archaeal cell structure. The bacterial flagellum shown, differs from the archaellum in archaea]] [[File:Binary fission.svg|thumb|upright=0.7|Bacteria and archaea divide by binary fission]]
All prokaryotes are single-celled and include bacteria and archaea, two of the three domains of life.<ref>{{Citation |last=Cole |first=Laurence A. |title=Chapter 13 - Evolution of Chemical, Prokaryotic, and Eukaryotic Life |date=2016-01-01 |work=Biology of Life |pages=93–99 |editor-last=Cole |editor-first=Laurence A. |publisher=Academic Press |doi=10.1016/b978-0-12-809685-7.00013-7 |isbn=978-0-12-809685-7 }}</ref> Prokaryotic cells were likely the first form of life on Earth,<ref name="Poole">{{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 |url=}}</ref> characterized by having vital biological processes including cell signaling. They are simpler and smaller than eukaryotic cells, lack a nucleus, and the other usually present membrane-bound organelles.<ref name="Fowler">{{Cite web |last1=Fowler |first1=Samantha |last2=Roush |first2=Rebecca |last3=Wise |first3=James |date=2013-04-25 |title=3.2 Comparing Prokaryotic and Eukaryotic Cells - Concepts of Biology {{!}} OpenStax |url=https://openstax.org/books/concepts-biology/pages/3-2-comparing-prokaryotic-and-eukaryotic-cells |access-date=2025-08-22 |website=openstax.org}}</ref> Prokaryotic organelles are less complex, and are typically membrane-less.<ref>{{cite journal |title=Organelle Formation in Bacteria and Archaea |display-authors=1 |first1=Carly R. |last1=Grant |first2=Juan |last2=Wan |first3=Arash |last3=Komeili |journal=Annual Review of Cell and Developmental Biology |volume=34 |date=October 2018 |pages=217–238 |doi=10.1146/annurev-cellbio-100616-060908 |pmid=30113887 }}</ref> All prokaryotic cells secrete different substances from their membranes, including exoenzymes, and extracellular polymeric substances.
Most prokaryotes are the smallest of all organisms, ranging from 0.1 to 5.0 μm in diameter.<ref name="Black 2004 p.">{{cite book |last=Black |first=Jacquelyn G. |title=Microbiology |publisher=Wiley |publication-place=New York Chichester |date=2004 |isbn=978-0-471-42084-2 |page=78}}</ref> The largest bacterium known, ''Thiomargarita magnifica'', is visible to the naked eye with an average length of {{Val|1|u=cm}}, but can be as much as {{Val|2|u=cm}}<ref>{{cite journal |display-authors=1 |last1=Volland |first1=Jean-Marie |last2=Gonzalez-Rizzo |first2=Silvina |last3=Gros |first3=Olivier |last4=Tyml |first4=Tomáš |last5=Ivanova |first5=Natalia |last6=Schulz |first6=Frederik |last7=Goudeau |first7=Danielle |last8=Elisabeth |first8=Nathalie H. |last9=Nath |first9=Nandita |last10=Udwary |first10=Daniel |last11=Malmstrom |first11=Rex R. |last12=Guidi-Rontani |first12=Chantal |last13=Bolte-Kluge |first13=Susanne |last14=Davies |first14=Karen M. |last15=Jean |first15=Maïtena R. |last16=Mansot |first16=Jean-Louis |last17=Mouncey |first17=Nigel J. |last18=Angert |first18=Esther R. |last19=Woyke |first19=Tanja |last20=Date |first20=Shailesh V. |title=A centimeter-long bacterium with DNA contained in metabolically active, membrane-bound organelles |journal=Science |date=June 24, 2022 |volume=376 |issue=6600 |pages=1453–1458 |issn=0036-8075 |eissn=1095-9203 |doi=10.1126/science.abb3634 |pmid=35737788 |bibcode=2022Sci...376.1453V |url=https://www.researchgate.net/publication/361513474 |biorxiv=10.1101/2022.02.16.480423 |s2cid=249990020 }}</ref><ref name="Pennisi">{{cite web |url=https://www.science.org/content/article/largest-bacterium-ever-discovered-has-unexpectedly-complex-cells |first=Elizabeth |last=Pennisi |author-link=Elizabeth Pennisi |title=Largest bacterium ever discovered has unexpectedly complex cells |date= |work=Science |publisher=science.org |access-date=2022-02-24 |language=en}}</ref>
====Bacteria==== {{Main|Bacterial cell structure}}
Bacteria are enclosed in a cell envelope, that protects the interior from the exterior.<ref>{{Cite journal |last1=Silhavy |first1=Thomas J. |last2=Kahne |first2=Daniel |last3=Walker |first3=Suzanne |date=2010-05-01 |title=The Bacterial Cell Envelope |url=http://cshperspectives.cshlp.org/content/2/5/a000414 |journal=Cold Spring Harbor Perspectives in Biology |language=en |volume=2 |issue=5 |article-number=a000414 |doi=10.1101/cshperspect.a000414 |issn=1943-0264 |pmc=2857177 |pmid=20452953}}</ref> It generally consists of a plasma membrane covered by a cell wall which, for some bacteria, is covered by a third gelatinous layer called a bacterial capsule. The capsule may be polysaccharide as in pneumococci, meningococci or polypeptide as ''Bacillus anthracis'' or hyaluronic acid as in streptococci. ''Mycoplasma'' only possess the cell membrane.<ref name="Larry">{{cite book |title=Structural and Functional Relationships in Prokaryotes |series=SpringerLink: Springer e-Books |first=Larry L. |last=Barton |publisher=Springer Science & Business Media |year=2005 |isbn=978-0-387-27125-5 |pages=69–71 |url=https://books.google.com/books?id=BTUvCHopWiEC&pg=PA69 }}</ref> The cell envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective mechanical and chemical filter.<ref name=Fuertes-Rabanal_et_al_2025/> The cell wall consists of peptidoglycan and acts as an additional barrier against exterior forces.<ref>{{cite book |title=The Bacterial Cell Wall |first1=Guntram |last1=Seltmann |first2=Otto |last2=Holst |publisher=Springer Science & Business Media |year=2013 |isbn=978-3-662-04878-8 |page=3 |url=https://books.google.com/books?id=j637CAAAQBAJ&pg=PA3 }}</ref><ref name=Fuertes-Rabanal_et_al_2025>{{cite journal |title=Cell walls: a comparative view of the composition of cell surfaces of plants, algae, and microorganisms |display-authors=1 |first1=María |last1=Fuertes-Rabanal |first2=Diego |last2=Rebaque |first3=Asier |last3=Largo-Gosens |first4=Antonio |last4=Encina |first5=Hugo |last5=Mélida |journal=Journal of Experimental Botany |volume=76 |issue=10 |date=July 2, 2025 |pages=2614–2645 |doi=10.1093/jxb/erae512 |pmid=39705009 |pmc=12223506 }}</ref> The cell wall acts to protect the cell mechanically and chemically from its environment, and is an additional layer of protection to the cell membrane. It also prevents the cell from expanding and bursting (cytolysis) from osmotic pressure due to a hypotonic environment.<ref>{{cite book |title=Downstream Process Technology: A New Horizon In Biotechnology |first1=Krishna Kant |last1=Prasad |first2=Nooralabettu Krishna |last2=Prasad |publisher=PHI Learning Pvt. Ltd. |year=2010 |isbn=978-81-203-4040-4 |pages=116–117 |url=https://books.google.com/books?id=Z-RrbPSB2QQC&pg=PA117 }}</ref>
The DNA of a bacterium typically consists of a single circular chromosome that is in direct contact with the cytoplasm in a region called the nucleoid. Some bacteria contain multiple circular or even linear chromosomes.<ref name="Egan Fogel 2005">{{cite journal |last1=Egan |first1=Elizabeth S. |last2=Fogel |first2=Michael A. |last3=Waldor |first3=Matthew K. |title=MicroReview: Divided genomes: negotiating the cell cycle in prokaryotes with multiple chromosomes |journal=Molecular Microbiology |volume=56 |issue=5 |date=2005 |doi=10.1111/j.1365-2958.2005.04622.x |pages=1129–1138 |pmid=15882408 }}</ref><ref name="nature.com">{{Cite web |title=Genome Packaging in Prokaryotes {{!}} Learn Science at Scitable |url=http://www.nature.com/scitable/topicpage/genome-packaging-in-prokaryotes-the-circular-chromosome-9113 |access-date=2025-08-30 |website=www.nature.com}}</ref><ref>{{Cite web |title=The difference between nucleus and nucleoid |url=https://byjus.com/biology/difference-between-nucleus-and-nucleoid/ |access-date=2025-08-30 |website=BYJUS}}</ref> The cytoplasm also contains ribosomes and various inclusions where transcription takes place alongside translation.<ref name="NCBI">{{NCBI-scienceprimer |article=What Is a Cell? |url=https://web.archive.org/web/20130503014839/http://www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html |access-date=3 May 2013 |date=30 March 2004}}</ref><ref name="libretexts3">{{cite web |title=7.6C: Prokaryotic Transcription and Translation Are Coupled |url=https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/07%3A_Microbial_Genetics/7.06%3A_Translation-_Protein_Synthesis/7.6C%3A_Prokaryotic_Transcription_and_Translation_Are_Coupled |website=Biology LibreTexts |access-date=17 October 2025 |language=en |date=17 May 2017}}</ref> Extrachromosomal DNA as plasmids, are usually circular and encode additional genes, such as those of antibiotic resistance.<ref>{{cite book |title=Snyder and Champness Molecular Genetics of Bacteria |series=ASM Books |first1=Tina M. |last1=Henkin |first2=Joseph E. |last2=Peters |edition=5th |publisher=John Wiley & Sons |year=2020 |isbn=978-1-55581-975-0 |pages=181–189 |url=https://books.google.com/books?id=6-TxDwAAQBAJ&pg=PA181 }}</ref> Linear bacterial plasmids have been identified in several species of spirochete bacteria, including species of ''Borrelia'' which causes Lyme disease.<ref>{{cite web |title=Karyn's Genomes: Borrelia burgdorferi |publisher=European Bioinformatics Institute |work=2can on the EBI-EMBL database |url=http://www.ebi.ac.uk/2can/genomes/bacteria/Borrelia_burgdorferi.html |access-date=2013-05-06 |archive-url=https://web.archive.org/web/20130506040937/http://www.ebi.ac.uk/2can/genomes/bacteria/Borrelia_burgdorferi.html |archive-date=2013-05-06 }}</ref> The prokaryotic cytoskeleton in bacteria is involved in the maintenance of cell shape, polarity and cytokinesis.<ref name="Erickson2017">{{cite journal |vauthors=Erickson HP |title=The discovery of the prokaryotic cytoskeleton: 25th anniversary |journal=Mol Biol Cell |volume=28 |issue=3 |pages=357–358 |date=February 2017 |pmid=28137947 |pmc=5341718 |doi=10.1091/mbc.E16-03-0183 |url=}}</ref>
Compartmentalization is a key feature of eukaryotic cells but some species of bacteria, have protein-based organelle-like microcompartments such as gas vesicles, and carboxysomes, and encapsulin nanocompartments.<ref name="McDowell2022">{{cite journal |vauthors=McDowell HB, Hoiczyk E |title=Bacterial Nanocompartments: Structures, Functions, and Applications |journal=J Bacteriol |volume=204 |issue=3 |pages=e0034621 |date=March 2022 |article-number=e00346-21 |pmid=34606372 |pmc=8923211 |doi=10.1128/JB.00346-21 |url=}}</ref><ref name="Murat2010"/><ref>{{Cite journal |last1=Stewart |first1=Katie L. |last2=Stewart |first2=Andrew M. |last3=Bobik |first3=Thomas A. |date=2020-10-06 |title=Prokaryotic Organelles: Bacterial Microcompartments in E. coli and Salmonella |journal=EcoSal Plus |volume=9 |issue=1 |article-number=10.1128/ecosalplus.ESP–0025–2019 |doi=10.1128/ecosalplus.esp-0025-2019 |pmc=7552817 |pmid=33030141}}</ref><ref name="Adamiak">{{cite journal |vauthors=Adamiak N, Krawczyk KT, Locht C, Kowalewicz-Kulbat M |title=Archaeosomes and Gas Vesicles as Tools for Vaccine Development |journal=Front Immunol |volume=12 |issue= |article-number=746235 |date=2021 |pmid=34567012 |pmc=8462270 |doi=10.3389/fimmu.2021.746235 |doi-access=free |url=}}</ref> Certain membrane-bound prokaryotic organelles have also been discovered. They include the magnetosome of magnetotactic bacteria,<ref name="Murat2010">{{cite journal |last1=Murat |first1=D |last2=Byrne |first2=M |last3=Komeili |first3=A |title=Cell biology of prokaryotic organelles. |journal=Cold Spring Harbor Perspectives in Biology |date=October 2010 |volume=2 |issue=10 |article-number=a000422 |doi=10.1101/cshperspect.a000422 |pmid=20739411|pmc=2944366 }}</ref> and the anammoxosome of anammox bacteria.<ref name="de Almeida2015">{{cite journal |last1=de Almeida |first1=NM |last2=Neumann |first2=S |last3=Mesman |first3=RJ |last4=Ferousi |first4=C |last5=Keltjens |first5=JT |last6=Jetten |first6=MS |last7=Kartal |first7=B |last8=van Niftrik |first8=L |title=Immunogold Localization of Key Metabolic Enzymes in the Anammoxosome and on the Tubule-Like Structures of Kuenenia stuttgartiensis. |journal=Journal of Bacteriology |date=July 2015 |volume=197 |issue=14 |pages=2432–41 |doi=10.1128/JB.00186-15 |pmid=25962914 |pmc=4524196 }}</ref><ref name="Saier2013">{{cite journal |last1=Saier Jr. |first1=Milton H. |last2=Bogdanov |first2=Mikhail V. |title=Membranous Organelles in Bacteria |journal=Microbial Physiology |date=2013 |volume=23 |issue=1–2 |pages=5–12 |doi=10.1159/000346496 |pmid=23615191 }}</ref>
