Nucleoid 805665 223104576 2008-07-02T16:18:52Z DOI bot 6652755 Citation maintenance. Removed redundant parameters. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. [[Image:Celltypes.png|thumb|330px|right|Prokaryote cell showing the nucleoid.]] In [[prokaryotes]], the '''nucleoid''' (meaning ''nucleus-like'' and also known as the '''nuclear region''', '''nuclear body''' or '''chromatin body''') is an irregularly-shaped region within the [[cell (biology)|cell]] of [[prokaryote]]s where the [[genetic material]] is localized.<ref>{{cite journal |author=Thanbichler M, Wang S, Shapiro L |title=The bacterial nucleoid: a highly organized and dynamic structure |journal=J Cell Biochem |volume=96 |issue=3 |pages=506–21 |year=2005 |pmid=15988757 |doi=10.1002/jcb.20519}}</ref> The nucleic acid is a circular, double-stranded piece of [[DNA]], and multiple copies may exist. This method of genetic storage can be contrasted against that of the [[eukaryote]]s, where DNA is packed into [[chromatin]]s and sequestered within a membrane-enclosed organelle called the [[cell nucleus|nucleus]]. A ''genophore'' is the [[DNA]] of a [[prokaryote]]. This is commonly referred to as a prokaryotic [[chromosome]]. The term chromosome is misleading for a genophore because the genophore lacks [[chromatin]] <ref> Ris, H. (1961). Ultrastructure and molecular organization of genetic systems. Can. J. Genet. Cytol. 3, 95-120.</ref>. The genophore is compacted through a mechanism known as [[supercoiling]]<ref>{{cite journal | author = Benham C, Mielke S | title = DNA mechanics | journal = Annu Rev Biomed Eng | volume = 7 | issue = | pages = 21 – 53 | year = 2005| pmid = 16004565 | doi = 10.1146/annurev.bioeng.6.062403.132016}}</ref>. Where a chromosome is compacted via chromatin. The genophore is circular in most prokaryotes, and linear in very few. The circular nature of the genophore allows replication to occur without [[telomeres]].<ref>{{cite book | author= Nelson D, Cox M | title Principles of Biochemistry Third Edition | pages 28-39 | year = 2000 | ISBN = 1-57259-153-6}}</ref> Genophores are generally of a much smaller size than Eukaryotic chromosomes. A genophore of a true organism can be as small as 580,073 base pairs (Mycoplasma genitalium). Many eukaryotes (such as plants and animals) carry genophores in organelles such as [[mitochondria]] and [[chloroplasts]]. These organelles are very similar to true prokaryotes.<ref>{{cite book | author= Nelson D, Cox M | title Principles of Biochemistry Third Edition | pages 38-39 | year = 2000 | ISBN = 1-57259-153-6}}</ref> ==Visualisation== The nucleoid can be clearly visualised on an [[electron micrograph]] at high magnification, where, although its appearance may differ, it is clearly visible against the [[cytosol]]. Sometimes even strands of what is thought to be DNA are visible. By staining with the [[Feulgen stain]], which specifically stains DNA, the nucleoid can also be seen under a light microscope. The DNA-intercalating stains DAPI and ethidium bromide are widely used for fluorescence microscopy of nucleoids. ==Composition== Experimental evidence suggests that the nucleoid is largely composed of DNA, about 60%, with a small amount of [[RNA]] and [[protein]]. The latter two constituents are likely to be mainly [[messenger RNA]] and the [[transcription factor]] proteins found regulating the bacterial genome. Proteins helping to maintain the supercoiled structure of the nucleic acid are known as ''nucleoid proteins'' or nucleoid associated proteins and are distinct from [[histone]]s of eukaryotic nuclei. In contrast to histones, the DNA-binding proteins of the nucleoid do not form nucleosomes. ==See also== *[[Cell nucleus]] *[[Plasmid]] ==References== {{reflist}} *Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3 {{Organelles}} [[Category:Bacteriology]] [[Category:Cell anatomy]] [[Category:Microbiology]] {{Cell-biology-stub}} [[cs:Nukleoid]] [[de:Kernäquivalent]] [[es:Nucleoide]] [[ko:핵양체]] [[it:Nucleoide]] [[lt:Nukleoidas]] [[pl:Nukleoid]] [[pt:Nucleóide]] [[ru:Нуклеоид]] [[sr:Нуклеоид]] [[sh:Nukleoid]] [[fi:Nukleoidi]] [[uk:Нуклеоїд]] [[zh:拟核]]