organized cell-level biological structure of distinctive morphology and function
(Redirected from Organelles)

In cell biology, an organelle is a part of a cell that does a specific job.

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.

Organelles usually have a plasma membrane around them.[1] Most of the cell's organelles are in the cytoplasm.[2][3]

The name organelle comes from the idea that these structures are to cells what an organ is to the body.

There are many types of organelles in eukaryotic cells. Prokaryotes were once thought not to have organelles, but some examples have now been found.[4] They are not organized like eukaryote organelles, and are not bounded by plasma membranes. They are called bacterial microcompartments.[5]

Scope of the term


The term is now widely used to refer to cell structures surrounded by single or double plasma membranes.[6][7][8][9] However, the older definition of a 'subcellular functional unit' still exists. So, the term is sometimes used for structures which are not membrane-bound.[10][11]

The plasma membrane is a lipid bilayer with some proteins embedded in it. It keeps the ions and molecules of the organelle from merging with the surroundings.

Origin of organelles


Mitochondria and chloroplasts have double-membranes and their DNA. These are believed to come from incompletely digested or invading prokaryotes, which were adopted as a part of the invaded cell. This idea is supported in the endosymbiotic theory.

Eukaryotic organelles


Major organelles

Major eukaryotic organelles
Organelle Main function Structure Organisms Notes
chloroplast (plastid) photosynthesis double-membrane compartment plants, protists has some DNA; originally obtained from 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 has many ribosomes, and folds that are flat sacs; smooth endoplasmic reticulum has folds that are tubular
flagellum locomotion, sensory some eukaryotes
Golgi apparatus sorting and modification of proteins single-membrane compartment all eukaryotes
mitochondrion energy production double-membrane compartment most eukaryotes has some DNA; originally obtained by endosymbiosis
nucleus DNA maintenance, RNA transcription double-membrane compartment all eukaryotes has bulk of genome
vacuole storage, homeostasis single-membrane compartment eukaryotes

Minor organelles

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 collects 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. microtubule protein animals, protists, few plants
cnidocyst stinging coiled hollow tubule cnidarians
eyespot apparatus detects light, allowing phototaxis to take place green algae and other unicellular photosynthetic organisms such as Euglena
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 by convention, animal cells; but (wider definition) most eukaryotes
melanosome pigment storage single-membrane compartment animals
mitosome not known double-membrane compartment a few unicellular eukaryotes
myofibril muscular contraction bundled filaments animals
nucleolus ribosome production protein-DNA-RNA most eukaryotes
parenthesome not known not known fungi
peroxisome breakdown of metabolic hydrogen peroxide single-membrane compartment all eukaryotes
proteasome degradation of unneeded or damaged proteins by proteolysis very large protein complex All eukaryotes, all archaea, some bacteria
ribosome translation of RNA into proteins RNA-protein eukaryotes, prokaryotes
stress granule mRNA storage membraneless (mRNP complexes) Most eukaryotes
vesicle material transport single-membrane compartment all eukaryotes

Prokaryotic organelles


Prokaryotes are not so complex as eukaryotes. They were once thought to have no internal structures inside the lipid membranes.[12]

However, recent research has shown 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.[13] Even more striking is the description of membrane-bound magnetosomes in bacteria.[14][15] as well as the nucleus-like structures of the Planctomycetes that are surrounded by lipid membranes.[16]

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


  1. See 'Scope of the term' below.
  2. Alberts, Bruce et al. 2003. Essential cell biology, 2nd ed. Garland Science.
  3. National Research Council (U.S.). Committee on Research Opportunities in Biology (1989). Opportunities in biology. National Academies. p. 104. ISBN 978-0-309-03927-7. Retrieved 23 December 2010.
  4. Kerfeld C.; et al. (2005). "Protein structures forming the shell of primitive bacterial organelles". Science. 309 (5736): 936–8. Bibcode:2005Sci...309..936K. doi:10.1126/science.1113397. PMID 16081736. S2CID 24561197.
  5. Bobik T.A. (2007). "Bacterial microcompartments" (PDF). Microbe. 2. Am Soc Microbiol: 25–31. Archived from the original (PDF) on 2008-08-02. Retrieved 2011-01-06.
  6. Nultsch, Allgemeine Botanik, 11 Aufl. 2001, Thieme Verlag
  7. Wehner/Gehring: Zoologies. 23. Aufl. 1995, Thieme Verlag
  8. Alberts, Bruce (2004). Molecular Biology of the Cell. ISBN 978-0-8153-3218-3.
  9. Brock, Microbiology, 2. korrigierter Nachdruck 2003. der 1. Aufl. von 2001
  10. Strasburger's Lehrbuch der Botanik für Hochschulen, 35. Aufl. 2002. S. 42
  11. Alliegro MC, Alliegro MA, Palazzo RE (2006). "Centrosome-associated RNA in surf clam oocytes". Proc. Nat. Acad. Sci. USA. 103 (24): 9037–9038. Bibcode:2006PNAS..103.9034A. doi:10.1073/pnas.0602859103. PMC 1482561. PMID 16754862.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. Ryter A (1988). "Contribution of new cryomethods to a better knowledge of bacterial anatomy". Ann. Inst. Pasteur Microbiol. 139 (1): 33–44. doi:10.1016/0769-2609(88)90095-6. PMID 3289587.
  13. Kerfeld CA; et al. (2005). "Protein structures forming the shell of primitive bacterial organelles". Science. 309 (5736): 936–8. Bibcode:2005Sci...309..936K. doi:10.1126/science.1113397. PMID 16081736. S2CID 24561197.
  14. Komeili A.; et al. (2006). "Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK". Science. 311 (5758): 242–5. Bibcode:2006Sci...311..242K. doi:10.1126/science.1123231. PMID 16373532. S2CID 36909813.
  15. Scheffel A.; et al. (2006). "An acidic protein aligns magnetosomes along a filamentous structure in magnetotactic bacteria". Nature. 440 (7080): 110–4. Bibcode:2006Natur.440..110S. doi:10.1038/nature04382. PMID 16299495. S2CID 4372846.
  16. Fuerst JA (2005). "Intracellular compartmentation in planctomycetes". Annu. Rev. Microbiol. 59: 299–328. doi:10.1146/annurev.micro.59.030804.121258. PMID 15910279.