Cell-surface appendages can include flagella, and pili, protein structures that facilitate movement and communication between cells.<ref name="Kim">{{cite journal |last=Kim |first=K. W. |title=Electron microscopic observations of prokaryotic surface appendages |journal=Journal of Microbiology |volume=55 |pages=919–926 |year=2017 |issue=12 |doi=10.1007/s12275-017-7369-4 |pmid=29214488 }}</ref> The flagellum stretches from the cytoplasm through the cell membrane and extrudes through the cell wall.<ref>{{cite journal |title=Basal Organelles of Bacterial Flagella |first1=Germaine |last1=Cohen-Bazire |first2=Jack |last2=London |journal=Journal of Bacteriology |volume=94 |issue=2 |pages=458–465 |date=August 1967 |doi=10.1128/jb.94.2.458-465.1967 |pmid=6039362 |pmc=315060 }}</ref> Fimbriae are short attachment pili, the other type of pilus is the longer conjugative type.<ref name=Beeby_et_al_2020>{{cite journal |title=Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia |display-authors=1 |first1=Morgan |last1=Beeby |first2=Josie L. |last2=Ferreira |first3=Patrick |last3=Tripp |first4=Sonja-Verena |last4=Albers |first5=David R. |last5=Mitchell |journal=FEMS Microbiology Reviews |volume=44 |issue=3 |date=May 2020 |pages=253–304 |doi=10.1093/femsre/fuaa006 |pmid=32149348 }}</ref> Fimbriae are formed of an antigenic protein called pilin, and are responsible for the attachment of bacteria to specific receptors on host cells.<ref>{{cite book |title=Bacterial Pathogenesis: A Molecular Approach |series=ASM Books |display-authors=1 |first1=Brenda A. |last1=Wilson |first2=Malcolm |last2=Winkler |first3=Brian T. |last3=Ho |edition=4th |publisher=John Wiley & Sons |year=2020 |isbn=978-1-55581-941-5 |page=270 |url=https://books.google.com/books?id=q_72DwAAQBAJ&pg=PA270 }}</ref>
====Archaea==== {{Main|Archaea}}
Archaea are enclosed in a cell envelope consisting of a plasma membrane and a cell wall. An exception to this is the ''Thermoplasma'' that only has the cell membrane.<ref name="Larry"/> The cell membranes of archaea are unique, consisting of ether-linked lipids. The prokaryotic cytoskeleton has homologues of eukaryotic actin and tubulin.<ref name="Erickson2017"/> A unique form of metabolism in the archaean is methanogenesis. Their cell-surface appendage equivalent of the flagella is the differently structured and unique archaellum.<ref>{{Cite journal |last1=van Wolferen |first1=Marleen |last2=Pulschen |first2=Andre Arashiro |last3=Baum |first3=Buzz |last4=Gribaldo |first4=Simonetta |last5=Albers |first5=Sonja-Verena |date=November 2022 |title=The cell biology of archaea |journal=Nature Microbiology |language=en |volume=7 |issue=11 |pages=1744–1755 |doi=10.1038/s41564-022-01215-8 |pmid=36253512 |issn=2058-5276|pmc=7613921 }}</ref><ref name=Beeby_et_al_2020/> The DNA is contained in a circular chromosome in direct contact with the cytoplasm, in a region known as the nucleoid. Ribosomes are also found freely in the cytoplasm, or attached to the cell membrane where DNA processing takes place.<ref name="NCBI"/><ref>{{cite journal |last1=Ménétret |first1=Jean-François |last2=Schaletzky |first2=Julia |last3=Clemons |first3=William M. |last4=Osborne |first4=Andrew R. |last5=Skånland |first5=Sigrid S. |last6=Denison |first6=Carilee |last7=Gygi |first7=Steven P. |last8=Kirkpatrick |first8=Don S. |last9=Park |first9=Eunyong |last10=Ludtke |first10=Steven J. |last11=Rapoport |first11=Tom A |last12=Akey |first12=Christopher W. |display-authors=3 |title=Ribosome binding of a single copy of the SecY complex: implications for protein translocation |journal=Molecular Cell |volume=28 |issue=6 |pages=1083–1092 |date=December 2007 |pmid=18158904 |doi=10.1016/j.molcel.2007.10.034 |url=https://authors.library.caltech.edu/90566/2/1-s2.0-S1097276507008258-mmc1.pdf |doi-access=free |access-date=2020-09-01 |archive-date=2021-01-21 |archive-url=https://web.archive.org/web/20210121115905/https://authors.library.caltech.edu/90566/2/1-s2.0-S1097276507008258-mmc1.pdf |url-status=live }}</ref>
The archaea are noted for their extremophile species, and many are selectively evolved to thrive in extreme heat, cold, acidic, alkaline, or high salt conditions.<ref>{{cite journal |title=Extremophiles and Extreme Environments |first=Pabulo Henrique |last=Rampelotto |journal=Life |year=2013 |volume=3 |issue=3 |pages=482–485 |doi=10.3390/life3030482 |pmid=25369817 |pmc=4187170 |bibcode=2013Life....3..482R |doi-access=free }}</ref> There are no known archaean pathogens.<ref>{{cite journal |vauthors=Duller S, Moissl-Eichinger C |title=Archaea in the Human Microbiome and Potential Effects on Human Infectious Disease |journal=Emerg Infect Dis |volume=30 |issue=8 |pages=1505–13 |date=August 2024 |pmid=39043386 |pmc=11286065 |doi=10.3201/eid3008.240181 |url=}}</ref>
=== Eukaryotes === {{main|Eukaryote}} thumb|Diagram of a typical generalized eukaryotic cell A eukaryotic cell can be 2 to 100 times larger in diameter than a typical prokaryotic cell.<ref>{{Cite journal |last1=Bartee |first1=Lisa |last2=Shriner |first2=Walter |last3=Creech |first3=Catherine |date=2017 |title=Comparing Prokaryotic and Eukaryotic Cells |url=https://openoregon.pressbooks.pub/mhccmajorsbio/chapter/comparing-prokaryotic-and-eukaryotic-cells/ |website=OpenOregon Educational Resources}}</ref> Eukaryotes can be single-celled, as in diatoms (microscopic algae), or microfungi such as yeasts, or multicellular, as in animals, plants, most fungi, and seaweed (macroalgae).<ref>{{cite journal |last1=Lodé |first1=Thierry |title=For Quite a Few Chromosomes More: The Origin of Eukaryotes… |journal=Journal of Molecular Biology |date=October 2012 |volume=423 |issue=2 |pages=135–142 |doi=10.1016/j.jmb.2012.07.005 |pmid=22796299 }}</ref> Multicellular organisms are made up of many different types of cell known overall as somatic cells.<ref name="Genome2025">{{cite web |title=Somatic Cells |url=https://www.genome.gov/genetics-glossary/Somatic-Cells |website=www.genome.gov |access-date=19 September 2025 |language=en}}</ref> Eukaryotes are distinguished by the presence of a membrane-bound nucleus.<ref name="visiblebody">{{Cite web |author=Visible Body, part of Cengage Learning |title=Eukaryotic Chromosomes |url=https://www.visiblebody.com/learn/biology/dna-chromosomes/eukaryotic-chromosomes |access-date=2025-09-11 |website=www.visiblebody.com}}</ref> The nucleus gives the eukaryote its name, which means "true nut" or "true kernel", where "nut" means the nucleus.<ref>{{Cite web |title=More on Eukaryote Morphology |url=https://ucmp.berkeley.edu/alllife/eukaryotamm.html |access-date=2025-09-03 |website=ucmp.berkeley.edu}}</ref>
The nucleus is the largest mebrane-bound organelle in the eukaryotic cell. Other organelles present in all eukaryotic cells are the endoplasmic reticulum, ribosomes, the Golgi apparatus, mitochondria, lysosomes, peroxisomes, endosomes, and vesicles. The contents of the cell are contained within a cell membrane, and together with all the membranes of the organelles (except the mitochondria) are known as the endomembrane system.<ref name="libretext4"/> All of these membranes are involved in the secretory and endocytic pathways, modifying, packaging, and transporting proteins and lipids to and from the trans Golgi network.<ref name="Day2018">{{cite journal |vauthors=Day KJ, Casler JC, Glick BS |title=Budding Yeast Has a Minimal Endomembrane System |journal=Dev Cell |volume=44 |issue=1 |pages=56–72.e4 |date=January 2018 |pmid=29316441 |pmc=5765772 |doi=10.1016/j.devcel.2017.12.014 |url=}}</ref> In mammalian cells, endocytosis includes early, late, and recycling endosomes.<ref name="Day2018"/>
Some eukaryotes cells including plant cells and fungi have a cell wall. Plastids including chloroplasts feature mainly in plant cells. Most cell types include vaults. There are many cell variations among the different eukaryote groups. Many cells project one or more cellular extensions. And some organelles also project extensions such as stromules from plastids in plant cells, peroxules from peroxisomes, and matrixules from mitochondria.<ref name="Koenig2023">{{cite journal |last1=Koenig |first1=AM |last2=Liu |first2=B |last3=Hu |first3=J |title=Visualizing the dynamics of plant energy organelles. |journal=Biochemical Society transactions |date=20 December 2023 |volume=51 |issue=6 |pages=2029-2040 |doi=10.1042/BST20221093 |pmid=37975429}}</ref>
Most distinct cell types arise from a single totipotent cell, called a zygote, that differentiates into hundreds of different cell types during the course of development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of molecules during division).<ref>{{cite book |chapter=Asymmetric Behavior in Stem Cells |first=Bridget M. |last=Deasy |pages=13–22 |chapter-url=https://books.google.com/books?id=SnALU9lSISEC&pg=PA13 |editor1-last=Rajasekhar |editor1-first=V. K. |editor2-last=Vemuri |editor2-first=M. C. |title=Regulatory Networks in Stem Cells |series=Stem Cell Biology and Regenerative Medicine |date=2009 |publisher=Humana Press |isbn=978-1-60327-227-8 |doi=10.1007/978-1-60327-227-8_2 }}</ref>
Eukaryotic cell types include those that make up animals, plants, fungi, algae, and protists. All of which have many different species and cell differences. A separate grouping of animals and fungi are known as opisthokonts.
== Animal cells == {{Further|Animal embryonic development|Cell types}} thumb|upright=1.2|Structure of an animal cell [[File:Cell differentiation.jpg|thumb|Post-translational modifications as cell reprogramming involved in the differentiation of human pluripotent stem cells (hPSCs). (ICM - inner cell mass)]] [[File: Germ layers.jpg|thumb|upright=1.7| Cells from the germ layers]] All the cells in an animal body develop from one totipotent diploid cell called a zygote. During the embryonic development of an animal, the cells differentiate into the specialised tissues and organs of the organism. Different groups of cells differentiate from the germ layers. The sponge has only one layer. Some other animals known as diploblasts have two germ layers the ectoderm, and the endoderm. More advanced animals have an extra layer, the middle mesodermal layer, and are known as triploblastic. Triploblastic animals make up the large clade of Bilateria. Differentiation results in structural or functional changes to stem cells, and progenitor cells.
