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Prokaryote

Diagram of a typical prokaryotic cell

A prokaryote (/proʊˈkærioʊt, -ət/; less commonly spelled procaryote)[1] is a single-cell organism whose cell lacks a nucleus and other membrane-bound organelles.[2] The word prokaryote comes from the Ancient Greek πρό (pró), meaning 'before', and κάρυον (káruon), meaning 'nut' or 'kernel'.[3][4] In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota.[5] However in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria (formerly Eubacteria) and Archaea (formerly Archaebacteria). Organisms with nuclei are placed in a third domain: Eukaryota.[6]

Prokaryotes evolved before eukaryotes, and lack nuclei, mitochondria, and most of the other distinct organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components were unenclosed within the cytoplasm except for an outer cell membrane, but bacterial microcompartments, which are thought to be quasi-organelles enclosed in protein shells (such as the encapsulin protein cages), have been discovered,[7][8] along with other prokaryotic organelles.[9] While being unicellular, some prokaryotes, such as cyanobacteria, may form colonies held together by biofilms, and large colonies can create multilayered microbial mats. Others, such as myxobacteria, have multicellular stages in their life cycles.[10] Prokaryotes are asexual, reproducing via binary fission without any fusion of gametes, although horizontal gene transfer may take place.

Molecular studies have provided insight into the evolution and interrelationships of the three domains of life.[11] The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization; only eukaryotic cells have an enveloped nucleus that contains its chromosomal DNA, and other characteristic membrane-bound organelles including mitochondria. Distinctive types of prokaryotes include extremophiles and methanogens; these are common in some extreme environments.[2]

  1. ^ "procaryote". Merriam-Webster.com Dictionary. Merriam-Webster. Retrieved 2023-12-30.
  2. ^ a b "Prokaryotes: Single-celled Organisms". North Carolina State University.
  3. ^ Campbell, Neil A. (2003). Biology: Concepts & Connections (4th ed.). San Francisco: Pearson Education. ISBN 978-0805366273.
  4. ^ Harper, Douglas. "prokaryote". Online Etymology Dictionary.
  5. ^ Sapp, Jan (2005). "The Prokaryote-Eukaryote Dichotomy: Meanings and Mythology". Microbiology and Molecular Biology Reviews. 69 (2): 292–305. doi:10.1128/MMBR.69.2.292-305.2005. PMC 1197417. PMID 15944457.
  6. ^ Coté G, De Tullio M (2010). "Beyond Prokaryotes and Eukaryotes: Planctomycetes and Cell Organization". Nature.
  7. ^ Kerfeld CA, Sawaya MR, Tanaka S, Nguyen CV, Phillips M, Beeby M, Yeates TO (August 2005). "Protein structures forming the shell of primitive bacterial organelles". Science. 309 (5736): 936–8. Bibcode:2005Sci...309..936K. CiteSeerX 10.1.1.1026.896. doi:10.1126/science.1113397. PMID 16081736. S2CID 24561197.
  8. ^ Murat D, Byrne M, Komeili A (October 2010). "Cell biology of prokaryotic organelles". Cold Spring Harbor Perspectives in Biology. 2 (10): a000422. doi:10.1101/cshperspect.a000422. PMC 2944366. PMID 20739411.
  9. ^ Murat, Dorothee; Byrne, Meghan; Komeili, Arash (2010-10-01). "Cell Biology of Prokaryotic Organelles". Cold Spring Harbor Perspectives in Biology. 2 (10): a000422. doi:10.1101/cshperspect.a000422. PMC 2944366. PMID 20739411.
  10. ^ Kaiser D (October 2003). "Coupling cell movement to multicellular development in myxobacteria". Nature Reviews. Microbiology. 1 (1): 45–54. doi:10.1038/nrmicro733. PMID 15040179. S2CID 9486133.
  11. ^ Sung KH, Song HK (July 22, 2014). "Insights into the molecular evolution of HslU ATPase through biochemical and mutational analyses". PLOS ONE. 9 (7): e103027. Bibcode:2014PLoSO...9j3027S. doi:10.1371/journal.pone.0103027. PMC 4106860. PMID 25050622.

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