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A typical animal cell. Within the cytoplasm, the major organelles and cellular structures include: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (6) Golgi apparatus (7) cytoskeleton (8) smooth endoplasmic reticulum (9) mitochondria (10) vacuole (11) cytosol (12) lysosome (13) centriole.

In cell biology, an organelle (pronounced /ÉrÉ¡ÉˈnÉl/) is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer.

The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells. Prokaryotes were once thought not to have organelles, but some examples have now been identified.[1]


[edit] History and terminology

In biology, organs are defined as confined functional units within an organism.[2] The analogy of bodily organs to microscopic cellular substructures is obvious, as from even early works, authors of respective textbooks rarely elaborate on the distinction between the two.

Credited as the first[3][4][5] to use a diminutive of organ (i.e. little organ) for cellular structures was German zoologist Karl August Möbius (1884), who used the term "organula" [6] (plural form of organulum, the diminutive of latin organum). From the context, it is clear that he referred to reproduction related structures of protists. In a footnote, which was published as a correction in the next issue of the journal, he justified his suggestion to call organs of unicellular organisms "organella" since they are only differently formed parts of one cell, in contrast to multicellular organs of multicellular organisms. Thus, the original definition was limited to structures of unicellular organisms.

It would take several years before organulum, or the later term organelle, became accepted and expanded in meaning to include subcellular structures in multicellular organisms. Books around 1900 from Valentin Häcker,[7] Edmund Wilson[8] and Oscar Hertwig[9] still referred to cellular organs. Later, both terms came to be used side by side: Bengt Lidforss wrote 1915 (in German) about "Organs or Organells".[10]

Around 1920, the term organelle was used to describe propulsion structures ("motor organelle complex", i.e., flagella and their anchoring)[11] and other protist structures, such as ciliates.[12] Alfred Kühn wrote about centrioles as division organelles, although he stated that, for Vahlkampfias, the alternative 'organelle' or 'product of structural build-up' had not yet been decided, without explaining the difference between the alternatives.[13]

In his 1953 textbook, Max Hartmann used the term for extracellular (pellicula, shells, cell walls) and intracellular skeletons of protists.[14]

Later, the now-widely-used[15][16][17][18] definition of organelle emerged, after which only cellular structures with surrounding membrane had been considered organelles. However, the more original definition of subcellular functional unit in general still coexists.[19][20]

In 1978, Albert Frey-Wyssling suggested that the term organelle should refer only to structures that convert energy, such as centrosomes, ribosomes, and nucleoli.[21][22] This new definition, however, did not win wide recognition.

[edit] Examples

While most cell biologists consider the term organelle to be synonymous with "cell compartment", other cell biologists choose to limit the term organelle to include only those that are DNA-containing, having originated from formerly-autonomous microscopic organisms acquired via endosymbiosis.[23][24][25]

The most notable of these organelles having originated from endosymbiont bacteria are:

Other organelles are also suggested to have endosymbiotic origins, (notably the flagellum - see evolution of flagella).

Under the more restricted definition of membrane-bound structures, some parts of the cell do not qualify as organelles. Nevertheless, the use of organelle to refer to non-membrane bound structures such as ribosomes is quite common[26]. This has led some texts to delineate between membrane-bound and non-membrane bound organelles[27]. These structures are large assemblies of macromolecules that carry out particular and specialized functions, but they lack membrane boundaries. Such cell structures include:

[edit] Eukaryotic organelles

Eukaryotes are one of the most structurally complex cell type, and by definition are in part organized by smaller interior compartments, that are themselves enclosed by lipid membranes that resemble the outermost cell membrane. The larger organelles, such as the nucleus and vacuoles, are easily visible with the light microscope. They were among the first biological discoveries made after the invention of the microscope.

Not all eukaryotic cells have every one of the organelles listed below. Exceptional organisms have cells which do not include some organelles that might otherwise be considered universal to eukaryotes (such as mitochondria).[28] There are also occasional exceptions to the number of membranes surrounding organelles, listed in the tables below (e.g., some that are listed as double-membrane are sometimes found with single or triple membranes). In addition, the number of individual organelles of each type found in a given cell varies depending upon the function of that cell.

Major eukaryotic organelles
Organelle Main function Structure Organisms Notes
chloroplast (plastid) photosynthesis double-membrane compartment plants, protists (rare kleptoplastic organisms) has some genes; theorized to be engulfed by the ancestral eukaryotic cell (endosymbiosis)
endoplasmic reticulum translation and folding of new proteins (rough endoplasmic reticulum), expression of lipids (smooth endoplasmic reticulum) single-membrane compartment all eukaryotes rough endoplasmic reticulum is covered with ribosomes, has folds that are flat sacs; smooth endoplasmic reticulum has folds that are tubular
Golgi apparatus sorting and modification of proteins single-membrane compartment all eukaryotes cis-face (convex) nearest to rough endoplasmic reticulum; trans-face (concave) farthest from rough endoplasmic reticulum
mitochondrion energy production double-membrane compartment most eukaryotes has some DNA; theorized to be engulfed by the ancestral eukaryotic cell (endosymbiosis)
vacuole storage, homeostasis single-membrane compartment eukaryotes
nucleus DNA maintenance, RNA transcription double-membrane compartment all eukaryotes has bulk of genome

Mitochondria and chloroplasts, which have double-membranes and their own DNA, are believed to have originated from incompletely consumed or invading prokaryotic organisms, which were adopted as a part of the invaded cell. This idea is supported in the Endosymbiotic theory.

Minor eukaryotic organelles and cell components
Organelle/Macromolecule Main function Structure Organisms
acrosome helps spermatoza fuse with ovum single-membrane compartment many animals
autophagosome vesicle which sequesters cytoplasmic material and organelles for degradation double-membrane compartment all eukaryotic cells
centriole anchor for cytoskeleton Microtubule protein animals
cilium movement in or of external medium; "critical developmental signaling pathway"[29]. Microtubule protein animals, protists, few plants
eyespot apparatus detects light, allowing phototaxis to take place green algae and other unicellular photosynthetic organisms such as euglenids
glycosome carries out glycolysis single-membrane compartment Some protozoa, such as Trypanosomes.
glyoxysome conversion of fat into sugars single-membrane compartment plants
hydrogenosome energy & hydrogen production double-membrane compartment a few unicellular eukaryotes
lysosome breakdown of large molecules (e.g., proteins + polysaccharides) single-membrane compartment most eukaryotes
melanosome pigment storage single-membrane compartment animals
mitosome not characterized double-membrane compartment a few unicellular eukaryotes
myofibril muscular contraction bundled filaments animals
nucleolus ribosome production protein-DNA-RNA most eukaryotes
parenthesome not characterized not characterized fungi
peroxisome breakdown of metabolic hydrogen peroxide single-membrane compartment all eukaryotes
ribosome translation of RNA into proteins RNA-protein eukaryotes, prokaryotes
vesicle material transport single-membrane compartment all eukaryotes

Other related structures:

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.[30]

[edit] Prokaryotic organelles

Prokaryotes are not as structurally complex as eukaryotes, and were once thought not to have any internal structures enclosed by lipid membranes. In the past, they were often viewed as having little internal organization; but, slowly, details are emerging about prokaryotic internal structures. An early false turn was the idea developed in the 1970s that bacteria might contain membrane folds termed mesosomes, but these were later shown to be artifacts produced by the chemicals used to prepare the cells for electron microscopy.[31]

However, more recent research has revealed that at least some prokaryotes have microcompartments such as carboxysomes. These subcellular compartments are 100 - 200 nm in diameter and are enclosed by a shell of proteins.[1] Even more striking is the description of membrane-bound magnetosomes in bacteria,[32][33] as well as the nucleus-like structures of the Planctomycetes that are surrounded by lipid membranes.[34]

Prokaryotic organelles and cell components
Organelle/Macromolecule Main function Structure Organisms
carboxysome carbon fixation protein-shell compartment some bacteria
chlorosome photosynthesis light harvesting complex green sulfur bacteria
flagellum movement in external medium protein filament some prokaryotes and eukaryotes
magnetosome magnetic orientation inorganic crystal, lipid membrane magnetotactic bacteria
nucleoid DNA maintenance, transcription to RNA DNA-protein prokaryotes
plasmid DNA exchange circular DNA some bacteria
ribosome translation of RNA into proteins RNA-protein eukaryotes, prokaryotes
thylakoid photosynthesis photosystem proteins and pigments mostly cyanobacteria

[edit] Proteins and organelles

The function of a protein is closely correlated with which organelle it resides. Some methods for predicting which organelle an uncharacterized protein is located according to its amino acid composition were proposed [35] [36]. And some methods were based pseudo amino acid composition [37] [38] [39] [40].

[edit] See also

[edit] References

  1. ^ a b 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 (New York, N.Y.) 309 (5736): 936â8. doi:10.1126/science.1113397. PMID 16081736. 
  2. ^ Lynsey Peterson (2010-04-19). "Mastering the Parts of a Cell" (HTML). Lesson Planet. http://www.lessonplanet.com/directory_articles/biology_lesson_plans/19_April_2010/363/mastering_the_parts_of_a_cell. Retrieved 2010-04-19. 
  3. ^ Bütschli, O. (1888). Dr. H. G. Bronn's Klassen u. Ordnungen des Thier-Reichs wissenschaftlich dargestellt in Wort und Bild. Erster Band. Protozoa. Dritte Abtheilung: Infusoria und System der Radiolaria.. pp. 1412. "Die Vacuolen sind demnach in strengem Sinne keine beständigen Organe oder O r g a n u l a (wie Möbius die Organe der Einzelligen im Gegensatz zu denen der Vielzelligen zu nennen vorschlug)." 
  4. ^ Amer. Naturalist. 23, 1889, S. 183: âžIt may possibly be of advantage to use the word organula here instead of organ, following a suggestion by Möbius. Functionally-differentiated multicellular aggregates in multicellular forms or metazoa are in this sense organs, while, for functionally-differentiated portions of unicellular organisms or for such differentiated portions of the unicellular germ-elements of metazoa, the diminutive organula is appropriate.â Cited after : Oxford English Dictionary online, entry for âžorganelleâ.
  5. ^ 'Journal de l'anatomie et de la physiologie normales et pathologiques de l'homme et des animaux' at Google Books
  6. ^ Möbius, K. (September 1884). "Das Sterben der einzelligen und der vielzelligen Tiere. Vergleichend betrachtet". Biologisches Centralblatt 4 (13,14): 389â392, 448. http://www.dietzellab.de/goodies/history/. "Während die Fortpflanzungszellen der vielzelligen Tiere unthätig fortleben bis sie sich loslösen, wandern und entwickeln, treten die einzelligen Tiere auch durch die an der Fortpflanzung beteiligten Leibesmasse in Verkehr mit der Außenwelt und viele bilden sich dafür auch besondere Organula". Footnote on p. 448: "Die Organe der Heteroplastiden bestehen aus vereinigten Zellen. Da die Organe der Monoplastiden nur verschieden ausgebildete Teile e i n e r Zelle sind schlage ich vor, sie âžOrganulaâ zu nennen". 
  7. ^ Häcker, Valentin (1899). Zellen- und Befruchtungslehre. Jena: Verlag von Gustav Fisher. 
  8. ^ Wilson, Edmund B. (1900). The cell in Development and Inheritance (second ed.). New York: The Macmillan Company. 
  9. ^ Hertwig, Oscar (1906). Allgemeine Biologie. Zweite Auflage des Lehrbuchs âžDie Zelle und die Gewebeâ. Jena: Verlag von Gustav Fischer. 
  10. ^ Lidforss, B. (1915). "Protoplasma". in Paul Hinneberg. Allgemeine Biologie. Leipzig, Berlin: Verlag von B.G.Teubner. pp. 227 (218â264). "Eine Neubildung dieser Organe oder Organellen findet wenigstens bei höheren Pflanzen nicht statt" 
  11. ^ Kofoid CA, Swezy O (1919). "Flagellate Affinities of Trichonympha". Proc. Natl. Acad. Sci. U.S.A. 5 (1): 9â16. doi:10.1073/pnas.5.1.9. PMID 16576345. 
  12. ^ Cl. Hamburger, Handwörterbuch der Naturw. Bd. V, .S. 435. Infusorien. cited after Petersen, Hans (May 1919). "Über den Begriff des Lebens und die Stufen der biologischen Begriffsbildung". Archiv für Entwicklungsmechanik der Organismen (now: Development Genes and Evolution) 45 (3): 423â442. doi:10.1007/BF02554406. ISSN 1432-041X. 
  13. ^ Kühn, Alfred (1920). "Untersuchungen zur kausalen Analyse der Zellteilung. I. Teil: Zur Morphologie und Physiologie der Kernteilung von Vahlkampfia bistadialis". Archiv für Entwicklungsmechanik der Organismen (now: Development Genes and Evolution) 46: 259â327. doi:10.1007/BF02554424. "die Alternative: Organell oder Produkt der Strukturbildung". 
  14. ^ Hartmann, Max (1953). Allgemeine Biologie (4. Aufl. ed.). Stuttgart: Gustav Fisher Verlag. 
  15. ^ Nultsch, Allgemeine Botanik, 11. Aufl. 2001, Thieme Verlag
  16. ^ Wehner/Gehring, Zoologies, 23. Aufl. 1995, Thieme Verlag
  17. ^ Alberts et al., Molecular Biology of the Cell, 4. ed. 2002, online via "NCBI-Bookshelf"
  18. ^ Brock, Mikrobiologie, 2. korrigierter Nachdruck (2003), der 1. Aufl. von 2001
  19. ^ Strasburgers Lehrbuch der Botanik für Hochschulen, 35. Aufl. (2002), S. 42
  20. ^ Alliegro MC, Alliegro MA, Palazzo RE (June 2006). "Centrosome-associated RNA in surf clam oocytes". Proc. Nat. Acad. Sci. USA 103 (24): 9037â9038. doi:10.1073/pnas.0602859103. PMID 16754862. 
  21. ^ Frey-Wyssling, A (1978). "Definition of the organell concept" (in German). Gegenbaurs morphologisches Jahrbuch 124 (3): 455â7. ISSN 0016-5840. PMID 689352. 
  22. ^ Albert Frey-Wyssling: Concerning the concept "Organelle". Experientia 34, 547 (1978). doi:10.1007/BF01935984
  23. ^ Keeling, Pj; Archibald, Jm (April 2008). "Organelle evolution: what's in a name?". Current biology : CB 18 (8): R345â7. doi:10.1016/j.cub.2008.02.065. PMID 18430636. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRT-4SB9SNV-K&_user=5731894&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_userid=5731894&md5=2f16ed5ee031ea9cdce4f7e2a934a8fa. Retrieved 2008-08-07. 
  24. ^ Imanian B, Carpenter KJ, Keeling PJ (March 2007). "Mitochondrial genome of a tertiary endosymbiont retains genes for electron transport proteins.". The Journal of eukaryotic microbiology 54 (2): 146â53. doi:10.1111/j.1550-7408.2007.00245.x. PMID 17403155. http://www3.interscience.wiley.com/cgi-bin/fulltext/118000427/HTMLSTART. 
  25. ^ Mullins, Christopher (2004). "Theory of Organelle Biogenesis: A Historical Perspective". The Biogenesis of Cellular Organelles. Springer Science+Business Media, National Institutes of Health. ISBN 0306479907. 
  26. ^ Campbell and Reece, Biology6th edition, Benjamin Cummings, 2002