The ectoderm gives rise to several different types of epithelial tissues including the skin, and glands, and to the nervous tissue. Epithelium as mesothelium forms the lining of many organs, and inner cavities.<ref name="openstax5">{{cite web |last1=Betts |first1=J. Gordon |title=4.1 Types of Tissues - Anatomy and Physiology {{!}} OpenStax |url=https://openstax.org/books/anatomy-and-physiology/pages/4-1-types-of-tissues |website=openstax.org |access-date=18 December 2025 |language=English |date=25 April 2013}}</ref> Epithelial cells are joined together in sheets by way of cell junctions; adherens junctions, and desmosomes bind the cells together, and hemidesmosomes bind the cells to the basement membrane. All three types are linked to the cell cytoskeleton.<ref name="ECB">{{cite book |last1=Alberts |first1=Bruce |last2=Hopkin |first2=Karen |last3=Johnson |first3=Alexander |last4=Morgan |first4=David |last5=Raff |first5=Martin |last6=Roberts |first6=Keith |last7=Walter |first7=Peter |title=Essential cell biology |date=2004 |publisher=Garland |location=New York |isbn=0-8153-3481-8 |page=712 |edition=2.}}</ref>
There are an estimated 200 different cell types in the human body. The estimated cell count in a typical adult human body is around 30 trillion cells, 36 trillion in an adult male, and 28 trillion in a female.<ref name="Khan2025"/>
===Structure=== An animal cell has a cell membrane that surrounds a gel-like cytoplasm. The cytoplasm contains the cytoskeleton, the cell nucleus, the endoplasmic reticulum, ribosomes, the Golgi apparatus, mitochondria, lysosomes, peroxisomes, endosomes, vacuoles and vesicles, and vaults. An animal cell structure, as other eukaryotes, includes an endomembrane system encompassing the cell membrane, and all the membranes of the organelles excluding those of the mitochondria.The whole system cooperates in the modification, packaging, and transport of proteins and lipids.<ref name="libretext4">{{cite web |title=4.4: The Endomembrane System |url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Map%3A_Raven_Biology_12th_Edition/04%3A_Cell_Structure/4.04%3A_The_Endomembrane_System |website=Biology LibreTexts |access-date=18 November 2025 |language=en |date=5 December 2021}}</ref>
===Cell membrane=== {{Main|Cell membrane}}
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The cell membrane, or plasma membrane, is a selectively permeable membrane as an outer boundary of the cell that encloses the cytoplasm.<ref name="NIH">{{cite web |title= Inside the Cell |url=https://publications.nigms.nih.gov/insidethecell/pdf/inside_the_cell.pdf |website=publications.nigms.nih.gov |access-date=22 September 2025 |archive-date=28 July 2017 |archive-url=https://web.archive.org/web/20170728005920/https://publications.nigms.nih.gov/insidethecell/pdf/inside_the_cell.pdf }}</ref> Underlying, and attached to the cell membrane is the cell cortex, the outermost part of the actin cytoskeleton.<ref name="Zhu2024">{{cite journal |vauthors=Zhu H, Miao R, Wang J, Lin M |title=Advances in modeling cellular mechanical perceptions and responses via the membrane-cytoskeleton-nucleus machinery |journal=Mechanobiol Med |volume=2 |issue=1 |article-number=100040 |date=March 2024 |pmid=40395451 |pmc=12082147 |doi=10.1016/j.mbm.2024.100040 |url=}}</ref> The membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a lipid bilayer of phospholipids, which are amphiphilic (partly hydrophobic and partly hydrophilic). It has been best described in the fluid mosaic model.<ref>{{cite journal |title=The Fluid Mosaic Model of the Structure of Cell Membranes: Cell membranes are viewed as two-dimensional solutions of oriented globular proteins and lipids |first1=S. J. |last1=Singer |first2=Garth L. |last2=Nicolson |journal=Science |date=February 18, 1972 |volume=175 |issue=4023 |pages=720–731 |doi=10.1126/science.175.4023.720 |pmid=4333397 }}</ref>
Embedded within the cell membrane are secretory macromolecular lipoprotein structures called porosomes;<ref name="Jena2015">{{cite journal |last1=Jena |first1=Bhanu P. |title='Porosome' discovered nearly 20 years ago provides molecular insights into the kiss-and-run mechanism of cell secretion |journal=Journal of Cellular and Molecular Medicine |date=July 2015 |volume=19 |issue=7 |pages=1427–1440 |doi=10.1111/jcmm.12598|pmid=26033351 |pmc=4511343 }}</ref> and a number of different channels and pumps involved in actively transporting molecules into and out of the cell.<ref name="NCBI"/> The membrane is semi-permeable, and selectively permeable, in that it can either let a substance (molecule or ion) pass through freely, to a limited extent or not at all.<ref>{{cite book |chapter=Membrane Transport |first=William |last=Stillwell |title=An Introduction to Biological Membranes |date=April 26, 2013 |pages=305–337 |doi=10.1016/B978-0-444-52153-8.00014-3 |pmc=7182113 |isbn=978-0-444-52153-8 }}</ref> Cell surface receptors in the membrane allow cells to detect external signaling molecules such as hormones.<ref name="Guyton Hall 2016">{{cite book |last1=Guyton |first1=Arthur C. |last2=Hall |first2=John E. |year=2016 |title=Guyton and Hall Textbook of Medical Physiology |location=Philadelphia |publisher=Elsevier Saunders |pages=930–937 |url=https://books.google.com/books?id=3sWNCgAAQBAJ |oclc=1027900365 |isbn=978-1-4557-7005-2}}</ref>
===Cytoplasm=== {{Main|Cytoplasm}} The cell membrane encloses the cytoplasm of the cell that surrounds all of the cell's organelles.<ref name="Alberts2015"/> It is made up of two main components, the cytoskeleton made up of protein filaments, and the cytosol.<ref name="Alberts2015">{{cite book |last1=Alberts |first1=Bruce |title=Molecular biology of the cell |date=2015 |publisher=Garland science, Taylor and Francis group |location=New York |isbn=978-0-8153-4464-3 |page=642 |edition=6th}}</ref> The network of filaments and microtubules of the cytoskeleton gives shape and support to the cell, and has a part in organising the cell components.
The cytosol is a gel-like substance made up of water, ions, and non-essential biomolecules, and is the main site of protein synthesis, and degradation.<ref name="Alberts2015"/> The acidity (pH) of the cytosol is near neutral, and is regulated by transporters in the cell membrane. Different proteins in the cytoplasm operate optimally at different pHs.<ref name="Alberts2015c">{{cite book |last1=Alberts |first1=Bruce |title=Molecular biology of the cell |date=2015 |publisher=Garland science, Taylor and Francis group |location=New York |isbn=978-0-8153-4464-3 |page=604 |edition=6th}}</ref> The cytosol forms {{Val|30|-|50|u=%}} of the cell's volume.<ref>{{cite book |chapter=Metastable mesoscopic phases in concentrated protein solutions |display-authors=1 |first1=P. G. |last1=Vekilov |first2=W. |last2=Pan |first3=O. |last3=Gliko |first4=P. |last4=Katsonis |first5=O. |last5=Galkin |title=Aspects of Physical Biology: Biological Water, Protein Solutions, Transport and Replication |volume=752 |series=Lecture Notes in Physics |editor1-first=Giancarlo |editor1-last=Franzese |editor2-first=Miguel |editor2-last=Rubi |publisher=Springer Science & Business Media |year=2008 |isbn=978-3-540-78764-8 |pages=65–66 |chapter-url=https://books.google.com/books?id=d-aTnmKpaDQC&pg=PA65 }}</ref>
===Cytoskeleton=== {{Main|Cytoskeleton}} The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, and in the uptake of external materials by a cell.The cytoskeleton is composed of microtubules, intermediate filaments and microfilaments. There are a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments. The outermost part of the cytoskeleton is the cell cortex, or actin cortex, a thin layer of cross-linked actomyosins.<ref name="Zhu2024" /> Its thickness varies with cell type and physiology.<ref name="Zhu2024" /> It directs the transport through the ER and the Golgi apparatus.<ref>{{cite journal |title=Connecting the Cytoskeleton to the Endoplasmic Reticulum and Golgi |display-authors=1 |first1=Pinar S. |last1=Gurel |first2=Anna L. |last2=Hatch |first3=Henry N. |last3=Higgs |journal=Current Biology |volume=24 |issue=14 |pages=R660–R672 |date=July 21, 2014 |doi=10.1016/j.biochi.2015.03.021 |pmid=25869000 |pmc=4678951 }}</ref> The cytoskeleton in the animal cell also plays a part in cytokinesis, in the formation of the spindle apparatus during cell division, the separation of daughter cells.
===Organelles=== {{main|Organelle}}
Organelles are compartments of the cell that are specialized for carrying out one or more functions, analogous to the organs, such as the heart, and lungs.<ref name="NCBI"/> There are several types of organelles held in the cytoplasm. Most organelles are membrane-bound, and vary in size and number based on the growth of the host cell.<ref>{{cite journal |title=Scaling of Subcellular Structures |first=Wallace F. |last=Marshall |journal=Annual Review of Cell and Developmental Biology |volume=36 |pages=219–236 |year=2020 |doi=10.1146/annurev-cellbio-020520-113246 |pmid=32603615 |pmc=8562892 }}</ref> Organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, vesicles, and vacuoles. Membrane-less organelles include the nucleolus in the nucleus, centrosomes, ribosomes, proteasomes,<ref name="do Amaral2022">{{cite journal |vauthors=do Amaral MJ, de Andrade Rosa I, Andrade SA, Fang X, Andrade LR, Costa ML, Mermelstein C |title=The perinuclear region concentrates disordered proteins with predicted phase separation distributed in a 3D network of cytoskeletal filaments and organelles |journal=Biochim Biophys Acta Mol Cell Res |volume=1869 |issue=1 |article-number=119161 |date=January 2022 |pmid=34655689 |pmc=9385405 |doi=10.1016/j.bbamcr.2021.119161 |url=}}</ref><ref name="libre6">{{cite web |title=5.6: Cell Organelles |url=https://bio.libretexts.org/Bookshelves/Human_Biology/Human_Biology_(Wakim_and_Grewal)/05%3A_Cells/5.06%3A_Cell_Organelles |website=Biology LibreTexts |access-date=3 November 2025 |language=en |date=21 December 2018}}</ref> and vaults.<ref name="Muñoz-Juan2019"/>
===Nucleus=== {{Main|Cell nucleus}} [[Image:Diagram human cell nucleus multilang.svg|thumb|right|Diagram of the nucleus showing the ribosome-studded outer nuclear membrane, nuclear pores, DNA (complexed as chromatin), and the nucleolus.]] [[File:DNA structure infographic-5.svg|thumb|Diagram of DNA structure]] The cell nucleus is the largest organelle in the animal cell.<ref name="Khan2025">{{cite journal |last1=Khan |first1=Yusuf S. |last2=Farhana |first2=Aisha |title=Histology, Cell |url=https://www.ncbi.nlm.nih.gov/books/NBK554382/ |website=StatPearls |publisher=StatPearls Publishing |access-date=15 October 2025 |date=2025 |pmid=32119269 }}</ref> It houses the cell's chromosomes, and is the place where almost all DNA replication and RNA synthesis (transcription) occur. The nucleus is spherical and separated from the cytoplasm by a double-membraned nuclear envelope. A space between the membranes is called the perinuclear space. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called messenger RNA (mRNA). This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. The nucleolus is a specialized biomolecular condensate within the nucleus where ribosome subunits are assembled. It is one of several types of membrane-less nuclear bodies.<ref name="NCBI"/> Cells use DNA for their long-term information storage that is encoded in its DNA sequence.<ref name="NCBI"/> RNA is used for information transport (e.g., mRNA) and enzymatic functions (e.g., ribosomal RNA). Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.<ref name=Colville_Bassert_2015/>
The DNA of each cell is its genetic material, and is organized in multiple linear molecules, called chromosomes, that are coiled around histone proteins and housed in the cell nucleus.<ref name="visiblebody" /><ref>{{Cite web |author=Visible Body, part of Cengage Learning |title=Eukaryotic vs. Prokaryotic Chromosomes |url=https://www.visiblebody.com/learn/biology/dna-chromosomes/eukaryotic-vs-prokaryotic |access-date=2025-09-11 |website=www.visiblebody.com |language=en}}</ref> In humans, the nuclear genome is divided into 46 linear chromosomes, including 22 homologous chromosome pairs and a pair of sex chromosomes. The nucleus is a membrane-bound organelle.<ref>{{cite journal |title=Origin and evolution of metabolic sub-cellular compartmentalization in eukaryotes |first1=Toni |last1=Gabaldón |first2=Alexandros A. |last2=Pittis |journal=Biochimie |volume=119 |year=2015 |pages=262–268 |doi=10.1016/j.biochi.2015.03.021 |pmid=25869000 |pmc=4678951 }}</ref>
===Endoplasmic reticulum=== {{Main|Endoplasmic reticulum}} The endoplasmic reticulum (ER) is a transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that float freely in the cytoplasm. The ER has two forms: the rough endoplasmic reticulum (RER), which has ribosomes on its surface that secrete proteins into the ER, and the smooth endoplasmic reticulum (SER), which lacks ribosomes.<ref name="NCBI"/> The smooth ER plays a role in calcium sequestration and release, and helps in synthesis of lipid.<ref>{{cite book |chapter=Smooth Endoplasmic Reticulum |title=Functional Ultrastructure |pages=42–43 |last1=Pavelka |first1=M. |last2=Roth |first2=J. |year=2010 |publisher=Springer |location=Vienna |doi=10.1007/978-3-211-99390-3_23 |isbn=978-3-211-99389-7 }}</ref>
===Golgi apparatus=== {{Main|Golgi apparatus}} The Golgi apparatus processes and packages proteins, and lipids, that are synthesized by the cell. It is organized as a stack of plate-like structures known as cisternae.<ref>{{cite journal |title=The Golgi apparatus |first1=Ben |last1=Short |first2=Francis A. |last2=Barr |journal=Current Biology |volume=10 |issue=16 |pages=R583–R585 |date=August 14, 2000 |doi=10.1016/S0960-9822(00)00644-8 |pmid=10985372 |bibcode=2000CBio...10.R583S }}</ref>
