Editing Pyrimidine (section)

=== Nucleotides ===
[[File:Blausen 0324 DNA Pyrimidines.png|thumb|250px|The pyrimidine nitrogen bases found in [[DNA]] and [[RNA]].]]
Three [[nucleobase]]s found in [[nucleic acid]]s, [[cytosine]] (C), [[thymine]] (T), and [[uracil]] (U), are pyrimidine derivatives:
:{|
|-
| [[Image:Cytosine chemical structure.png|left|101px|class=skin-invert-image|Chemical structure of cytosine]] || [[Image:Thymine chemical structure.png|left|127px|class=skin-invert-image|Chemical structure of thymine]] || [[Image:Uracil chemical structure.png|left|102px|class=skin-invert-image|Chemical structure of uracil]]
|-
| {{center|Cytosine ('''C''')}} || {{center|Thymine ('''T''')}} || {{center|Uracil ('''U''')}}
|}

In [[DNA]] and [[RNA]], these bases form [[hydrogen bond]]s with their [[complementarity (molecular biology)|complementary]] [[purine]]s. Thus, in DNA, the [[purines]] [[adenine]] (A) and [[guanine]] (G) pair up with the pyrimidines thymine (T) and cytosine (C), respectively.

In [[RNA]], the complement of [[adenine]] (A) is [[uracil]] (U) instead of [[thymine]] (T), so the pairs that form are [[adenine]]:[[uracil]] and [[guanine]]:[[cytosine]].

Very rarely, thymine can appear in RNA, or uracil in DNA, but when the other three major pyrimidine bases are represented, some minor pyrimidine bases can also occur in [[nucleic acids]]. These minor pyrimidines are usually [[Methylation|methylated]] versions of major ones and are postulated to have regulatory functions.<ref>{{cite book|last1=Nelson |first1=David L. |first2=Michael M. |last2=Cox |title=Principles of Biochemistry |edition=5th |publisher=W. H. Freeman |date=2008 |pages=272–274 |isbn=978-1429208925}}</ref>

These hydrogen bonding modes are for classical Watson–Crick [[base pair]]ing. Other hydrogen bonding modes ("wobble pairings") are available in both DNA and RNA, although the additional 2′-hydroxyl group of [[RNA]] expands the configurations, through which RNA can form hydrogen bonds.<ref>{{Cite journal|last1=PATIL|first1=SHARANABASAPPA B.|last2=P.|first2=GOURAMMA|last3=JALDE|first3=SHIVAKUMAR S.|title=Medicinal Significance of Novel Coumarins: A Review|date=2021-07-15|journal=International Journal of Current Pharmaceutical Research|pages=1–5|doi=10.22159/ijcpr.2021v13i4.42733|s2cid=238840705|issn=0975-7066|doi-access=free}}</ref>