My watch list
my.bionity.com  
Login  

Organelle



In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is separately enclosed within its own lipid membrane.  

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 the eukaryotic cells of higher organisms. Prokaryotes were once thought not to have organelles, but some examples have now been identified.[1]

Additional recommended knowledge

Contents

History and Terminology

In biology, an organ is defined as a confined functional unit within an organism. 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[2][3][4] to use a diminutive of organ for respective cellular structures was German zoologist Karl August Möbius (1884), who used the term "organula" [5] (plural from 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,[6] Edmund Wilson[7] and Oscar Hertwig[8] 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".[9]

Around 1920, the term organelle was used to describe propulsion structures ("motor organelle complex", i.e., flagella and their anchoring)[10] and other protist structures, such as ciliates.[11] 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.[12]

In his 1953 textbook, Max Hartmann used the term for extracellular (pellicula, shells, cell walls) and intracellular skeletons of protists.[13]

Later, the now-widely-used[14][15][16][17] 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.[18][19]

In 1978, Albert Frey-Wyssling suggested that the term organelle should refer only to structures that convert energy, such as centrosomes, ribosomes, and nucleoli.[20][21] This new definition, however, did not win wide recognition.

Examples

Whereas 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.

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).

Not all parts of the cell qualify as organelles, and the use of the term to refer to some structures is disputed. These structures are large assemblies of macromolecules that carry out particular and specialized functions, but they lack membrane boundaries. Such cell structures, which are not formally organelles, include:

Eukaryotic organelles

Eukaryotes are 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 species of cells do not have some organelles that might otherwise be considered universal to eukaryotes (such as mitochondria[22]). 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)photosynthesisdouble-membrane compartmentplants, protistshas some genes
endoplasmic reticulumtranslation and folding of new proteins (rough endoplasmic reticulum), expression of lipids (smooth endoplasmic reticulum)single-membrane compartmentall eukaryotesrough endoplasmic reticulum is covered with ribosomes, has folds that are flat sacs; smooth endoplasmic reticulum has folds that are tubular
Golgi apparatussorting and modification of proteinssingle-membrane compartmentall eukaryotescis-face (convex) nearest to rough endoplasmic reticulum; trans-face (concave) farthest from rough endoplasmic reticulum
mitochondrionenergy productiondouble-membrane compartmentmost eukaryoteshas some DNA
vacuolestorage, homeostasissingle-membrane compartmenteukaryotes
nucleusDNA maintenance, RNA transcriptiondouble-membrane compartmentall 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
acrosomehelps spermatoza fuse with ovumsingle-membrane compartmentmany animals
autophagosomevesicle which sequesters cytoplasmic material and organelles for degradationdouble-membrane compartmentall eukaryotic cells
centrioleanchor for cytoskeletonMicrotubule proteinanimals
ciliummovement in or of external mediumMicrotubule proteinanimals, protists, few plants
glycosomecarries out glycolysissingle-membrane compartmentSome protozoa, such as Trypanosomes.
glyoxysomeconversion of fat into sugarssingle-membrane compartmentplants
hydrogenosomeenergy & hydrogen productiondouble-membrane compartmenta few unicellular eukaryotes
lysosomebreakdown of large molecules (e.g., proteins + polysaccharides)single-membrane compartmentmost eukaryotes
melanosomepigment storagesingle-membrane compartmentanimals
mitosomenot characterizeddouble-membrane compartmenta few unicellular eukaryotes
myofibrilmuscular contractionbundled filamentsanimals
nucleolusribosome productionprotein-DNA-RNAmost eukaryotes
parenthesomenot characterizednot characterizedfungi
peroxisomebreakdown of metabolic hydrogen peroxidesingle-membrane compartmentall eukaryotes
ribosometranslation of RNA into proteinsRNA-protein eukaryotes, prokaryotes
vesiclematerial transportsingle-membrane compartmentall eukaryotes

Other related structures:

Prokaryotic organelles

Prokaryotes are not as structurally or metabolically 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. One contributing discovery revealed that at least some prokaryotes have microcompartments, which are compartments enclosed by proteins.[1] Even more striking is the description of magnetosomes,[23][24] as well as the nucleus-like structures of the Planctomycetes that are surrounded by lipid membranes.[25]

Prokaryotic organelles and cell components
Organelle/Macromolecule Main function Structure Organisms
carboxysomecarbon fixationprotein-shell compartmentsome bacteria
chlorosomephotosynthesislight harvesting complexgreen sulfur bacteria
flagellummovement in external mediumprotein filamentsome prokaryotes and eukaryotes
magnetosomemagnetic orientationinorganic crystal, lipid membranemagnetotactic bacteria
nucleoidDNA maintenance, transcription to RNADNA-proteinprokaryotes
plasmidDNA exchangecircular DNAsome bacteria
ribosometranslation of RNA into proteinsRNA-protein eukaryotes, prokaryotes
thylakoidphotosynthesisphotosystem proteins and pigmentsmostly cyanobacteria

