Sun . 19 Nov 2019
TR | RU | UK | KK | BE |


prokaryotes, prokaryotes vs eukaryotes
A prokaryote is a unicellular organism that lacks a membrane-bound nucleus karyon, mitochondria, or any other membrane-bound organelle The word prokaryote comes from the Greek πρό pro "before" and καρυόν karyon "nut or kernel" Prokaryotes can be divided into two domains, Archaea and bacteria In contrast, species with nuclei and organelles are placed in the domain Eukaryota

In the prokaryotes, all the intracellular water-soluble components proteins, DNA and metabolites are located together in the cytoplasm enclosed by the cell membrane, rather than in separate cellular compartments Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells Some prokaryotes, such as cyanobacteria may form large colonies Others, such as myxobacteria, have multicellular stages in their life cycles

Molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus containing chromosomal DNA and organelles The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization Distinctive types of prokaryotes include extremophiles and methanogens; these are common in some extreme environments


  • 1 Structure
  • 2 Morphology
  • 3 Reproduction
  • 4 DNA transfer
  • 5 Sociality
  • 6 Environment
  • 7 Classification
  • 8 Evolution
  • 9 Relationship to eukaryotes
  • 10 See also
  • 11 References
  • 12 External links


Prokaryotes have a prokaryotic cytoskeleton, albeit more primitive than that of the eukaryotes Besides homologues of actin and tubulin MreB and FtsZ, the helically arranged building-block of the flagellum, flagellin, is one of the most significant cytoskeletal proteins of bacteria, as it provides structural backgrounds of chemotaxis, the basic cell physiological response of bacteria At least some prokaryotes also contain intracellular structures that can be seen as primitive organelles Membranous organelles or intracellular membranes are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, such as photosynthesis or chemolithotrophy In addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles eg carboxysomes or gas vacuoles

Most prokaryotes are between 1 µm and 10 µm, but they can vary in size from 02 µm Mycoplasma genitalium to 750 µm Thiomargarita namibiensis

Prokaryotic cell structure
Flagellum only in some types of prokaryotes

Long, whip-like protrusion that aids cellular locomotion

Cell membrane

Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell

Cell wall except genera Mycoplasma and Thermoplasma

Outer covering of most cells that protects the bacterial cell and gives it shape


A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules


Cell structures responsible for protein production


Area of the cytoplasm that contains the single bacterial DNA molecule

Glycocalyx only in some types of prokaryotes

A glycoprotein-polysaccharide covering that surrounds the cell membranes



Prokaryotic cells have various shapes; the four basic shapes of bacteria are:

  • Cocci – spherical
  • Bacilli – rod-shaped
  • Spirochaete – spiral-shaped
  • Vibrio – comma-shaped

The archaeon Haloquadratum has flat square-shaped cells


Bacteria and archaea reproduce through asexual reproduction, usually by binary fission Genetic exchange and recombination still occur, but this is a form of horizontal gene transfer and is not a replicative process, simply involving the transference of DNA between two cells, as in bacterial conjugation

DNA transfer

DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has been mainly studied in bacteria In bacteria, gene transfer occurs by three processes These are 1 bacterial virus bacteriophage-mediated transduction, 2 plasmid-mediated conjugation, and 3 natural transformation Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, rather than an adaptation of the host bacteria The transfer of bacterial DNA is under the control of the bacteriophage’s genes rather than bacterial genes Conjugation in the well-studied E coli system is controlled by plasmid genes, and is an adaptation for distributing copies of a plasmid from one bacterial host to another Infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium Plasmid mediated transfer of host bacterial DNA conjugation also appears to be an accidental process rather than a bacterial adaptation

Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium Unlike transduction and conjugation, transformation is clearly a bacterial adaptation for DNA transfer, because it depends on numerous bacterial gene products that specifically interact to perform this complex process For a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called competence About 40 genes are required in Bacillus subtilis for the development of competence The length of DNA transferred during B subtilis transformation can be as much as a third to the whole chromosome Transformation is a common mode of DNA transfer, and 67 prokaryotic species are thus far known to be naturally competent for transformation

Among archaea, Halobacterium volcanii forms cytoplasmic bridges between cells that appear to be used for transfer of DNA from one cell to another Another archaeon, Sulfolobus solfataricus, transfers DNA between cells by direct contact Frols et al found that exposure of S solfataricus to DNA damaging agents induces cellular aggregation, and suggested that cellular aggregation may enhance DNA transfer among cells to provide increased repair of damaged DNA via homologous recombination


While prokaryotes are considered strictly unicellular, most can form stable aggregate communities When such communities are encased in a stabilizing polymer matrix "slime", they may be called "biofilms" Cells in biofilms often show distinct patterns of gene expression phenotypic differentiation in time and space Also, as with multicellular eukaryotes, these changes in expression often appear to result from cell-to-cell signaling, a phenomenon known as quorum sensing

Biofilms may be highly heterogeneous and structurally complex and may attach to solid surfaces, or exist at liquid-air interfaces, or potentially even liquid-liquid interfaces Bacterial biofilms are often made up of microcolonies approximately dome-shaped masses of bacteria and matrix separated by "voids" through which the medium eg, water may flow easily The microcolonies may join together above the substratum to form a continuous layer, closing the network of channels separating microcolonies This structural complexity—combined with observations that oxygen limitation a ubiquitous challenge for anything growing in size beyond the scale of diffusion is at least partially eased by movement of medium throughout the biofilm—has led some to speculate that this may constitute a circulatory system and many researchers have started calling prokaryotic communities multicellular for example Differential cell expression, collective behavior, signaling, programmed cell death, and in some cases discrete biological dispersal events all seem to point in this direction However, these colonies are seldom if ever founded by a single founder in the way that animals and plants are founded by single cells, which presents a number of theoretical issues Most explanations of co-operation and the evolution of multicellularity have focused on high relatedness between members of a group or colony, or whole organism If a copy of a gene is present in all members of a group, behaviors that promote cooperation between members may permit those members to have on average greater fitness than a similar group of selfish individuals see inclusive fitness and Hamilton's rule

Should these instances of prokaryotic sociality prove to be the rule rather than the exception, it would have serious implications for the way we view prokaryotes in general, and the way we deal with them in medicine Bacterial biofilms may be 100 times more resistant to antibiotics than free-living unicells and may be nearly impossible to remove from surfaces once they have colonized them Other aspects of bacterial cooperation—such as bacterial conjugation and quorum-sensing-mediated pathogenicity, present additional challenges to researchers and medical professionals seeking to treat the associated diseases


Prokaryotes have diversified greatly throughout their long existence The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, studied in cryobiology or as hot as undersea hydrothermal vents and land-based hot springs

Prokaryotes live in nearly all environments on Earth Some archaea and bacteria thrive in harsh conditions, such as high temperatures thermophiles or high salinity halophiles Organisms such as these are referred to as extremophiles Many archaea grow as plankton in the oceans Symbiotic prokaryotes live in or on the bodies of other organisms, including humans


Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes

In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea originally Eubacteria and Archaebacteria because of the major differences in the structure and genetics between the two groups of organisms Archaea were originally thought to be extremophiles, living only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats The resulting arrangement of Eukaryota also called "Eukarya", Bacteria, and Archaea is called the three-domain system, replacing the traditional two-empire system

One criticism of the dichotomous prokaryote-eukaryote distinction points out that the word "prokaryote" is based on what these organisms are not they are not eukaryotic, rather than what they are either archaea or bacteria


Main article: Molecular evolution Phylogenetic ring showing the diversity of prokaryotes, and symbiogenetic origins of eukaryotes

The current model of the evolution of the first living organisms is that these were some form of prokaryotes, which may have evolved out of protocells In general, the eukaryotes are thought to have evolved later in the history of life

However, some authors have questioned this conclusion, arguing that the current set of prokaryotic species may have evolved from more complex eukaryotic ancestors through a process of simplification

Others have argued that the three domains of life arose simultaneously, from a set of varied cells that formed a single gene pool

This controversy was summarized in 2005:

There is no consensus among biologists concerning the position of the eukaryotes in the overall scheme of cell evolution Current opinions on the origin and position of eukaryotes span a broad spectrum including the views that eukaryotes arose first in evolution and that prokaryotes descend from them, that eukaryotes arose contemporaneously with eubacteria and archeabacteria and hence represent a primary line of descent of equal age and rank as the prokaryotes, that eukaryotes arose through a symbiotic event entailing an endosymbiotic origin of the nucleus, that eukaryotes arose without endosymbiosis, and that eukaryotes arose through a symbiotic event entailing a simultaneous endosymbiotic origin of the flagellum and the nucleus, in addition to many other models, which have been reviewed and summarized elsewhere

The oldest known fossilized prokaryotes were laid down approximately 35 billion years ago, only about 1 billion years after the formation of the Earth's crust Eukaryotes only appear in the fossil record later, and may have formed from endosymbiosis of multiple prokaryote ancestors The oldest known fossil eukaryotes are about 17 billion years old However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago

While Earth is the only place in the universe where life is known to exist, some have suggested that there is evidence on Mars of fossil or living prokaryotes However, this possibility remains the subject of considerable debate and skepticism

Relationship to eukaryotes

The division between prokaryotes and eukaryotes is usually considered the most important distinction or difference among organisms The distinction is that eukaryotic cells have a "true" nucleus containing their DNA, whereas prokaryotic cells do not have a nucleus Both eukaryotes and prokaryotes contain large RNA/protein structures called ribosomes, which produce protein

Another difference is that ribosomes in prokaryotes are smaller than in eukaryotes However, two organelles found in many eukaryotic cells, mitochondria and chloroplasts, contain ribosomes similar in size and makeup to those found in prokaryotes This is one of many pieces of evidence that mitochondria and chloroplasts are themselves descended from free-living bacteria This theory holds that early eukaryotic cells took in primitive prokaryotic cells by phagocytosis and adapted themselves to incorporate their structures, leading to the mitochondria we see today

The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids

Prokaryotes lack mitochondria and chloroplasts Instead, processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic cell membrane However, prokaryotes do possess some internal structures, such as prokaryotic cytoskeletons It has been suggested that the bacterial order Planctomycetes have a membrane around their nucleoid and contain other membrane-bound cellular structures However, further investigation revealed that Planctomycetes cells are not compartmentalized or nucleated and like the other bacterial membrane systems are all interconnected

Prokaryotic cells are usually much smaller than eukaryotic cells Therefore, prokaryotes have a larger surface-area-to-volume ratio, giving them a higher metabolic rate, a higher growth rate, and as a consequence, a shorter generation time than eukaryotes

See also

  • Molecular and cell biology portal
  • Biology portal
  • Eukaryote
  • Bacterial cell structure
  • Evolution of sexual reproduction
  • List of sequenced archaeal genomes
  • List of sequenced bacterial genomes
  • Monera, an obsolete kingdom including Archaea and Bacteria
  • Nanobacterium
  • Nanobe
  • Parakaryon
  • Prion
  • Symbiogenesis
  • Three-domain system
  • Virus


