Editing Cell nucleus (section)

==Chromosomes==
{{Main|Chromosome}}
{{Further|Nuclear organization}}

[[Image:MouseChromosomeTerritoriesBMC Cell Biol6-44Fig2e.jpg|thumb|200px|A mouse [[fibroblast]] nucleus in which [[DNA]] is stained blue. The distinct chromosome territories of chromosome 2 (red) and chromosome 9 (green) are stained with [[fluorescent in situ hybridization]].]]

The cell nucleus contains the majority of the cell's genetic material in the form of multiple linear DNA molecules organized into structures called [[chromosome]]s. Each human cell contains roughly two meters of DNA.<ref name = "Lodish" />{{rp|405}} During most of the [[cell cycle]] these are organized in a DNA-protein complex known as [[chromatin]], and during cell division the chromatin can be seen to form the well-defined chromosomes familiar from a [[karyotype]]. A small fraction of the cell's genes are located instead in the [[mitochondria]].<ref name = "Lodish" />{{rp|438}}

There are two types of chromatin. [[Euchromatin]] is the less compact DNA form, and contains genes that are frequently [[gene expression|expressed]] by the cell.<ref name="Ehrenhofer">{{cite journal | vauthors = Ehrenhofer-Murray AE | title = Chromatin dynamics at DNA replication, transcription and repair | journal = European Journal of Biochemistry | volume = 271 | issue = 12 | pages = 2335–49 | date = June 2004 | pmid = 15182349 | doi = 10.1111/j.1432-1033.2004.04162.x | department = Review | doi-access = free }}</ref> The other type, [[heterochromatin]], is the more compact form, and contains DNA that is infrequently transcribed. This structure is further categorized into [[Facultative heterochromatin#Facultative heterochromatin|''facultative'' heterochromatin]], consisting of genes that are organized as heterochromatin only in certain cell types or at certain stages of development, and [[Constitutive heterochromatin|''constitutive'' heterochromatin]] that consists of chromosome structural components such as [[telomere]]s and [[centromere]]s.<ref name="Grigoryev">{{cite journal | vauthors = Grigoryev SA, Bulynko YA, Popova EY | title = The end adjusts the means: heterochromatin remodelling during terminal cell differentiation | journal = Chromosome Research | volume = 14 | issue = 1 | pages = 53–69 | year = 2006 | pmid = 16506096 | doi = 10.1007/s10577-005-1021-6 | s2cid = 6040822 | department = Review }}</ref> During interphase the chromatin organizes itself into discrete individual patches,<ref name="Schardin">{{cite journal | vauthors = Schardin M, Cremer T, Hager HD, Lang M | title = Specific staining of human chromosomes in Chinese hamster x man hybrid cell lines demonstrates interphase chromosome territories | journal = Human Genetics | volume = 71 | issue = 4 | pages = 281–7 | date = December 1985 | pmid = 2416668 | doi = 10.1007/BF00388452 | url = https://epub.ub.uni-muenchen.de/9272/1/cremer_thomas_9272.pdf | s2cid = 9261461 | department = Primary }}</ref> called ''[[chromosome territories]]''.<ref name="Lamond">{{cite journal | vauthors = Lamond AI, Earnshaw WC | title = Structure and function in the nucleus | journal = Science | volume = 280 | issue = 5363 | pages = 547–53 | date = April 1998 | pmid = 9554838 | doi = 10.1126/science.280.5363.547 | url = http://azolla.fc.ul.pt/aulas/BiologiaCelular/docs/nucleo.pdf | citeseerx = 10.1.1.323.5543 | department = Review }}</ref> Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.<ref name="Kurz">{{cite journal | vauthors = Kurz A, Lampel S, Nickolenko JE, Bradl J, Benner A, Zirbel RM, Cremer T, Lichter P | display-authors = 6 | title = Active and inactive genes localize preferentially in the periphery of chromosome territories | journal = The Journal of Cell Biology | volume = 135 | issue = 5 | pages = 1195–205 | date = December 1996 | pmid = 8947544 | pmc = 2121085 | doi = 10.1083/jcb.135.5.1195 | url = http://intl.jcb.org/cgi/content/abstract/135/5/1195 | url-status = dead | department = Primary | archive-url = https://web.archive.org/web/20070929104104/http://intl.jcb.org/cgi/content/abstract/135/5/1195 | archive-date = 29 September 2007 }}</ref>

Antibodies to certain types of chromatin organization, in particular, [[nucleosome]]s, have been associated with a number of [[autoimmune disease]]s, such as [[systemic lupus erythematosus]].<ref name="Rothfield">{{cite journal | vauthors = Rothfield NF, Stollar BD | title = The relation of immunoglobulin class, pattern of anti-nuclear antibody, and complement-fixing antibodies to DNA in sera from patients with systemic lupus erythematosus | journal = The Journal of Clinical Investigation | volume = 46 | issue = 11 | pages = 1785–94 | date = November 1967 | pmid = 4168731 | pmc = 292929 | doi = 10.1172/JCI105669 | department = Primary }}</ref> These are known as [[anti-nuclear antibody|anti-nuclear antibodies]] (ANA) and have also been observed in concert with [[multiple sclerosis]] as part of general immune system dysfunction.<ref name="Barned">{{cite journal | vauthors = Barned S, Goodman AD, Mattson DH | title = Frequency of anti-nuclear antibodies in multiple sclerosis | journal = Neurology | volume = 45 | issue = 2 | pages = 384–5 | date = February 1995 | pmid = 7854544 | doi = 10.1212/WNL.45.2.384 | s2cid = 30482028 | department = Primary }}</ref>