  27. ^ Cormack, Introduction to Histology, Lippincott, 1984
  28. ^ Fahey RC, Newton GL, Arrack B, Overdank-Bogart T, Baley S (1984). "Entamoeba histolytica: a eukaryote without glutathione metabolism". Science 224 (4644): 70â72. doi:10.1126/science.6322306. PMID 6322306. 
  29. ^ Badano, Jose L.; Norimasa Mitsuma, Phil L. Beales, Nicholas Katsanis (September 2006). "The Ciliopathies : An Emerging Class of Human Genetic Disorders". Annual Review of Genomics and Human Genetics 7: 125â148. doi:10.1146/annurev.genom.7.080505.115610. PMID 16722803. http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.genom.7.080505.115610. Retrieved 2008-06-15. 
  30. ^ Tsai Y, Sawaya MR, Cannon GC, Cai F, Williams EB, Heinhorst S, Kerfeld CA, Yeates TO (Jun 2007). "Structural analysis of CsoS1A and the protein shell of the Halothiobacillus neapolitanus carboxysome." (Free full text). PLoS biology 5 (6): e144. doi:10.1371/journal.pbio.0050144. PMID 17518518. PMC 1872035. http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050144. 
  31. ^ Ryter A (1988). "Contribution of new cryomethods to a better knowledge of bacterial anatomy". Ann. Inst. Pasteur Microbiol. 139 (1): 33â44. doi:10.1016/0769-2609(88)90095-6. PMID 3289587. 
  32. ^ Komeili A, Li Z, Newman DK, Jensen GJ (2006). "Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK". Science 311 (5758): 242â5. doi:10.1126/science.1123231. PMID 16373532. 
  33. ^ Scheffel A, Gruska M, Faivre D, Linaroudis A, Plitzko JM, Schüler D (2006). "An acidic protein aligns magnetosomes along a filamentous structure in magnetotactic bacteria". Nature 440 (7080): 110â4. doi:10.1038/nature04382. PMID 16299495. 
  34. ^ Fuerst JA (2005). "Intracellular compartmentation in planctomycetes". Annu. Rev. Microbiol. 59: 299â328. doi:10.1146/annurev.micro.59.030804.121258. PMID 15910279. 
  35. ^ Cedano, J., Aloy, P., P'erez-Pons, J. A. & Querol, E. (1997). Relation between amino acid composition and cellular location of proteins. J. Mol. Biol 266, 594-600.
  36. ^ Chou, K. C. & Elrod, D. W. (1999). Protein subcellular location prediction. Protein Engineering 12, 107-118.
  37. ^ Kuo-Chen Chou (2001) Prediction of protein cellular attributes using pseudo amino acid composition. PROTEINS: Structure, Function, and Genetics (Erratum: ibid., 2001, Vol.44, 60) 43, 246-255.
  38. ^ Mundra, P., Kumar, M., Kumar, K. K., Jayaraman, V. K. & Kulkarni, B. D. (2007). Using pseudo amino acid composition to predict protein subnuclear localization: Approached with PSSM. Pattern Recognition Letters 28, 1610-1615.
  39. ^ Du, P., Cao, S. & Li, Y. (2009). SubChlo: predicting protein subchloroplast locations with pseudo-amino acid composition and the evidence-theoretic K-nearest neighbor (ET-KNN) algorithm. Journal of Theoretical Biolology 261, 330-335.
  40. ^ Li, F. M. & Li, Q. Z. (2008). Predicting protein subcellular location using Chou's pseudo amino acid composition and improved hybrid approach. Protein & Peptide Letters 15, 612-616.

[edit] Bibliography

  • Alberts, Bruce et al. (2003). Essential Cell Biology, 2nd ed., Garland Science, 2003, ISBN 081533480X.
  • Alberts, Bruce et al. (2002). The Molecular Biology of the Cell, 4th ed., Garland Science, 2002, ISBN 0-8153-3218-1.

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