Editing Euchromatin (section)

== Structure ==
Euchromatin is composed of repeating subunits known as [[nucleosome]]s, reminiscent of an unfolded set of beads on a string, that are approximately 11&nbsp;nm in diameter.<ref name="Babu_1987">{{cite journal | vauthors = Babu A, Verma RS | title = Chromosome structure: euchromatin and heterochromatin | journal = International Review of Cytology | volume = 108 | pages = 1–60 | date = January 1987 | pmid = 2822591 | doi = 10.1016/s0074-7696(08)61435-7 | publisher = Academic Press | isbn = 978-0-12-364508-1 | veditors = Bourne GH, Jeon KW, Friedlander M }}</ref> At the core of these nucleosomes are a set of four [[histone]] protein pairs: [[Histone H3|H3]], [[Histone H4|H4]], [[Histone H2A|H2A]], and [[Histone H2B|H2B]].<ref name="Babu_1987" /> Each core histone protein possesses a 'tail' structure, which can vary in several ways; it is thought that these variations act as "master control switches" through different [[methylation]] and [[acetylation]] states, which determine the overall arrangement of the chromatin.<ref name="Babu_1987" /> Approximately 147 base pairs of [[DNA]] are wound around the histone octamers, or a little less than 2 turns of the helix.<ref>{{Cite web|title= Definition: nucleosome/nucleosomes | work = Scitable Nature Education |url=https://www.nature.com/scitable/definition/nucleosome-nucleosomes-30/|access-date=2021-10-06 |language=en}}</ref> Nucleosomes along the strand are linked together via the histone, [[Histone H1|H1]],<ref>{{cite book | vauthors = Mobley AS | chapter = Chapter 4 - Induced Pluripotent Stem Cells|date= January 2019 | title =Neural Stem Cells and Adult Neurogenesis|pages=67–94| veditors = Mobley AS |publisher=Academic Press|language=en|isbn=978-0-12-811014-0 }}</ref> and a short space of open [[linker DNA]], ranging from around 0-80 base pairs. The key distinction between the structure of euchromatin and [[heterochromatin]] is that the nucleosomes in euchromatin are much more widely spaced, which allows for easier access of different protein complexes to the DNA strand and thus increased gene [[Transcription (biology)|transcription]].<ref name="Babu_1987" />