See also

References

  1. ^ a b Kerfeld CA, Sawaya MR, Tanaka S, et al (2005). "Protein structures forming the shell of primitive bacterial organelles". Science 309 (5736): 936-8. PMID 16081736.
  2. ^ 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., 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).” 
  3. ^ Amer. Naturalist. 23, 1889, S. 183: „It 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.“ Cited after : Oxford English Dictionary online, entry for „organelle“.
  4. ^ 'Journal de l'anatomie et de la physiologie normales et pathologiques de l'homme et des animaux' at Google Books
  5. ^ Möbius, K. (September 1884). "Das Sterben der einzelligen und der vielzelligen Tiere. Vergleichend betrachtet". Biologisches Centralblatt 4 (13,14): 389 - 392, 448. “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 „Organula“ zu nennen”
  6. ^ Häcker, Valentin (1899). Zellen- und Befruchtungslehre. Jena: Verlag von Gustav Fisher. 
  7. ^ Wilson, Edmund B. (1900). The cell in Development and Inheritance, second edition, New York: The Macmillan Company. 
  8. ^ Hertwig, Oscar (1906). Allgemeine Biologie. Zweite Auflage des Lehrbuchs „Die Zelle und die Gewebe“. Jena: Verlag von Gustav Fischer. 
  9. ^ Lidforss, B. (1915). "Protoplasma", in Paul Hinneberg: Allgemeine Biologie. Leipzig, Berlin: Verlag von B.G.Teubner, 227 (218-264). “Eine Neubildung dieser Organe oder Organellen findet wenigstens bei höheren Pflanzen nicht statt” 
  10. ^ KOFOID, CHARLES ATWOOD; OLIVE SWEZY (1919). "FLAGELLATE AFFINITIES OF TRICHONYMPHA". Proc. Nat. Acad. Sci. USA 5 (1): 9-16.
  11. ^ Cl. Hamburger, Handwörterbuch der Naturw. Bd. V, .S. 435. Infusorien. cited after Petersen, Hans (1919). "Über den Begriff des Lebens und die Stufen der biologischen Begriffsbildung". Archiv für Entwicklungsmechanik der Organismen (now: Development Genes and Evolution) 45 (3): 423-442. doi:10.1007/BF02554406.
  12. ^ 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: 259-327. doi:10.1007/BF02554424. “die Alternative: Organell oder Produkt der Strukturbildung”
  13. ^ Hartmann, Max (1953). Allgemeine Biologie, 4. Aufl., Stuttgart: Gustav Fisher Verlag. 
  14. ^ Nultsch, Allgemeine Botanik, 11. Aufl. 2001, Thieme Verlag
  15. ^ Wehner/Gehring, Zoologie, 23. Aufl. 1995, Thieme Verlag
  16. ^ Alberts et al., Molecular Biology of the Cell, 4. ed. 2002, online via "NCBI-Bookshelf"
  17. ^ Brock, Mikrobiologie, 2. korrigierter Nachdruck (2003), der 1. Aufl. von 2001
  18. ^ Strasburgers Lehrbuch der Botanik für Hochschulen, 35. Aufl. (2002), S. 42
  19. ^ Alliegro, Mark C.; Mary Anne Alliegro and Robert E. Palazzo (June 13, 2006). "Centrosome-associated RNA in surf clam oocytes". Proc. Nat. Acad. Sci. USA 103 (24): 9034-9038. doi:10.1073/pnas.0602859103.
  20. ^ Albert Frey-Wyssling (1978). "Zur Definition des Organell-Begriffes". Gegenbaurs morphologisches Jahrbuch, Leipzig 124 (3): 455-57.
  21. ^ Albert Frey-Wyssling: Concerning the concept "Organelle". Experientia 34, 547 (1978). doi:10.1007/BF01935984 The journal's new name is Cellular and Molecular Life Sciences.
  22. ^ Fahey RC, Newton GL, Arrack B, Overdank-Bogart T, Baley S (1984). "Entamoeba histolytica: a eukaryote without glutathione metabolism". Science 224 (4644): 70-72. PMID 6322306.
  23. ^ Komeili A, Li Z, Newman DK, Jensen GJ (2006). "Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK". Science 311 (5758): 242-5. PMID 16373532.
  24. ^ 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): 110-4. PMID 16299495.
  25. ^ Fuerst JA (2005). "Intracellular compartmentation in planctomycetes". Annu. Rev. Microbiol. 59: 299-328. PMID 15910279.
  • 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.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Organelle". A list of authors is available in Wikipedia.
Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE