Editing Nucleoside triphosphate (section)

=== Pyrimidine synthesis ===
A nitrogenous base called [[orotate]] is synthesized independently of PRPP.<ref name="Nierlich_1965" /> After orotate is made it is covalently attached to PRPP. This results in a nucleotide called orotate monophosphate (OMP).<ref>{{cite journal | vauthors = Moffatt BA, Ashihara H | title = Purine and pyrimidine nucleotide synthesis and metabolism | journal = The Arabidopsis Book | volume = 1 | pages = e0018 | date = April 2002 | pmid = 22303196 | pmc = 3243375 | doi = 10.1199/tab.0018 }}</ref> OMP is converted to UMP, which can then be phosphorylated by ATP to UDP and UTP. UTP can then be converted to CTP by a [[deamination]] reaction.<ref>{{cite web|url=https://www.cliffsnotes.com/study-guides/biology/biochemistry-ii/purines-and-pyrimidines/pyrimidine-metabolism|title=Pyrimidine Metabolism|website=www.cliffsnotes.com|access-date=2017-11-15}}</ref> TTP is not a substrate for nucleic acid synthesis, so it is not synthesized in the cell. Instead, dTTP is made indirectly from either dUDP or dCDP after conversion to their respective deoxyribose forms.<ref name=":5" />

Pyrimidine synthesis is regulated by the allosteric inhibition of orotate synthesis by UDP and UTP. PRPP and ATP are also allosteric activators of orotate synthesis.<ref>{{cite journal | vauthors = Lane AN, Fan TW | title = Regulation of mammalian nucleotide metabolism and biosynthesis | journal = Nucleic Acids Research | volume = 43 | issue = 4 | pages = 2466–85 | date = February 2015 | pmid = 25628363 | doi = 10.1093/nar/gkv047 | pmc=4344498}}</ref>