Editing Organelle (section)

== Types ==
While most cell biologists consider the term ''organelle'' to be synonymous with [[cell compartment]], a space often bounded by one or two lipid bilayers, some cell biologists choose to limit the term to include only those cell compartments that contain [[DNA|deoxyribonucleic acid]] (DNA), having originated from formerly autonomous microscopic organisms acquired via [[endosymbiosis]].<ref name=organelleEvolution2008/>

The first, broader conception of organelles is that they are membrane-bounded structures. However, even by using this definition, some parts of the cell that have been shown to be distinct functional units do not qualify as organelles. Therefore, the use of organelle to also refer to non-membrane bounded structures such as ribosomes is common and accepted.<ref>{{cite book | first1 = Neil A | last1 = Campbell | first2 = Jane B | last2 = Reece | first3 = Lawrence G | last3 = Mitchell | name-list-style = vanc | title = Biology | edition = 6th | publisher = Benjamin Cummings | date = 2002 | isbn = 978-0-8053-6624-2 | url-access = registration | url = https://archive.org/details/biologyc00camp }}</ref>{{Verify source|date=September 2022}}<ref>{{cite journal | vauthors = Nott TJ, Petsalaki E, Farber P, Jervis D, Fussner E, Plochowietz A, Craggs TD, Bazett-Jones DP, Pawson T, Forman-Kay JD, Baldwin AJ | title = Phase transition of a disordered nuage protein generates environmentally responsive membraneless organelles | journal = Molecular Cell | volume = 57 | issue = 5 | pages = 936–947 | date = March 2015 | pmid = 25747659 | pmc = 4352761 | doi = 10.1016/j.molcel.2015.01.013 }}</ref><ref>{{cite journal | vauthors = Banani SF, Lee HO, Hyman AA, Rosen MK | title = Biomolecular condensates: organizers of cellular biochemistry | journal = Nature Reviews Molecular Cell Biology | volume = 18 | issue = 5 | pages = 285–298 | date = May 2017 | pmid = 28225081 | doi = 10.1038/nrm.2017.7 | pmc = 7434221 }}</ref> 

This has led many texts to delineate between '''membrane-bounded''' and '''non-membrane''' bounded organelles.<ref>{{cite book | vauthors = Cormack DH | title = Introduction to Histology | date = 1984 | publisher = Lippincott | isbn = 978-0-397-52114-2 | url-access = registration | url = https://archive.org/details/unset0000unse_d5o8 }}</ref> The non-membrane bounded organelles, also called large [[biomolecular complex]]es, are large assemblies of [[macromolecule]]s that carry out particular and specialized functions, but they lack membrane boundaries.  Many of these are referred to as "proteinaceous organelles" as their main structure is made of proteins. Such cell structures include:
* large RNA and protein complexes: [[ribosome]], [[spliceosome]], [[vault (organelle)|vault]]
* large [[protein complex]]es: [[proteasome]], [[DNA polymerase III holoenzyme]], [[RNA polymerase II holoenzyme]], symmetric viral [[capsid]]s, complex of [[GroEL]] and [[GroES]]; membrane protein complexes: [[porosome]], [[photosystem I]], [[ATP synthase]]
* large DNA and protein complexes: [[nucleosome]]
* [[centriole]] and [[microtubule-organizing center]] (MTOC)
* [[cytoskeleton]]
* [[flagellum]]
* [[nucleolus]]
* [[stress granule]]
* [[germ cell]] granule
* neuronal transport granule

The mechanisms by which such non-membrane bounded organelles form and retain their spatial integrity have been likened to liquid-liquid [[phase separation]].<ref>{{cite journal | vauthors = Brangwynne CP, Eckmann CR, Courson DS, Rybarska A, Hoege C, Gharakhani J, Jülicher F, Hyman AA | title = Germline P granules are liquid droplets that localize by controlled dissolution/condensation | journal = Science | volume = 324 | issue = 5935 | pages = 1729–32 | date = June 2009 | pmid = 19460965 | doi = 10.1126/science.1172046 | bibcode = 2009Sci...324.1729B | s2cid = 42229928 | doi-access = free }}</ref>

The second, more restrictive definition of organelle includes only those cell compartments that contain [[DNA|deoxyribonucleic acid]] (DNA), having originated from formerly autonomous microscopic organisms acquired via [[endosymbiosis]].<ref name=organelleEvolution2008>{{cite journal | vauthors = Keeling PJ, Archibald JM | title = Organelle evolution: what's in a name? | journal = Current Biology | volume = 18 | issue = 8 | pages = R345-7 | date = April 2008 | pmid = 18430636 | doi = 10.1016/j.cub.2008.02.065 | s2cid = 11520942 | doi-access = free | bibcode = 2008CBio...18.R345K }}</ref><ref>{{cite journal | vauthors = Imanian B, Carpenter KJ, Keeling PJ | title = Mitochondrial genome of a tertiary endosymbiont retains genes for electron transport proteins | journal = The Journal of Eukaryotic Microbiology | volume = 54 | issue = 2 | pages = 146–53 | date = March–April 2007 | pmid = 17403155 | doi = 10.1111/j.1550-7408.2007.00245.x | s2cid = 20393495 }}</ref><ref>{{cite book |last=Mullins |first=Christopher | name-list-style = vanc |author-link=Christopher Mullins |title=The Biogenesis of Cellular Organelles |chapter=Theory of Organelle Biogenesis: A Historical Perspective |year=2004 |publisher=[[Springer Science+Business Media]], [[National Institutes of Health]] |isbn=978-0-306-47990-8}}</ref>

Using this definition, there would only be two broad classes of organelles (i.e. those that contain their own DNA, and have originated from endosymbiotic [[bacterium|bacteria]]):
* [[mitochondrion|mitochondria]] (in almost all eukaryotes)
* [[plastid]]s<ref>{{cite book | first1 = Bruce | last1 = Alberts | first2 = Alexander | last2 = Johnson | first3 = Julian | last3 = Lewis | first4 = Martin | last4 = Raff | first5 = Keith | last5 = Roberts | first6 = Peter | last6 = Walter | name-list-style = vanc |  chapter = The Genetic Systems of Mitochondria and Plastids | chapter-url = https://www.ncbi.nlm.nih.gov/books/NBK26924/ | title = Molecular Biology of the Cell | year = 2002 | edition = 4th | isbn = 978-0-8153-3218-3 }}</ref> (e.g. in plants, algae, and some protists).

Other organelles are also suggested{{by whom|date=February 2023}} to have endosymbiotic origins, but do not contain their own DNA{{citation needed|date=February 2023}} (notably the flagellum – see [[evolution of flagella]]).