  1. ^ a b NC State University "Prokaryotes: Single-celled Organisms" 
  2. ^ a b c d Campbell, N "Biology:Concepts & Connections" Pearson Education San Francisco: 2003
  3. ^ "prokaryote" Online Etymology Dictionary 
  4. ^ Gary Coté & Mario De Tullio 2010 "Beyond Prokaryotes and Eukaryotes: Planctomycetes and Cell Organization" Nature  CS1 maint: Uses authors parameter link
  5. ^ Kerfeld, C A; Sawaya, M R; Tanaka, S; Nguyen, C V; et al 5 August 2005 "Protein structures forming the shell of primitive bacterial organelles" Science 309 5736: 936–8 Bibcode:2005Sci309936K doi:101126/science1113397 PMID 16081736 
  6. ^ Dorothee Murat; Meghan Byrne & Arash Komeili October 2010 "Cell Biology of Prokaryotic Organelles" Cold Spring Harb Perspect Biol 2: a000422 doi:101101/cshperspecta000422 PMC 2944366 PMID 20739411 
  7. ^ Kaiser D October 2003 "Coupling cell movement to multicellular development in myxobacteria" Nat Rev Microbiol 1 1: 45–54 doi:101038/nrmicro733 PMID 15040179 
  8. ^ Kwang Hoon Sung & Hyun Kyu Song July 22, 2014 "Insights into the Molecular Evolution of HslU ATPase through Biochemical and Mutational Analyses" PLOS 9: e103027 doi:101371/journalpone0103027  CS1 maint: Uses authors parameter link
  9. ^ Bauman, Robert W; Tizard, Ian R; Machunis-Masouka, Elizabeth 2006 Microbiology San Francisco: Pearson Benjamin Cummings ISBN 0-8053-7693-3 
  10. ^ Stoeckenius W 1 October 1981 "Walsby's square bacterium: fine structure of an orthogonal procaryote" J Bacteriol 148 1: 352–60 PMC 216199 PMID 7287626 
  11. ^ Chen I; Dubnau D March 2004 "DNA uptake during bacterial transformation" Nat Rev Microbiol 2 3: 241–9 doi:101038/nrmicro844 PMID 15083159 
  12. ^ Solomon JM; Grossman AD April 1996 "Who's competent and when: regulation of natural genetic competence in bacteria" Trends Genet 12 4: 150–5 doi:101016/0168-95259610014-7 PMID 8901420 
  13. ^ Akamatsu T; Taguchi H April 2001 "Incorporation of the whole chromosomal DNA in protoplast lysates into competent cells of Bacillus subtilis" Biosci Biotechnol Biochem 65 4: 823–9 doi:101271/bbb65823 PMID 11388459 
  14. ^ Saito Y; Taguchi H; Akamatsu T March 2006 "Fate of transforming bacterial genome following incorporation into competent cells of Bacillus subtilis: a continuous length of incorporated DNA" J Biosci Bioeng 101 3: 257–62 doi:101263/jbb101257 PMID 16716928 
  15. ^ Johnsborg O; Eldholm V; Håvarstein LS December 2007 "Natural genetic transformation: prevalence, mechanisms and function" Res Microbiol 158 10: 767–78 doi:101016/jresmic200709004 PMID 17997281 
  16. ^ Rosenshine I; Tchelet R; Mevarech M September 1989 "The mechanism of DNA transfer in the mating system of an archaebacterium" Science 245 4924: 1387–9 Bibcode:1989Sci2451387R doi:101126/science2818746 PMID 2818746 
  17. ^ Fröls S; Ajon M; Wagner M; et al November 2008 "UV-inducible cellular aggregation of the hyperthermophilic archaeon Sulfolobus solfataricus is mediated by pili formation" Mol Microbiol 70 4: 938–52 doi:101111/j1365-2958200806459x PMID 18990182 
  18. ^ Madigan, Michael T 2012 Brock biology of microorganisms 13th ed San Francisco: Benjamin Cummings ISBN 9780321649638 
  19. ^ "Direct Observations" The Biofilm Primer Springer Series on Biofilms 1 2007 pp 3–4 doi:101007/978-3-540-68022-2_2 ISBN 978-3-540-68021-5 
  20. ^ Costerton JW; Lewandowski Z; Caldwell DE; Korber DR; et al 1995 "Microbial biofilms" Annu Rev Microbiol 49: 711–45 doi:101146/annurevmi49100195003431 PMID 8561477 
  21. ^ Shapiro JA 1998 "Thinking about bacterial populations as multicellular organisms" PDF Annu Rev Microbiol 52: 81–104 doi:101146/annurevmicro52181 PMID 9891794 
  22. ^ Chua SL, Liu Y, Yam JK, Tolker-Nielsen T, Kjelleberg S, Givskov M, Yang L 2014 "Dispersed cells represent a distinct stage in the transition from bacterial biofilm to planktonic lifestyles" Nature Communications 5 doi:101038/ncomms5462 
  23. ^ Hamilton WD July 1964 "The genetical evolution of social behaviour II" J Theor Biol 7 1: 17–52 doi:101016/0022-51936490039-6 PMID 5875340 
  24. ^ Balaban, N; Ren, D; Givskov, M; Rasmussen, T B 2008 "Introduction" Control of Biofilm Infections by Signal Manipulation Springer Series on Biofilms 2 p 1 doi:101007/7142_2007_006 ISBN 978-3-540-73852-7 
  25. ^ Costerton JW; Stewart PS; Greenberg EP May 1999 "Bacterial biofilms: a common cause of persistent infections" Science 284 5418: 1318–22 Bibcode:1999Sci2841318C doi:101126/science28454181318 PMID 10334980 
  26. ^ CMichael Hogan 2010 Extremophile, Encyclopedia of Earth, National Council of Science & the Environment, eds E,Monosson & CCleveland
  27. ^ Woese CR March 1994 "There must be a prokaryote somewhere: microbiology's search for itself" Microbiol Rev 58 1: 1–9 PMC 372949 PMID 8177167 
  28. ^ Sapp J June 2005 "The prokaryote-eukaryote dichotomy: meanings and mythology" Microbiol Mol Biol Rev 69 2: 292–305 doi:101128/MMBR692292-3052005 PMC 1197417 PMID 15944457 
  29. ^ Zimmer C August 2009 "Origins On the origin of eukaryotes" Science 325 5941: 666–8 doi:101126/science325_666 PMID 19661396 
  30. ^ Brown, JR February 2003 "Ancient Horizontal Gene Transfer" Nature Reviews Genetics 4 2: 121–132 doi:101038/nrg1000 PMID 12560809 
  31. ^ Forterre P; Philippe H October 1999 "Where is the root of the universal tree of life" BioEssays 21 10: 871–9 doi:101002/SICI1521-187819991021:10<871::AID-BIES10>30CO;2-Q PMID 10497338 
  32. ^ Poole, Anthony; Jeffares, Daniel; Penny, David September 1999 "Early evolution: prokaryotes, the new kids on the block" BioEssays 21 10: 880–9 doi:101002/SICI1521-187819991021:10<880::AID-BIES11>30CO;2-P PMID 10497339 
  33. ^ Woese C June 1998 "The universal ancestor" Proc Natl Acad Sci USA 95 12: 6854–9 Bibcode:1998PNAS956854W doi:101073/pnas95126854 PMC 22660 PMID 9618502 
  34. ^ Martin, William Woe is the Tree of Life In Microbial Phylogeny and Evolution: Concepts and Controversies ed Jan Sapp Oxford: Oxford University Press; 2005: 139
  35. ^ Carl Woese, J Peter Gogarten, "When did eukaryotic cells cells with nuclei and other internal organelles first evolve What do we know about how they evolved from earlier life-forms" Scientific American, October 21, 1999
  36. ^ McSween HY 1997 "Evidence for life in a martian meteorite" GSA Today 7 7: 1–7 PMID 11541665 
  37. ^ McKay DS; Gibson EK; Thomas-Keprta KL; et al August 1996 "Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001" Science 273 5277: 924–30 Bibcode:1996Sci273924M doi:101126/science2735277924 PMID 8688069 
  38. ^ Crenson, Matt 2006-08-06 "After 10 years, few believe life on Mars" Associated Press on spacecom] Retrieved 2006-08-06 
  39. ^ Scott ER 1999 "Origin of carbonate-magnetite-sulfide assemblages in Martian meteorite ALH84001" J Geophys Res 104 E2: 3803–13 Bibcode:1999JGR1043803S doi:101029/1998JE900034 PMID 11542931 
  40. ^ The Molecular Biology of the Cell, fourth edition Bruce Alberts, et al Garland Science 2002 pg 808 ISBN 0-8153-3218-1
  41. ^ Thanbichler M; Wang S; Shapiro L 2005 "The bacterial nucleoid: a highly organized and dynamic structure" J Cell Biochem 96 3: 506–21 doi:101002/jcb20519 PMID 15988757 
  42. ^ Harold F 1 June 1972 "Conservation and transformation of energy by bacterial membranes" Bacteriol Rev 36 2: 172–230 PMC 408323 PMID 4261111 
  43. ^ Shih YL; Rothfield L 2006 "The bacterial cytoskeleton" Microbiol Mol Biol Rev 70 3: 729–54 doi:101128/MMBR00017-06 PMC 1594594 PMID 16959967 
  44. ^ Michie KA; Löwe J 2006 "Dynamic filaments of the bacterial cytoskeleton" PDF Annu Rev Biochem 75: 467–92 doi:101146/annurevbiochem75103004142452 PMID 16756499 Archived from the original PDF on November 17, 2006 
  45. ^ Fuerst J 2005 "Intracellular compartmentation in planctomycetes" Annu Rev Microbiol 59: 299–328 doi:101146/annurevmicro59030804121258 PMID 15910279 
  46. ^ Santarella-Mellwig, R; Pruggnaller, S; Roos, N; Mattaj, I; et al 2013 "Three-Dimensional Reconstruction of Bacteria with a Complex Endomembrane System" PLoS Biology 11: e1001565 doi:101371/journalpbio1001565 PMC 3660258 PMID 23700385 