===Mitochondria=== {{Main|Mitochondrion}} Mitochondria are self-replicating double membrane-bound organelles that occur in various numbers, shapes, and sizes in the cytoplasm of the cell.<ref name="NCBI"/> Aerobic respiration in the mitochondria generates the cell's energy by oxidative phosphorylation, using oxygen to release energy stored in cellular nutrients (typically pertaining to glucose) to generate adenosine triphosphate (ATP).<ref>{{cite journal |title=A Biophysical Model of the Mitochondrial Respiratory System and Oxidative Phosphorylation |first=Daniel A. |last=Beard |journal=PLOS Computational Biology |date=September 9, 2005 |volume=1 |issue=4 |article-number=e36 |doi=10.1371/journal.pcbi.0010036 |pmid=16163394 |pmc=1201326 |bibcode=2005PLSCB...1...36B |doi-access=free }}</ref> Mitochondria are descended from bacteria that formed an endosymbiotic relationship with ancient prokaryotes.<ref>{{Cite magazine |magazine=Knowable Magazine |last=Callier |first=Viviane |date=2022-06-08 |title=Mitochondria and the origin of eukaryotes |doi=10.1146/knowable-060822-2 }}</ref> Mitochondria multiply by binary fission<ref>{{cite book |title=Molecular Biology of Assemblies and Machines |display-authors=1 |first1=Alasdair |last1=Steven |first2=Wolfgang |last2=Baumeister |first3=Louise N. |last3=Johnson |first4=Richard N. |last4=Perham |publisher=Garland Science, Taylor & Francis Group |year=2016 |isbn=978-1-134-98282-0 |url=https://books.google.com/books?id=8QSoCwAAQBAJ&pg=PT110 }}</ref> and have their own DNA contained in multiple small circular chromosomes.<ref name="González-Arzola">{{cite journal |vauthors=González-Arzola K, Díaz-Quintana A |title=Mitochondrial Factors in the Cell Nucleus |journal=Int J Mol Sci |volume=24 |issue=17 |date=September 2023 |article-number=13656 |pmid=37686461 |pmc=10563088 |doi=10.3390/ijms241713656 |doi-access=free |url=}}</ref><ref>{{cite journal |title=Why chloroplasts and mitochondria contain genomes |first=John F. |last=Allen |journal=Comparative and Functional Genomics |date=February 14, 2003 |volume=4 |issue=1 |pages=31–36 |doi=10.1002/cfg.245 |pmc=2447392 |pmid=18629105 }}</ref> The mitochondrial DNA (mtDNA) is very small compared to nuclear DNA,<ref name="NCBI" /> but it codes for 13 proteins involved in mitochondrial energy production and specific transfer RNAs (tRNAs).<ref>{{cite journal |title=Animal mitochondrial genomes Open Access |first=Jeffrey L. |last=Boore |journal=Nucleic Acids Research |volume=27 |issue=8 |date=April 1999 |pages=1767–1780 |doi=10.1093/nar/27.8.1767 |pmid=10101183 |pmc=148383 }}</ref> Mitochondria also have their own ribosomes known as mitoribosomes.<ref name="Greber">{{cite journal |vauthors=Greber BJ, Ban N |title=Structure and Function of the Mitochondrial Ribosome |journal=Annu Rev Biochem |volume=85 |issue= |pages=103–32 |date=June 2016 |pmid=27023846 |doi=10.1146/annurev-biochem-060815-014343 |url=}}</ref>
===Lysosomes=== {{Main|Lysosome}} A lysosome is the most acidic compartment in the cell.<ref name="genome">{{cite web |title=Lysosome |url=https://www.genome.gov/genetics-glossary/Lysosome |website=www.genome.gov |access-date=19 December 2025 |language=en}}</ref> It contains over 60 different hydrolytic enzymes that need an acidic environment.<ref name="Feng">{{cite journal |vauthors=Feng X, Liu S, Xu H |title=Not just protons: Chloride also activates lysosomal acidic hydrolases |journal=J Cell Biol |volume=222 |issue=6 |date=June 2023 |article-number=e202305007 |pmid=37191899 |pmc=10191866 |doi=10.1083/jcb.202305007 |url=}}</ref> They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. The cell could not house these destructive enzymes if they were not contained in a membrane-bound compartment.<ref name="NCBI"/><ref>{{cite book |chapter=Peroxisomes and Lysosomes |display-authors=1 |first1=Ubaldo |last1=Soto |first2=Stephan |last2=Rapp |first3=Karin |last3=Gorgas |first4=Wilhelm W. |last4=Just |title=Molecular & Cell Biology of the Liver |editor-first=Albert V. |editor-last=LeBouton |publisher=CRC Press |year=1993 |isbn=978-0-8493-8891-0 |pages=181–211 |chapter-url=https://books.google.com/books?id=4Hk2z7C2xKUC&pg=PA181 }}</ref>
===Peroxisomes=== {{Main|Peroxisome}} Peroxisomes are microbodies bounded by a single membrane. A peroxisome has no DNA or ribosomes and the proteins that it needs are encoded in the nucleus, and selectively imported from the cytosol. Some proteins enter via the endomembrane reticulum.<ref name="Albertsa2015">{{cite book |last1=Alberts |first1=Bruce |title=Molecular biology of the cell |date=2015 |publisher=Garland science, Taylor and Francis group |location=New York |isbn=978-0-8153-4464-3 |pages=666–667 |edition=6th}}</ref> They have enzymes that rid the cell of toxic peroxides. The enzymatic content of the peroxisomes varies widely across the species, as it can in an individual organism.<ref name="Gabaldon2010">{{cite journal |vauthors=Gabaldón T |title=Peroxisome diversity and evolution |journal=Philos Trans R Soc Lond B Biol Sci |volume=365 |issue=1541 |pages=765–73 |date=March 2010 |pmid=20124343 |pmc=2817229 |doi=10.1098/rstb.2009.0240 |url=}}</ref><ref name="Albertsa2015"/> The peroxisomes in animal cells are concentrated in the liver cells and adipocytes.<ref name="Gabaldon2010"/>
===Vacuoles=== {{Main|Vacuole}} Vacuoles sequester waste products. Some cells, most notably ''Amoeba'', have contractile vacuoles, which can pump water out of the cell if there is too much water.<ref>{{Cite journal |last1=Pappas |first1=George D. |last2=Brandt |first2=Philip W. |date=1958 |title=The Fine Structure of the Contractile Vacuole in Ameba |journal=The Journal of Biophysical and Biochemical Cytology |volume=4 |issue=4 |pages=485–488 |doi=10.1083/jcb.4.4.485 |jstor=1603216 |pmid=13563556 |pmc=2224495 |issn=0095-9901 }}</ref>
===Centrosome=== {{Main|Centrosome}} The centrosome is a membrane-less organelle composed of pericentriolar material and the two centrioles.<ref name="Genome2025a">{{cite web |title=Centriole |url=https://www.genome.gov/genetics-glossary/Centriole |website=www.genome.gov |access-date=30 October 2025 |language=en}}</ref><ref name="libre6"/> The centrosome is the main microtubule organizing center in the animal cell that produces the microtubules key components of the cytoskeleton. Centrosomes are composed of two centrioles which lie perpendicular to each other in which each has an organization like a cartwheel, which separate during cell division and help in the formation of the mitotic spindle.<ref name=Prigent_Uzbekov_2022>{{cite journal |title=Duplication and Segregation of Centrosomes during Cell Division |first1=Claude |last1=Prigent |first2=Rustem |last2=Uzbekov |journal=Cells |year=2022 |volume=11 |issue=15 |article-number=2445 |doi=10.3390/cells11152445 |pmid=35954289 |pmc=9367774 |doi-access=free }}</ref>
===Ribosomes=== {{Main|Ribosome}} A ribosome is a large complex of RNA and protein molecules considered as a membrane-less organelle when freely found in the cytosol, or as a membrane-bound organelle when located in the rough type of endoplasmic reticulum.<ref>{{cite book | vauthors = Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P | chapter = Membrane-bound Ribosomes Define the Rough ER | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK26841/#A2204 | title = Molecular Biology of the Cell | edition = 4th | location = New York | publisher = Garland Science | date = 2002 | isbn = 978-0-8153-4072-0 }}</ref><ref name="NCBI"/> They each consist of two subunits, one larger than the other, and act as an assembly line where messenger RNA from the nucleus is used to synthesise proteins from amino acids.<ref name="NCBI"/>
===Vaults=== {{Main|Vault (organelle)}} A vault is a large ribonuclear protein particle, a membrane-less organelle, three times the size of a ribosome but with only three proteins in contrast to the near hundred in the ribosome.<ref name="Muñoz-Juan2019">{{cite journal |vauthors=Muñoz-Juan A, Carreño A, Mendoza R, Corchero JL |title=Latest Advances in the Development of Eukaryotic Vaults as Targeted Drug Delivery Systems |journal=Pharmaceutics |volume=11 |issue=7 |date=June 2019 |page=300 |pmid=31261673 |pmc=6680493 |doi=10.3390/pharmaceutics11070300 |doi-access=free |url=}}</ref> Most human cells have around 10,000 vaults, and in some types of immune cell there may be up to 100,000. Macrophages have the greatest number of vaults of any human cell.<ref name="Science2024">{{cite web |title=This biologist aims to solve the cell's biggest mystery. Could it help cancer patients, too? |url=https://www.science.org/content/article/biologist-aims-solve-cell-s-biggest-mystery-could-it-help-cancer-patients-too |website=www.science.org |access-date=20 November 2025 |language=en}}</ref> Vaults are largely overlooked because their functions are purely speculative. They may play a role in transport from the nucleus to the cytoplasm, and may serve as scaffolds for signal transduction proteins. They are present in normal tissues, and more so in secretory and excretory epithelial cells.<ref name="Muñoz-Juan2019"/><ref name="Science2024"/>
===Proteasome=== {{Main|Proteasome}}{{See also|Intramembrane protease}} Proteasomes are intricate membrane-less protein complexes responsible for the degradation of regulatory proteins, and damaged proteins in the cytosol and nucleus. They also function in protein homeostasis, stress response, and in the control of cell division and signal transduction.<ref name="Bard2018">{{cite journal |vauthors=Bard JA, Goodall EA, Greene ER, Jonsson E, Dong KC, Martin A |title=Structure and Function of the 26S Proteasome |journal=Annu Rev Biochem |volume=87 |issue= 1|pages=697–724 |date=June 2018 |pmid=29652515 |pmc=6422034 |doi=10.1146/annurev-biochem-062917-011931 |bibcode=2018ARBio..87..697B |url=}}</ref>
===Animal cell types=== {{See also|Cell type}} [[File:Cells from different germ layers.webp|thumb|upright=1.2|Cells that arise from the three germ layers]] Some types of specialized cell are localized to a particular animal group. Vertebrates for example have specialized, structurally changed cells including muscle cells. The cell membrane of a skeletal muscle cell or of a cardiac muscle cell is termed the sarcolemma.<ref name="Roberts2020">{{cite journal |last1=Roberts |first1=MD |last2=Haun |first2=CT |last3=Vann |first3=CG |last4=Osburn |first4=SC |last5=Young |first5=KC |title=Sarcoplasmic Hypertrophy in Skeletal Muscle: A Scientific "Unicorn" or Resistance Training Adaptation? |journal=Frontiers in Physiology |date=2020 |volume=11 |article-number=816 |doi=10.3389/fphys.2020.00816 |doi-access=free |pmid=32760293 |pmc=7372125 }}</ref> And the cytoplasm is termed the sarcoplasm. Skeletal muscle cells also become multinucleated. Populations of animal groups evolve to become distinct species, where sexual reproduction is isolated. The many species of vertebrates for example have other unique characteristics by way of additional specialized cells. In some species of electric fish for example modified muscle cells or nerve cells have specialized to become electerocytes capable of creating and storing electrical energy for future release, as in stunning prey, or use in electrolocation.<ref name="Markham2013">{{cite journal |vauthors=Markham MR |title=Electrocyte physiology: 50 years later |journal=J Exp Biol |volume=216 |issue=Pt 13 |pages=2451–8 |date=July 2013 |pmid=23761470 |doi=10.1242/jeb.082628 |bibcode=2013JExpB.216.2451M |url=}}</ref> These are large flat cells in the electric eel, and electric ray in which thousands are stacked into an electric organ comparable to a voltaic pile.<ref name="Mauro">{{cite journal |vauthors=Mauro A |title=The role of the Voltaic pile in the Galvani-Volta controversy concerning animal vs. metallic electricity |journal=J Hist Med Allied Sci |volume=24 |issue=2 |pages=140–50 |date=April 1969 |pmid=4895861 |doi=10.1093/jhmas/xxiv.2.140 |url=}}</ref>
Many animal cells are ciliated and most cells except red blood cells have primary cilia. Primary cilia play important roles in chemosensation and mechanosensation.<ref>{{Citation |last1=Haycraft |first1=Courtney J. |title=Chapter 11 Cilia Involvement in Patterning and Maintenance of the Skeleton |date=2008-01-01 |journal=Current Topics in Developmental Biology |volume=85 |pages=303–332 |series=Ciliary Function in Mammalian Development |publisher=Academic Press |doi=10.1016/s0070-2153(08)00811-9 |last2=Serra |first2=Rosa |pmid=19147010 |pmc=3107512 |isbn=978-0-12-374453-1 }}</ref><ref name="Zhang 2013">{{Cite journal |last1=Zhang |first1=Qing |last2=Hu |first2=Jinghua |last3=Ling |first3=Kun |date=2013-09-10 |title=Molecular views of Arf-like small GTPases in cilia and ciliopathies |journal=Experimental Cell Research |series=Special Issue: Small GTPases |volume=319 |issue=15 |pages=2316–2322 |doi=10.1016/j.yexcr.2013.03.024 |issn=0014-4827 |pmc=3742637 |pmid=23548655}}</ref> Each cilium may be "viewed as a sensory cellular antennae that coordinates a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."<ref name="Christenson2008">{{cite journal |last1=Satir |first1=P. |last2=Christensen |first2=Søren T. |title=Structure and function of mammalian cilia |journal=Histochemistry and Cell Biology |volume=129 |issue=6 |pages=687–693 |date=June 2008 |pmid=18365235 |pmc=2386530 |doi=10.1007/s00418-008-0416-9 |id=1432-119X }}</ref> The cilia in other cells are motile organelles, and in the respiratory epithelium play an important role in the movement of mucus. In the reproductive system ciliated epithelium in the fallopian tubes move the egg from the uterus to the ovary. Motile cilia also known as flagella, drive the sperm cells.<ref name="Petriman2020">{{cite journal |vauthors=Petriman NA, Lorentzen E |title=Structural insights into the architecture and assembly of eukaryotic flagella |journal=Microb Cell |volume=7 |issue=11 |pages=289–299 |date=September 2020 |pmid=33150161 |pmc=7590530 |doi=10.15698/mic2020.11.734 |url=}}</ref> Invertebrate planarians have ciliated excretory flame cells.<ref name="libre4">{{cite web |title=41.8: Excretion Systems - Flame Cells of Planaria and Nephridia of Worms |url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/41%3A_Osmotic_Regulation_and_the_Excretory_System/41.08%3A_Excretion_Systems_-_Flame_Cells_of_Planaria_and_Nephridia_of_Worms |website=Biology LibreTexts |access-date=18 October 2025 |language=en |date=17 July 2018}}</ref> Other excretory cells also found in planarians are solenocytes that are long and flagellated.
