Editing Nucleotide base (section)

==Modified nucleobases==
DNA and RNA also contain other (non-primary) bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is [[5-methylcytosine]] (m<sup>5</sup>C). In RNA, there are many modified bases, including those contained in the nucleosides [[pseudouridine]] (Ψ), [[dihydrouridine]] (D), [[inosine]] (I), and [[7-methylguanosine]] (m<sup>7</sup>G).<ref>{{cite web |last1=Stavely |first1=Brian E. |title=BIOL2060: Translation |url=https://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-22/CB22.html |website=www.mun.ca |access-date=17 August 2020}}</ref><ref>[http://www.biogeo.uw.edu.pl/research/grupaC_en.html "Role of 5' mRNA and 5' U snRNA cap structures in regulation of gene expression"] – Research – Retrieved 13 December 2010.</ref>

[[Hypoxanthine]] and [[xanthine]] are two of the many bases created through [[mutagen]] presence, both of them through [[deamination]] (replacement of the amine-group with a carbonyl-group). Hypoxanthine is produced from adenine, xanthine from guanine,<ref name="pmid1557408">{{cite journal | vauthors = Nguyen T, Brunson D, Crespi CL, Penman BW, Wishnok JS, Tannenbaum SR | title = DNA damage and mutation in human cells exposed to nitric oxide in vitro | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 89 | issue = 7 | pages = 3030–4 | date = April 1992 | pmid = 1557408 | pmc = 48797 | doi = 10.1073/pnas.89.7.3030 | bibcode = 1992PNAS...89.3030N | doi-access = free }}</ref> and uracil results from deamination of cytosine.

===Modified purine nucleobases===
These are examples of modified adenosine or guanosine.
{| class="wikitable skin-invert-image"
|- align="center" valign="bottom"
| '''Nucleobase'''|| [[File:Hypoxanthin.svg|70px|Chemical structure of hypoxanthine]]<br />[[Hypoxanthine]]|| [[File:Xanthin.svg|75px|Chemical structure of xanthine]]<br />[[Xanthine]]|| [[File:7methylguanine.svg|93px|Chemical structure of 7-methylguanine]]<br />[[7-Methylguanine]]
|- align="center" valign="bottom"
| '''Nucleoside'''|| [[File:Inosin.svg|95px|Chemical structure of inosine]]<br />[[Inosine]]<br />I || [[File:Xanthosin.svg|105px|Chemical structure of xanthosine]]<br />[[Xanthosine]]<br />X || [[File:7-Methylguanosine.svg|140px|Chemical structure of 7-methylguanosine]]<br />[[7-Methylguanosine]]<br />m<sup>7</sup>G
|}

===Modified pyrimidine nucleobases===
These are examples of modified cytidine, thymidine or uridine.
{| class="wikitable skin-invert-image"
|- align="center" valign="bottom"
| '''Nucleobase'''|| [[File:Dihydrouracil.svg|55px|Chemical structure of dihydrouracil]]<br />[[5,6-Dihydrouracil]]|| [[File:5-Methylcytosine.svg|75px|Chemical structure of 5-methylcytosine]]<br />[[5-Methylcytosine]]|| [[File:Hydroxymethylcytosine.png|60px|Chemical structure of 5-hydroxymethylcytosine]]<br />[[5-Hydroxymethylcytosine]]
|- align="center" valign="bottom"
| '''Nucleoside'''|| [[File:Dihydrouridine.svg|87px|Chemical structure of dihydrouridine]]<br />[[Dihydrouridine]]<br />D || [[File:5-Methylcytidine.svg|87px|Chemical structure of 5-methylcytidine]]<br />[[5-Methylcytidine]]<br />m<sup>5</sup>C ||[[File:Pseudouridine.svg|87px]]<br />[[Pseudouridine]]
|}