External links

  • Prokaryote versus eukaryote, BioMineWiki
  • The Taxonomic Outline of Bacteria and Archaea
  • The Prokaryote-Eukaryote Dichotomy: Meanings and Mythology
  • Quiz on prokaryote anatomy
  • TOLWEB page on Eukaryote-Prokaryote phylogeny

 This article incorporates public domain material from the NCBI document "Science Primer"

prokaryote coloring, prokaryote definition biology, prokaryote diagram, prokaryote examples, prokaryote structure, prokaryote vs eukaryote, prokaryotes, prokaryotes vs eukaryotes, prokaryotes vs eukaryotes venn diagram, prokaryotic cell

Prokaryote Information about


  • user icon

    Prokaryote beatiful post thanks!


Prokaryote viewing the topic.
Prokaryote what, Prokaryote who, Prokaryote explanation

There are excerpts from wikipedia on this article and video

Random Posts

IP address blocking

IP address blocking

IP address blocking prevents connection between a server or website and certain IP addresses or rang...
Gisele Bündchen

Gisele Bündchen

Gisele Caroline Bündchen1 Portuguese pronunciation: ʒiˈzɛli kaɾoˈlini ˈbĩtʃẽj, German pronuncia...
Sheldon, West Midlands

Sheldon, West Midlands

Sheldon is an area of east Birmingham, England Historically part of Warwickshire, it is close to the...
Beverly, Chicago

Beverly, Chicago

Beverly is one of the 77 community areas of Chicago, Illinois It is located on the South Side on the...