== Plant cells == {{Main|Plant cell}}
[[File:Plant cell structure-en.svg|thumb|upright=1.2|Structure of a typical plant cell ]]
[[File:Wilson1900Fig2.jpg|thumb|upright=1.2|Onion (''Allium cepa'') root cells in different phases of the cell cycle (drawn by E.B. Wilson, 1900)]]
Plant cells have cell walls composed of cellulose, hemicelluloses, and pectin that are constructed outside the cell membrane. In sclerenchyma tissue lignin is secreted to form a secondary wall inside the primary cell wall.<ref name="Libre2026">{{cite web |title=6.1: Plant Cells and Tissues |url=https://bio.libretexts.org/Bookshelves/Botany/The_Science_of_Plants_-_Understanding_Plants_and_How_They_Grow_(Michaels_et_al.)/06%3A_Cells_Tissues_and_Woody_Growth/6.01%3A_Plant_Cells_and_Tissues |website=Biology LibreTexts |access-date=7 March 2026 |language=en |date=26 July 2022}}</ref> Cutin is secreted outside the primary cell wall and into the outer layers of the secondary cell wall of the epidermal cells of leaves, stems and other above-ground organs to form the plant cuticle.{{Fact|date=March 2026}} Cell walls perform many essential functions, they provide shape to form the tissue and organs of the plant, and play an important role in intercellular communication and plant-microbe interactions.{{Fact|date=March 2026}} Specialized cell-to-cell communication pathways known as plasmodesmata, occur in the form of pores in the primary cell wall through which the cell membrane and endoplasmic reticulum of adjacent cells are continuous.{{Fact|date=March 2026}}
Organelles in plant cells, include pigment-containing plastids, especially chloroplasts that contain chlorophyll (also found in algae), large water-storage vacuoles, and two types of peroxisome. Chloroplasts capture the sun's energy to make carbohydrates through photosynthesis.<ref>{{cite journal |title=The evolution of photosynthesis and chloroplasts |first1=Lars Olof |last1=Björn |author2=Govindjee |journal=Current Science |date=2009 |volume=96 |issue=11 June 10, 2009 |pages=1466–1474 |jstor=24104775 }}</ref> Chromoplasts contain fat-soluble carotenoid pigments such as orange carotene and yellow xanthophylls which helps in synthesis and storage. Leucoplasts are non-pigmented plastids and helps in storage of nutrients.<ref>{{cite book |last=Sato |first=N. |year=2006 |pages=75–102 |title=The Structure and Function of Plastids |volume=23 |editor1=Wise, R. R. |editor2=Hoober, J. K. |publisher=Springer |chapter=Origin and Evolution of Plastids: Genomic View on the Unification and Diversity of Plastids |isbn=978-1-4020-4060-3 |doi=10.1007/978-1-4020-4061-0_4 |series=Advances in Photosynthesis and Respiration}}</ref> Plastids divide by binary fission.<ref name="Pyke">{{cite journal |last1=Pyke |first1=KA |title=Plastid division. |journal=AoB Plants |date=2010 |volume=2010 |article-number=plq016 |doi=10.1093/aobpla/plq016 |pmid=22476074|pmc=2995336 }}</ref> The vacuoles are larger than those in animal cells, and their membrane transports ions against concentration gradients.<ref>{{cite journal |title=In and out of the plant storage vacuole |display-authors=1 |first1=Ed |last1=Etxeberria |first2=Javier |last2=Pozueta-Romero |first3=Pedro |last3=Gonzalez |journal=Plant Science |volume=190 |date=July 2012 |pages=52–61 |doi=10.1016/j.plantsci.2012.03.010 |pmid=22608519 |bibcode=2012PlnSc.190...52E }}</ref> <ref name=Lew_Fitzgerald_2021>{{cite book |title=Plant Cells |edition=Third |first1=Kristi |last1=Lew |first2=Brad |last2=Fitzpatrick |publisher=Infobase Holdings, Inc |year=2021 |isbn=978-1-64693-728-8 |pages=14–16 |url=https://books.google.com/books?id=ttyPEAAAQBAJ&pg=PA14 }}</ref> One type of peroxisome is in the leaves where it takes part in photorespiration. The other type is in germinating seeds where it takes part in the conversion of fatty acids into sugars for the plant's growth.<ref name="Albertsa2015"/> In this peroxisome type the enzymatic content is so different from other groups that it has an alternative name of glyoxysome. The enzymes are of the glyoxylate cycle.<ref name="Gabaldon2010"/>
The plant cytoskeleton is a dynamic structure that has a scaffold of microtubules and microfilaments, but no intermediate filaments.<ref name="Takemoto">{{cite journal |vauthors=Takemoto D, Hardham AR |title=The cytoskeleton as a regulator and target of biotic interactions in plants |journal=Plant Physiol |volume=136 |issue=4 |pages=3864–76 |date=December 2004 |pmid=15591444 |pmc=535820 |doi=10.1104/pp.104.052159 |url=}}</ref> The microtubule organizing center in plant cells is often sited underneath the cell membrane where nucleated microtubules often form sheet-like semi-parallel arrays.<ref name="Wu2017">{{cite journal |last1=Wu |first1=Jingchao |last2=Akhmanova |first2=Anna |title=Microtubule-Organizing Centers |journal=Annual Review of Cell and Developmental Biology |date=6 October 2017 |volume=33 |pages=51–75 |doi=10.1146/annurev-cellbio-100616-060615 |pmid=28645217 |hdl=1874/359425 |hdl-access=free }}</ref>
Plant hormones are produced by all plant cells. Different hormones act as signaling molecules to control all aspects of the plant's growth and development including embryogenesis and reproduction, and in pathogen defense.<ref>{{cite journal | vauthors = Méndez-Hernández HA, Ledezma-Rodríguez M, Avilez-Montalvo RN, Juárez-Gómez YL, Skeete A, Avilez-Montalvo J, De-la-Peña C, Loyola-Vargas VM | display-authors = 6 | title = Signaling Overview of Plant Somatic Embryogenesis | journal = Frontiers in Plant Science | volume = 10 | article-number = 77 | date = 2019 | pmid = 30792725 | pmc = 6375091 | doi = 10.3389/fpls.2019.00077 | doi-access = free | bibcode = 2019FrPS...10...77M }}</ref><ref>{{cite journal | vauthors = Shigenaga AM, Argueso CT | title = No hormone to rule them all: Interactions of plant hormones during the responses of plants to pathogens | journal = Seminars in Cell & Developmental Biology | volume = 56 | pages = 174–189 | date = August 2016 | pmid = 27312082 | doi = 10.1016/j.semcdb.2016.06.005 }}</ref><ref>{{cite journal | vauthors = Bürger M, Chory J | title = Stressed Out About Hormones: How Plants Orchestrate Immunity | journal = Cell Host & Microbe | volume = 26 | issue = 2 | pages = 163–172 | date = August 2019 | pmid = 31415749 | doi = 10.1016/j.chom.2019.07.006 | pmc = 7228804 }}</ref>
==Algal cells== Algae members are photoautotrophs able to use photosynthesis to produce energy. In eukaryotes, photosynthesis is made possible by the use of plastids, organelles in the cytoplasm known as chloroplasts.
Photosynthesis is found in both prokaryotic cyanobacteria and multiple clades of eukaryotic algae; red algae, brown algae, and green algae, which are closely related to land plants.<ref>{{Citation |last=Raven |first=John A. |title=Carbon |date=2012 |work=Ecology of Cyanobacteria II |pages=443–460 |editor-last=Whitton |editor-first=Brian A. |url=https://link.springer.com/10.1007/978-94-007-3855-3_17 |access-date=2026-05-05 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-007-3855-3_17 |isbn=978-94-007-3854-6|url-access=subscription }}.</ref><ref>{{cite journal |last1=Yoon |first1=Hwan Su |last2=Hackett |first2=Jeremiah D. |last3=Ciniglia |first3=Claudia |last4=Pinto |first4=Gabriele |last5=Bhattacharya |first5=Debashish |title=A Molecular Timeline for the Origin of Photosynthetic Eukaryotes |journal=Molecular Biology and Evolution |date=May 2004 |volume=21 |issue=5 |pages=809–818 |doi=10.1093/molbev/msh075 |pmid=14963099 |doi-access=free}}</ref>
Alginate is a polysaccharide found in the matrix of the cell walls of brown algae, and has many important uses in the food industry, and in pharmacology.<ref name="Abka-Khajouei">{{cite journal |vauthors=Abka-Khajouei R, Tounsi L, Shahabi N, Patel AK, Abdelkafi S, Michaud P |title=Structures, Properties and Applications of Alginates |journal=Mar Drugs |volume=20 |issue=6 |date=May 2022 |page=364 |pmid=35736167 |pmc=9225620 |doi=10.3390/md20060364 |bibcode=2022MarDr..20..364A |doi-access=free |url=}}</ref>
== Fungal cells == {{Main|Fungus}}
The cells of fungi have in addition to the shared eukaryotic organelles a spitzenkörper in their endomembrane system, associated with hyphal tip growth. It is a phase-dark body that is composed of an aggregation of membrane-bound vesicles containing cell wall components, serving as a point of assemblage and release of such components intermediate between the Golgi and the cell membrane. The spitzenkörper is motile and generates new hyphal tip growth as it moves forward.<ref name=Steinberg>{{cite journal |vauthors = Steinberg G |title = Hyphal growth: a tale of motors, lipids, and the Spitzenkörper |journal = Eukaryotic Cell |volume = 6 |issue = 3 |pages = 351–60 |date = March 2007 |pmid = 17259546 |pmc = 1828937 |doi = 10.1128/EC.00381-06 |bibcode = 2007EukC....6..351S }}</ref>
The cell walls of fungi are uniquely made of a chitin-glucan complex.<ref name="Gow 2017">{{cite journal |last1=Gow |first1=Neil A. R. |last2=Latge |first2=Jean-Paul |last3=Munro |first3=Carol A. |last4=Heitman |first4=Joseph |title=The fungal cell wall: Structure, biosynthesis, and function |journal=Microbiology Spectrum |volume=5 |issue=3 |year=2017 |article-number=5.3.01 |doi=10.1128/microbiolspec.FUNK-0035-2016 |pmid=28513415 |pmc=11687499 |hdl=2164/8941 |s2cid=5026076 |hdl-access=free}}</ref> Chloroplasts are not found in fungal cells, their pigments are instead associated with their cell walls.<ref name="biolibre2026">{{cite web |title=24.1B: Fungi Cell Structure and Function |url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/24%3A_Fungi/24.01%3A_Characteristics_of_Fungi/24.1B%3A_Fungi_Cell_Structure_and_Function#:~:text=Unlike%20plant%20cells%2C%20fungal%20cells%20do%20not%20have%20chloroplasts%20or%20chlorophyll. |website=Biology LibreTexts |access-date=10 May 2026 |language=en |date=15 July 2018}}</ref>
== Protist cells == {{Further|Protist#Common types}} The cells of protists may be bounded only by a cell membrane, or may in addition have a cell wall, or may be covered by a pellicle (in ciliates), a test (in testate amoebae), or a frustule (in diatoms).
Some protists such as amoebae may feed on other organisms and ingest food by phagocytosis. Vacuoles known as phagosomes in the cytoplasm may be used to draw in and incorporate the captured particles. Other types of protists are photoautotrophs, providing themselves with energy by photosynthesis.<ref name="libre5">{{cite web |title=8.16E: Cell Structure, Metabolism, and Motility |url=https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/08%3A_Microbial_Evolution_Phylogeny_and_Diversity/8.16%3A_Eukaryotic_Microbial_Diversity/8.16E%3A_Cell_Structure_Metabolism_and_Motility |website=Biology LibreTexts |access-date=14 October 2025 |language=en |date=23 June 2017}}</ref> Most single-celled protists are motile, and generate movement with cilia, flagella, or pseudopodia.<ref name="biolibre"/>
Ciliates have two different sorts of nuclei: a tiny, diploid micronucleus (the "generative nucleus", which carries the germline of the cell), and a large, ampliploid macronucleus (the "vegetative nucleus", which takes care of general cell regulation.<ref>{{Cite journal|last=Raikov|first=I.B.|date=1969|title=The Macronucleus of Ciliates|url=https://books.google.com/books?id=YBnLBAAAQBAJ&q=raikov+macronucleus&pg=PA1|journal=Research in Protozoology|volume=3|pages=4–115|isbn=978-1-4831-8614-6}}</ref><ref name="Archibald-2017">{{Cite book|url=https://www.springer.com/gp/book/9783319281476|title=Handbook of the Protists|date=2017|publisher=Springer International Publishing|isbn=978-3-319-28147-6|editor-last=Archibald|editor-first=John M.|edition=2|page=691|language=en|editor-last2=Simpson|editor-first2=Alastair G. B.|editor-last3=Slamovits|editor-first3=Claudio H.}}</ref>
== Cellular processes ==
{{See also|Cell cycle|Cell physiology}}
[[File:Three cell growth types.svg|thumb|upright=1.25|Prokaryotes divide by binary fission, while eukaryotes divide by mitosis or meiosis.]]
=== Replication ===
{{main|Cell division}}
[[File:HeLa cells stained with Hoechst 33258.jpg|thumb|Human cancer cells, specifically HeLa cells, with DNA stained blue. The central and rightmost cell are in interphase, so their DNA is diffuse and the entire nuclei are labelled. The cell on the left is going through mitosis and its chromosomes have condensed.]]
During cell division, a single cell, the ''mother cell'' divides into two daughter cells. This leads to the growth of tissue in multicellular organisms. Prokaryotic cells divide by binary fission, while eukaryotic cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell, called cytokinesis. A diploid cell may undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells.{{citation needed|date=November 2025}}
DNA replication, or the process of duplicating a cell's genome,<ref name="NCBI"/> always happens when a cell divides through mitosis or binary fission.{{citation needed|date=November 2025}} This occurs during the S (synthesis) phase of the cell cycle.<ref>{{Cite journal |last1=Takeda |first1=David Y. |last2=Dutta |first2=Anindya |date=April 2005 |title=DNA replication and progression through S phase |journal=Oncogene |language=en |volume=24 |issue=17 |pages=2827–2843 |doi=10.1038/sj.onc.1208616 |pmid=15838518 }}</ref>
In meiosis, the DNA is replicated only once, while the cell divides twice. DNA replication only occurs before meiosis I. DNA replication does not occur when the cells divide the second time, in meiosis II.<ref>{{cite book|title=Campbell Biology{{snd}}Concepts and Connections|year=2009|publisher=Pearson Education|page=138}}</ref> Replication, like all cellular activities, requires specialized proteins.<ref name="NCBI"/>
===Signaling=== {{main|Cell signaling}}
Cell signaling is the process by which a cell interacts with itself, other cells, and the environment. Typically, the signaling process involves three components: the first messenger (the ligand), the receptor, and the signal itself.<ref>{{Cite journal |display-authors=1 |last1=Nair |first1=Arathi |last2=Chauhan |first2=Prashant |last3=Saha |first3=Bhaskar |last4=Kubatzky |first4=Katharina F. |date=July 4, 2019 |title=Conceptual Evolution of Cell Signaling |journal=International Journal of Molecular Sciences |volume=20 |issue=13 |page=3292 |doi=10.3390/ijms20133292 |doi-access=free |issn=1422-0067 |pmc=6651758 |pmid=31277491 }}</ref> Most cell signaling is chemical in nature, and can occur with neighboring cells or more distant targets. Signal receptors are complex proteins or tightly bound multimer of proteins, located in the plasma membrane or within the interior.<ref name=Alberts_et_al_2002/>
Each cell is programmed to respond to specific extracellular signal molecules, and this process is the basis of development, tissue repair, immunity, and homeostasis. Individual cells are able to manage receptor sensitivity including turning them off, and receptors can become less sensitive when they are occupied for long durations.<ref name=Alberts_et_al_2002>{{cite book |display-authors=1 |last1=Alberts |first1=Bruce |last2=Johnson |first2=Alexander |last3=Lewis |first3=Julian |last4=Raff |first4=Martin |last5=Roberts |first5=Keith |last6=Walter |first6=Peter |title=Molecular Biology of the Cell |edition=4th |date=2002 |publisher=Garland Science |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK26813/ |chapter=General Principles of Cell Communication }}</ref> Errors in signaling interactions may cause diseases such as cancer, autoimmunity, and diabetes.<ref>{{cite web |title=How Dysregulated Cell Signaling Causes Disease |first=Deliana |last=Infante |website=News-Medical.Net |date=December 2, 2024 |url=https://www.news-medical.net/health/How-Dysregulated-Cell-Signaling-Causes-Disease.aspx |access-date=2025-10-05 }}</ref>
===Protein targeting=== {{Main|Protein targeting}} Protein targeting or protein sorting is the biological mechanism by which proteins are transported to their appropriate destinations within or outside the cell.<ref name="Nelson-2017">{{Cite book| vauthors = Nelson DL |title=Lehninger principles of biochemistry|others=Cox, Michael M.,, Lehninger, Albert L.| date=January 2017|isbn=978-1-4641-2611-6|edition=Seventh|location=New York, NY|oclc=986827885}}</ref><ref name="Lodish, Berk, Kaiser, Krieger, Bretscher, Ploegh, Martin, Yaffe, Amon-2021">{{Cite book |last=Lodish, Berk, Kaiser, Krieger, Bretscher, Ploegh, Martin, Yaffe, Amon |title=Molecular Cell Biology |publisher=W.H. Freeman and Company |year=2021 |isbn=978-1-319-20852-3 |edition=9th |location=New York, NY}}</ref> Proteins can be targeted to the inner space of an organelle, different intracellular membranes, the plasma membrane, or to the exterior of the cell via secretion.<ref name="Nelson-2017" /><ref name="Lodish, Berk, Kaiser, Krieger, Bretscher, Ploegh, Martin, Yaffe, Amon-2021" /> Information contained in the protein itself directs this delivery process.<ref name="Lodish, Berk, Kaiser, Krieger, Bretscher, Ploegh, Martin, Yaffe, Amon-2021" /><ref name="Blobel-1975">{{cite journal | vauthors = Blobel G, Dobberstein B | title = Transfer of proteins across membranes. I. Presence of proteolytically processed and unprocessed nascent immunoglobulin light chains on membrane-bound ribosomes of murine myeloma | journal = The Journal of Cell Biology | volume = 67 | issue = 3 | pages = 835–51 | date = December 1975 | pmid = 811671 | pmc = 2111658 | doi = 10.1083/jcb.67.3.835 }}</ref> Correct sorting is crucial for the cell; errors or dysfunction in sorting have been linked to multiple diseases.<ref name="Lodish, Berk, Kaiser, Krieger, Bretscher, Ploegh, Martin, Yaffe, Amon-2021" /><ref name="Protein sorting gone wrong--VPS10P">{{cite journal | vauthors = Schmidt V, Willnow TE | title = Protein sorting gone wrong--VPS10P domain receptors in cardiovascular and metabolic diseases | journal = Atherosclerosis | volume = 245 | pages = 194–9 | date = February 2016 | pmid = 26724530 | doi = 10.1016/j.atherosclerosis.2015.11.027 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Guo Y, Sirkis DW, Schekman R | title = Protein sorting at the trans-Golgi network | journal = Annual Review of Cell and Developmental Biology | volume = 30 | issue = 1 | pages = 169–206 | date = 2014-10-11 | pmid = 25150009 | doi = 10.1146/annurev-cellbio-100913-013012 }}</ref>
=== DNA repair ===
{{main|DNA repair}}
All cells contain enzyme systems that scan for DNA damage and carry out repair. Diverse repair processes have evolved in all organisms. Repair is vital to maintain DNA integrity, avoid cell death and errors of replication that could lead to mutation. Repair processes include nucleotide excision repair, DNA mismatch repair, non-homologous end joining of double-strand breaks, recombinational repair and light-dependent repair (photoreactivation).<ref>{{cite book |last1=Snustad |first1=D. Peter |last2=Simmons |first2=Michael J. |title=Principles of Genetics |publisher=John Wiley & Sons |year=2015 |edition=7th |chapter=DNA repair mechanisms |isbn=978-1-119-14228-7 |pages=333–336 |chapter-url=https://books.google.com/books?id=NBB0CgAAQBAJ&pg=PA333}}</ref>
=== Growth and metabolism ===
{{main|Cell growth|Metabolism|Photosynthesis}}
Between successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism, in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions.<ref name=Smolin_Grosvenor_2019>{{cite book |title=Nutrition: Science and Applications |first1=Lori A. |last1=Smolin |first2=Mary B. |last2=Grosvenor |edition=4 |publisher=John Wiley & Sons |year=2019 |isbn=978-1-119-49527-7 |pages=99–100 |url=https://books.google.com/books?id=VSaVDwAAQBAJ&pg=PA99 }}</ref>
Complex sugars can be broken down into simpler sugar molecules called monosaccharides such as glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP),<ref name="NCBI"/> a molecule that possesses readily available energy, through two different pathways. In plant cells, chloroplasts create sugars by photosynthesis, using the energy of light to join molecules of water and carbon dioxide.<ref>{{cite book |chapter=Chloroplasts and Photosynthesis |display-authors=1 |last1=Alberts |first1=B. |last2=Johnson |first2=A. |last3=Lewis |first3=J. |last4=Raff |first4=M. |last5=Roberts |first5=K. |last6=Walter |first6=P. |title=Molecular Biology of the Cell |edition=4th |location=New York |publisher=Garland Science |year=2002 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK26819/ |access-date=2025-10-04 }}</ref>
=== Protein synthesis ===
{{main|Protein biosynthesis}}
Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps: transcription and translation.<ref name=Colville_Bassert_2015>{{cite book |title=Clinical Anatomy and Physiology for Veterinary Technicians |first1=Thomas P. |last1=Colville |first2=Joanna M. |last2=Bassert |edition=3rd |publisher=Elsevier Health Sciences |year=2015 |isbn=978-0-323-22793-3 |pages=93–95 |url=https://books.google.com/books?id=JRl8BwAAQBAJ&pg=PA93 }}</ref>
Transcription is the process where genetic information in DNA is used to produce a complementary RNA strand. This RNA strand is then processed to give messenger RNA (mRNA), which is free to migrate into the cytoplasm. mRNA molecules bind to protein-RNA complexes called ribosomes located in the cytosol, where they are translated into polypeptide sequences. The ribosome mediates the formation of a polypeptide sequence based on the mRNA sequence. The mRNA sequence directly relates to the polypeptide sequence by binding to transfer RNA (tRNA) adapter molecules in binding pockets within the ribosome.<ref name=Colville_Bassert_2015/> The new polypeptide chain then folds into a functional three-dimensional protein molecule.
