<P> In vitro, protecting groups may be used during laboratory production of nucleotides . A purified nucleoside is protected to create a phosphoramidite, which can then be used to obtain analogues not found in nature and / or to synthesize an oligonucleotide . </P> <P> The synthesis of the pyrimidines CTP and UTP occurs in the cytoplasm and starts with the formation of carbamoyl phosphate from glutamine and CO . Next, aspartate carbamoyltransferase catalyzes a condensation reaction between aspartate and carbamoyl phosphate to form carbamoyl aspartic acid, which is cyclized into 4, 5 - dihydroorotic acid by dihydroorotase . The latter is converted to orotate by dihydroorotate oxidase . The net reaction is: </P> <Dl> <Dd> (S) - Dihydroorotate + O → Orotate + H O </Dd> </Dl> <Dd> (S) - Dihydroorotate + O → Orotate + H O </Dd>

What are the common parts of a nucleutide