=== Motility ===
{{main|Motility}}
Unicellular organisms can move in order to find food or escape predators. Common mechanisms of motion include flagella and cilia,<ref name=Beeby_et_al_2020/> and the projection of pseudopodia in amoeboid movement. Cells in multicellular organisms can move during processes such as wound healing, the immune response, and cancer metastasis. In wound healing in animals, white blood cells move to the wound site to kill the pathogens causing infection. Cell motility involves many receptors, crosslinking, bundling, binding, adhesion, motor and other proteins.<ref name="Ananthakrishnan Ehrlicher 2007">{{cite journal |last1=Ananthakrishnan |first1=R. |last2=Ehrlicher |first2=A. |title=The forces behind cell movement |journal=International Journal of Biological Sciences |volume=3 |issue=5 |pages=303–317 |date=June 2007 |pmid=17589565 |pmc=1893118 |doi=10.7150/ijbs.3.303 |publisher=Biolsci.org }}</ref> The process is divided into three steps: protrusion of the leading edge of the cell, adhesion of the leading edge and de-adhesion at the cell body and rear, and cytoskeletal contraction to pull the cell forward. Each step is driven by physical forces generated by unique segments of the cytoskeleton.<ref name="Alberts2">{{cite book |last1=Alberts |first1=Bruce |title=Molecular biology of the cell |date=2002 |publisher=Garland Science |isbn=0-8153-4072-9 |pages=973–975 |edition=4th}}</ref><ref name="Ananthakrishnan Ehrlicher 2007"/>
==== Navigation, control and communication ====
{{See also|Cybernetics#In biology}}
In August 2020, scientists described one way cells—in particular cells of a slime mold and mouse pancreatic cancer-derived cells—are able to navigate efficiently through a body and identify the best routes through complex mazes: generating gradients after breaking down diffused chemoattractants which enable them to sense upcoming maze junctions before reaching them, including around corners.<ref>{{cite news |last1=Willingham |first1=Emily |title=Cells Solve an English Hedge Maze with the Same Skills They Use to Traverse the Body |url=https://www.scientificamerican.com/article/cells-solve-an-english-hedge-maze-with-the-same-skills-they-use-to-traverse-the-body/ |access-date=7 September 2020 |work=Scientific American |language=en |archive-date=4 September 2020 |archive-url=https://web.archive.org/web/20200904102655/https://www.scientificamerican.com/article/cells-solve-an-english-hedge-maze-with-the-same-skills-they-use-to-traverse-the-body/ |url-status=live }}</ref><ref>{{cite news |title=How cells can find their way through the human body |url=https://phys.org/news/2020-08-cells-human-body.html |access-date=7 September 2020 |work=phys.org |language=en |archive-date=3 September 2020 |archive-url=https://web.archive.org/web/20200903220400/https://phys.org/news/2020-08-cells-human-body.html |url-status=live }}</ref><ref>{{cite journal |last1=Tweedy |first1=Luke |last2=Thomason |first2=Peter A. |last3=Paschke |first3=Peggy I. |last4=Martin |first4=Kirsty |last5=Machesky |first5=Laura M. |last6=Zagnoni |first6=Michele |last7=Insall |first7=Robert H.|title=Seeing around corners: Cells solve mazes and respond at a distance using attractant breakdown |journal=Science |volume=369 |issue=6507 |date=August 2020 |article-number=eaay9792 |pmid=32855311 |doi=10.1126/science.aay9792 |url=https://strathprints.strath.ac.uk/73860/1/Tweedy_etal_Science_2020_Seeing_around_corners_cells_solve_mazes_and_respond.pdf }}</ref>
===Cell death=== {{main|Cell death}}
Cell death occurs when a cell ceases to carry out its functions, as a result of ageing, or types of cell injury (necrosis). Programmed cell death, including apoptosis, and autophagy is a natural process of replacing dead cells with new ones.<ref>{{cite journal |title=Cell death: a review of the major forms of apoptosis, necrosis and autophagy |first=Mark S. |last=D'Arcy |journal=Cell Biology International |date=June 2019 |volume=43 |issue=6 |pages=582–592 |doi=10.1002/cbin.11137 |pmid=30958602 }}</ref><ref>{{cite journal |title=A guide to cell death pathways |last1=Yuan |first1=J. |last2=Ofengeim |first2=D. |journal=Nature Reviews Molecular Cell Biology |volume=25 |pages=379–395 |year=2024 |issue=5 |doi=10.1038/s41580-023-00689-6 |pmid=38110635 }}</ref>
A separate mode of cellular death is known as a mitotic catastrophe, which occurs during mitosis, following the improper progression of, or entrance to the cell cycle. This mechanism operates to prevent genomic instability.<ref name="Galluzzi">{{cite journal |vauthors=Galluzzi L, Vitale I, Aaronson SA |title=Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018 |journal=Cell Death Differ |volume=25 |issue=3 |pages=486–541 |date=March 2018 |pmid=29362479 |pmc=5864239 |doi=10.1038/s41418-017-0012-4 |url=}}</ref><ref name="Vitale">{{cite journal |vauthors=Vitale I, Galluzzi L, Castedo M, Kroemer G |title=Mitotic catastrophe: a mechanism for avoiding genomic instability |journal=Nat Rev Mol Cell Biol |volume=12 |issue=6 |pages=385–92 |date=June 2011 |pmid=21527953 |doi=10.1038/nrm3115 |url=https://zenodo.org/record/3426248}}</ref> Other cell death pathways are described, and include anoikis, pyroptosis, mitoptosis, parthanatos, and necroptosis.<ref name="Hajibabaie2023">{{cite journal |vauthors=Hajibabaie F, Abedpoor N, Mohamadynejad P |title=Types of Cell Death from a Molecular Perspective |journal=Biology |volume=12 |issue=11 |date=November 2023 |page=1426 |pmid=37998025 |pmc=10669395 |doi=10.3390/biology12111426 |doi-access=free |url=}}</ref>
[[File:C elegans stained.jpg|thumb|upright|Staining of a nematode ''Caenorhabditis elegans'' highlights the nuclei of its cells.]]
== Origins == {{main|History of life}}
{{further|Abiogenesis|Evolution of cells}} [[File:Stromatolites.jpg|thumb|Stromatolites are left behind by cyanobacteria, known as blue-green algae. They are among the oldest fossils of life on Earth. This one-billion-year-old fossil is from Glacier National Park in the United States.]]
The origin of cells has to do with the origin of life, which began the history of life on Earth. Small molecules needed for life may have been carried to Earth on meteorites, created at deep-sea hydrothermal vents, or synthesized by lightning in a reducing atmosphere. There is little experimental data defining what the first self-replicating forms were. RNA may have been the earliest self-replicating molecule, as it can both store genetic information and catalyze chemical reactions.<ref name=OrgelLE>{{cite journal |last= Orgel |first=L. E. |title=The origin of life--a review of facts and speculations |journal=Trends in Biochemical Sciences |volume=23 |issue=12 |pages=491–495 |date=December 1998 |pmid=9868373 |doi=10.1016/S0968-0004(98)01300-0 }}</ref> This process required an enzyme to catalyze the RNA reactions, which may have been the early peptides that formed in hydrothermal vents.<ref>{{cite book |chapter=The RNA World: Reality or Dogma? |last=Chatterjee |first=S. |pages=97–107 |year=2023 |title=From Stardust to First Cells |publisher=Springer, Cham |isbn=978-3-031-23397-5 |doi=10.1007/978-3-031-23397-5_10 }}</ref>
Cells emerged around 4 billion years ago.<ref name="NAT-20170301">{{cite journal |last1=Dodd |first1=Matthew S. |last2=Papineau |first2=Dominic |last3=Grenne |first3=Tor |last4=Slack |first4=John F. |last5=Rittner |first5=Martin |last6=Pirajno |first6=Franco |last7=O'Neil |first7=Jonathan |last8=Little |first8=Crispin T.S. |display-authors=3 |title=Evidence for early life in Earth's oldest hydrothermal vent precipitates |journal=Nature |date=1 March 2017 |volume=543 |issue=7643 |pages=60–64 |doi=10.1038/nature21377 |doi-access= |pmid=28252057 |bibcode=2017Natur.543...60D |url=http://eprints.whiterose.ac.uk/112179/ |access-date=2 March 2017 |url-status=live |archive-url=https://web.archive.org/web/20170908201821/http://eprints.whiterose.ac.uk/112179/ |archive-date=8 September 2017}}</ref><ref>{{Cite journal |last1=Betts |first1=Holly C. |last2=Puttick |first2=Mark N. |last3=Clark |first3=James W. |last4=Williams |first4=Tom A. |last5=Donoghue |first5=Philip C. J. |last6=Pisani |first6=Davide |date=20 August 2018 |title=Integrated genomic and fossil evidence illuminates life's early evolution and eukaryote origin |journal=Nature Ecology & Evolution |volume=2 |issue=10 |pages=1556–1562 |doi=10.1038/s41559-018-0644-x |pmid=30127539|pmc=6152910 |bibcode=2018NatEE...2.1556B }}</ref> The first cells were most likely heterotrophs. The early cell membranes were probably simpler and more permeable than later ones, with only a single fatty acid chain per lipid. Lipids spontaneously form bilayered vesicles in water, and could have preceded RNA.<ref name="Griffiths 2007">{{cite journal |last=Griffiths |first=G. |title=Cell evolution and the problem of membrane topology |journal=Nature Reviews. Molecular Cell Biology |volume=8 |issue=12 |pages=1018–1024 |date=December 2007 |pmid=17971839 |doi=10.1038/nrm2287 |s2cid=31072778 |doi-access=free }}</ref><ref name="ScienceDaily 2021">{{cite web |title=First cells may have emerged because building blocks of proteins stabilized membranes |url=https://www.sciencedaily.com/releases/2019/08/190812155502.htm |access-date=2021-09-18 |website=ScienceDaily |archive-date=2021-09-18 |archive-url=https://web.archive.org/web/20210918102211/https://www.sciencedaily.com/releases/2019/08/190812155502.htm |url-status=live }}</ref>
[[File:Symbiogenesis 2 mergers.svg|thumb|upright=1.35|In the theory of symbiogenesis, a merger of an archaean and an aerobic bacterium created the eukaryotes, with aerobic mitochondria, some 2.2 billion years ago. A second merger, 1.6 billion years ago, added chloroplasts, creating the green plants.<ref name=latorre/>]]
Eukaryotic cells were created some 2.2 billion years ago in a process called eukaryogenesis. This is widely agreed to have involved symbiogenesis, in which an archaean and a bacterium came together to create the first eukaryotic common ancestor.<ref name=latorre/> It evolved into a population of single-celled organisms that included the last eukaryotic common ancestor, gaining capabilities along the way.<ref name="Weiss et al 2016"/><ref name="Strassert Irisarri Williams Burki 2021"/>
This cell had a new level of complexity, with a nucleus<ref name="McGrath 2022">{{cite journal |last=McGrath |first=Casey |title=Highlight: Unraveling the Origins of LUCA and LECA on the Tree of Life |journal=Genome Biology and Evolution |volume=14 |issue=6 |date=31 May 2022 |article-number=evac072 |doi=10.1093/gbe/evac072|pmc=9168435 }}</ref><ref name="Weiss et al 2016">{{cite journal |last1=Weiss |first1=Madeline C. |last2=Sousa |first2=F. L. |last3=Mrnjavac |first3=N. |last4=Neukirchen |first4=S. |last5=Roettger |first5=M. |last6=Nelson-Sathi |first6=S. |last7=Martin |first7=William F. |author7-link=William F. Martin |display-authors=3 |s2cid=2997255 |year=2016 |title=The physiology and habitat of the last universal common ancestor |journal=Nature Microbiology |volume=1 |issue=9 |page=16116 |doi=10.1038/nmicrobiol.2016.116 |pmid=27562259 |url=http://complexityexplorer.s3.amazonaws.com/supplemental_materials/3.6+Early+Metabolisms/Weiss_et_al_Nat_Microbiol_2016.pdf }}</ref> and facultatively aerobic mitochondria.<ref name=latorre>{{cite book |last1=Latorre |first1=A. |last2=Durban |first2=A |last3=Moya |first3=A. |last4=Pereto |first4=J. |chapter-url=https://books.google.com/books?id=m3oFebknu1cC&pg=PA326 |chapter=The role of symbiosis in eukaryotic evolution |title=Origins and Evolution of Life: An astrobiological perspective |editor1=Gargaud, Muriel |editor2=López-Garcìa, Purificacion |editor3=Martin, H. |year=2011 |location=Cambridge |publisher=Cambridge University Press |pages=326–339 |isbn=978-0-521-76131-4 |access-date=27 August 2017 |archive-date=24 March 2019 |archive-url=https://web.archive.org/web/20190324055723/https://books.google.com/books?id=m3oFebknu1cC&pg=PA326 |url-status=live }}</ref> It featured at least one centriole and cilium, sex (meiosis and syngamy), peroxisomes, and a dormant cyst with a cell wall of chitin and/or cellulose.<ref>{{cite journal |last=Leander |first=B. S. |title=Predatory protists |journal=Current Biology |volume=30 |issue=10 |pages=R510–R516 |date=May 2020 |pmid=32428491 |doi=10.1016/j.cub.2020.03.052 |bibcode=2020CBio...30.R510L |s2cid=218710816 |doi-access=free }}</ref><ref name="Strassert Irisarri Williams Burki 2021">{{cite journal |last1=Strassert |first1=Jürgen F. H. |last2=Irisarri |first2=Iker |last3=Williams |first3=Tom A. |last4=Burki |first4=Fabien |title=A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids |journal=Nature Communications |volume=12 |issue=1 |date=25 March 2021 |page=1879 |doi=10.1038/s41467-021-22044-z|pmid=33767194 |pmc=7994803 |bibcode=2021NatCo..12.1879S }}</ref> The last eukaryotic common ancestor gave rise to the eukaryotes' crown group, containing the ancestors of animals, fungi, plants, and a diverse range of single-celled organisms.<ref name="Gabaldón">{{cite journal |last=Gabaldón |first=T. |title=Origin and Early Evolution of the Eukaryotic Cell |journal=Annual Review of Microbiology |volume=75 |issue=1 |pages=631–647 |date=October 2021 |pmid=34343017 |doi=10.1146/annurev-micro-090817-062213 |s2cid=236916203 }}</ref><ref name="w1990">{{cite journal |last1=Woese |first1=C.R. |author1-link=Carl Woese |last2=Kandler |first2=Otto |author2-link=Otto Kandler |last3=Wheelis |first3=Mark L. |author3-link=Mark Wheelis |title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=87 |issue=12 |pages=4576–4579 |date=June 1990 |pmid=2112744 |pmc=54159 |doi=10.1073/pnas.87.12.4576 |bibcode=1990PNAS...87.4576W |doi-access=free }}</ref> The green plants were created around 1.6 billion years ago with a second episode of symbiogenesis that added chloroplasts, derived from cyanobacteria.<ref name=latorre/>
===Multicellularity=== Multicellular behavior is demonstrated by microorganisms that are cloned from a single cell and form visible microbial colonies. A microbial consortium of two or more species can form a biofilm by the secretion of extracellular polymeric substances (EPSs).<ref name="Decho">{{cite journal |vauthors=Decho AW, Gutierrez T |title=Microbial Extracellular Polymeric Substances (EPSs) in Ocean Systems |journal=Front Microbiol |volume=8 |issue= |article-number=922 |date=2017 |pmid=28603518 |pmc=5445292 |doi=10.3389/fmicb.2017.00922 |doi-access=free |bibcode=2017FrMic...8..922D |url=}}</ref> Slime molds consist of different groups of microorganisms grouped together in a multicellular-like fashion.
The first evidence of multicellularity in an organism comes from cyanobacteria-like organisms that lived between 3 and 3.5 billion years ago.<ref name="Grosberg2007">{{cite journal |last1= Grosberg |first1=R. K. |last2=Strathmann |first2=R. R. |url=http://www-eve.ucdavis.edu/grosberg/Grosberg%20pdf%20papers/2007%20Grosberg%20%26%20Strathmann.AREES.pdf |title=The evolution of multicellularity: A minor major transition? |journal=Annual Review of Ecology, Evolution, and Systematics |year=2007 |volume=38 |pages=621–654 |doi=10.1146/annurev.ecolsys.36.102403.114735 |access-date=2013-12-23 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304121329/http://www-eve.ucdavis.edu/grosberg/Grosberg%20pdf%20papers/2007%20Grosberg%20%26%20Strathmann.AREES.pdf }}</ref> Cyanobacteria are variable in morphology, filamentous forms exhibit functional cell differentiation such as heterocysts (for nitrogen fixation), akinetes (resting stage cells), and hormogonia (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity.<ref name=Claessen2014>{{cite journal | vauthors = Claessen D, Rozen DE, Kuipers OP, Søgaard-Andersen L, van Wezel GP | title = Bacterial solutions to multicellularity: a tale of biofilms, filaments and fruiting bodies | journal = Nature Reviews. Microbiology | volume = 12 | issue = 2 | pages = 115–124 | date = February 2014 | pmid = 24384602 | doi = 10.1038/nrmicro3178 | hdl-access = free | hdl = 11370/0db66a9c-72ef-4e11-a75d-9d1e5827573d | url = https://pure.rug.nl/ws/files/2328477/2014NatRevMicrobiolClaessen.pdf }}</ref>
[[File:C elegans stained.jpg|thumb|upright|Staining of a nematode ''Caenorhabditis elegans'' highlights the nuclei of its cells.]]
Multicellularity was made possible by the development of the extracellular matrix (ECM) similar in function to the bacterial EPS that consists of extracellular polymeric substances.<ref name="Mazéas2023">{{cite journal |vauthors=Mazéas L, Yonamine R, Barbeyron T, Henrissat B, Drula E, Terrapon N, Nagasato C, Hervé C |title=Assembly and synthesis of the extracellular matrix in brown algae |journal=Semin Cell Dev Biol |volume=134 |issue= |pages=112–124 |date=January 2023 |pmid=35307283 |doi=10.1016/j.semcdb.2022.03.005 |url=https://amu.hal.science/hal-03627114|doi-access=free }}</ref> EPS enables microbial cell adhesion, and is believed to be the first evolutionary step toward multicellular organisms.<ref>{{cite journal |title=The origins of multicellular organisms |first1=Karl J. |last1=Niklas |first2=Stuart A. |last2=Newman |journal=Evolution & Development |volume=15 |issue=1 |date=January 2013 |pages=41–52 |doi=10.1111/ede.12013 |pmid=23331916 |bibcode=2013EvDev..15...41N }}</ref> Basement membranes are a type of specialized extracellular matrix that surrounds most animal tissues, and are essential in their formation.<ref name="Jayadev2017">{{cite journal |last1=Jayadev |first1=Ranjay |last2=Sherwood |first2=David R. |title=Basement membranes |url=https://www.cell.com/current-biology/fulltext/S0960-9822(17)30141-0?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982217301410%3Fshowall%3Dtrue |journal=Current Biology |access-date=16 November 2025 |pages=R207–R211 |language=English |doi=10.1016/j.cub.2017.02.006 |date=20 March 2017 |volume=27 |issue=6 |pmid=28324731 |bibcode=2017CBio...27.R207J }}</ref> Extracellular matrix components of laminin domains, integrated with other proteins such as cadherins have been described in single-celled motile choanoflagellates that pre-dates the evolutionary emergence of basement membranes, one of the two types of ECM.<ref name="Pozzi2017">{{cite journal |vauthors=Pozzi A, Yurchenco PD, Iozzo RV |title=The nature and biology of basement membranes |journal=Matrix Biol |volume=57-58 |issue= |pages=1–11 |date=January 2017 |pmid=28040522 |pmc=5387862 |doi=10.1016/j.matbio.2016.12.009 |url=}}</ref> The emergence of the basement membrane coincided with the origin of multicellularity.<ref name="Jayadev2017"/><ref name="Chang2019">{{cite journal |vauthors=Chang J, Chaudhuri O |title=Beyond proteases: Basement membrane mechanics and cancer invasion |journal=J Cell Biol |volume=218 |issue=8 |pages=2456–2469 |date=August 2019 |pmid=31315943 |doi=10.1083/jcb.201903066 |pmc=6683740 |url=}}</ref> The other type of ECM is the interstial matrix.
The evolution of multicellularity from unicellular ancestors has been replicated in the laboratory, in evolution experiments using predation as the selective pressure.<ref name="Grosberg2007"/>
== History of research == {{main|Cell theory#Discovery of cells}}
[[File:RobertHookeMicrographia1665.jpg|thumb|upright=.6|Robert Hooke's drawing of cells in cork, 1665]]
In 1665, Robert Hooke examined a thin slice of cork under his microscope, and saw a structure of small enclosures. He wrote "I could exceeding plainly perceive it to be all perforated and porous, much like a honeycomb, but that the pores of it were not regular".<ref name="Hooke 1665">{{cite book |last1=Hooke |first1=Robert |author1-link=Robert Hooke |title=Micrographia |date=1665 |chapter=Observation 18 |chapter-url=https://en.wikisource.org/wiki/Micrographia/Chapter_18}}</ref> To further support his theory, Matthias Schleiden and Theodor Schwann studied cells of both animal and plants. What they discovered were significant differences between the two types of cells. This put forth the idea that cells were fundamental to both plants and animals.<ref name="Maton 1997">{{cite book |last=Maton |first=Anthea |url=https://archive.org/details/cellsbuildingblo00mato |title=Cells Building Blocks of Life |publisher=Prentice Hall |year=1997 |isbn=978-0-13-423476-2 |location=New Jersey |pages=44–45 The Cell Theory}}</ref>
* 1632–1723: Antonie van Leeuwenhoek taught himself to make lenses, constructed basic optical microscopes and drew protozoa, such as ''Vorticella'' from rain water, and bacteria from his own mouth.<ref name="Gest 2004">{{cite journal |last=Gest |first=H. |year=2004 |title=The discovery of microorganisms by Robert Hooke and Antoni Van Leeuwenhoek, fellows of the Royal Society |journal=Notes and Records of the Royal Society of London |volume=58 |issue=2 |pages=187–201 |doi=10.1098/rsnr.2004.0055 |pmid=15209075 |bibcode=2004RSN&R..58..187G |s2cid=8297229}}</ref> * 1665: Robert Hooke discovered cells in cork, then in living plant tissue using an early microscope. In his book ''Micrographia'' he coined the term ''cell'' (from Latin ''cellula'', meaning "small room") since they resembled the cells of a monastery.<ref>{{Cite web |title=History of the Cell: Discovering the Cell |url=https://education.nationalgeographic.org/resource/history-cell-discovering-cell |access-date=2025-08-01 |website=education.nationalgeographic.org |language=en}}</ref><ref name="npr12">{{Cite web |date=September 17, 2010 |title=The Origins Of The Word 'Cell' |url=https://www.npr.org/templates/story/story.php?storyId=129934828&t=1628175572746 |url-status=live |archive-url=https://web.archive.org/web/20210805150111/https://www.npr.org/templates/story/story.php?storyId=129934828&t=1628175572746 |archive-date=2021-08-05 |access-date=2021-08-05 |website=National Public Radio }}</ref><ref name="Cellula">{{cite encyclopedia |title=cellŭla |encyclopedia=A Latin Dictionary |year=1879 |publisher=Charlton T. Lewis and Charles Short |url= http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:entry=cellula|access-date=2021-08-05 |isbn=((978-1-9998557-8-9)) |archive-date=2021-08-07 |archive-url= https://web.archive.org/web/20210807122358/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aentry%3Dcellula |url-status= live }}</ref><ref name="Hooke">{{cite book |last=Hooke |first=Robert |author-link=Robert Hooke |title=Micrographia: ...|date=1665 |publisher=Royal Society of London |location=London |page=113 |url=https://archive.org/stream/mobot31753000817897#page/113/mode/2up|quote= ... I could exceedingly plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular [...] these pores, or cells, [...] were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any Writer or Person, that had made any mention of them before this ... |postscript=none}} – Hooke describing his observations on a thin slice of cork. See also: [http://www.ucmp.berkeley.edu/history/hooke.html Robert Hooke] {{Webarchive|url=https://web.archive.org/web/19970606013455/http://www.ucmp.berkeley.edu/history/hooke.html |date=1997-06-06 }}.</ref><ref name="Gest 2004"/> * 1839: Theodor Schwann<ref>{{cite book |last=Schwann |first=Theodor |author-link=Theodor Schwann |year=1839 |title=Mikroskopische Untersuchungen über die Uebereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen |publisher=Sander |place=Berlin |url=http://www.deutschestextarchiv.de/book/show/schwann_mikroskopische_1839}}</ref> and Matthias Jakob Schleiden elucidated the principle that plants and animals are made of cells, concluding that cells are a common unit of structure and development, founding the cell theory.<ref name="biolibre">{{Cite web |date=2018-07-05 |title=4.3: Studying Cells - Cell Theory |url=https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_(Boundless)/04%3A_Cell_Structure/4.03%3A_Studying_Cells_-_Cell_Theory |access-date=2025-08-01 |website=Biology LibreTexts |language=en}}</ref><ref name=Ribatti2018>{{cite journal |last1=Ribatti |first1=Domenico |title=An historical note on the cell theory |journal=Experimental Cell Research |date=March 2018 |volume=364 |issue=1 |pages=1–4 |doi=10.1016/j.yexcr.2018.01.038 |pmid=29391153 }}</ref> * 1855: Rudolf Virchow stated that new cells come from pre-existing cells by cell division (''omnis cellula ex cellula''). * 1931: Ernst Ruska built the first transmission electron microscope at the University of Berlin.<ref name="Ruska">{{cite book |title=The Early Development of Electron Lenses and Electron Microscopy |series=Applied Optics |volume=25 |page=820 |author1=Ernst Ruska |translator=T. Mulvey |isbn=978-3-7776-0364-3 |date=January 1980 |doi=10.1364/AO.25.000820 |bibcode=1986ApOpt..25..820R }}</ref> By 1935, he had built an electron microscope with twice the resolution of a light microscope, revealing previously unresolvable organelles. * 1981: Lynn Margulis published ''Symbiosis in Cell Evolution'' detailing how eukaryotic cells were created by symbiogenesis.<ref name="Cornish-Bowden 2017">{{Cite journal |last=Cornish-Bowden |first=Athel |title=Lynn Margulis and the origin of the eukaryotes |journal=Journal of Theoretical Biology |series=The origin of mitosing cells: 50th anniversary of a classic paper by Lynn Sagan (Margulis) |date=7 December 2017 |volume=434 |page=1 |doi=10.1016/j.jtbi.2017.09.027 |pmid=28992902 |bibcode=2017JThBi.434....1C }}</ref>
== See also ==
{{Div col}} * List of human cell types * ''The Inner Life of the Cell'' * ''Parakaryon myojinensis'' * Syncytium {{div col end}}
== References ==
{{Reflist}}
== External links == {{Commons category|Cells}} * [https://open.oregonstate.education/cellbiology/ Fundamentals of Cell Biology by Lauren Dalton and Robin Young] * {{Cite web|title=The Inner Life of the Cell |url=https://xvivo.com/examples/the-inner-life-of-the-cell/ |website=XVIVO website}} — 2006 animation of molecular mechanisms inside cells
{{Cellular structures}} {{Biological organization}} {{Biotechnology}} {{Authority control}}
{{DEFAULTSORT:Cell (Biology)}} Cell biology Cell anatomy Category:Cellular processes Category:1665 in science