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Pyrimidine biosynthesis occurs both in the body and through organic synthesis.

Contents 1 In the body 1.1 De novo biosynthesis of pyrimidine 1.2 Pyrimidine catabolism 2 Organic synthesis 3 External links

Unlike purines, pyrimidines are assembled before being attached to 5-phosphoribosyl-1-pyrophosphate (PRPP).

• The first step begins with formation of carbamoyl phosphate by carbamoyl phosphate synthetase II. This is the regulated step in the pyrimidine biosynthesis.

• The second major step is the creation of carbamoyl aspartic acid formed by aspartic transcarbamolyase (aspartate carbamoyl transferase).

• The next reaction involves dehydration of the acid catalysed by the enzyme dihhydroorotase to form dihydroorotate.

• Dihydroorotate then enters the mitochondria where it is oxidised through removal of hydrogens to form orotate. This is the only mitochondrial step in nucleotide rings biosynthesis. The enzyme involved is dihydroorotate dehydrogenase (the only mitochondrial enzyme).

• Once orotate is eventually formed, it is combined with PRPP to form orotidine 5' -monophosphate (OMP) which is decarboxylated in a reaction catalysed by OMP decarboxylase to form uridine 5'-monophosphate.^{[citation needed]}

• UMP is then converted to UDP catalysed by nucleotide diphosphokinase which is further phosphorylated to UTP by CTP synthase. This later reaction eventually leads to the formation of cytidine 5'triphosphate and glutamine is utilized.^{[citation needed]}

Pyrimidines are ultimately catabolized (degraded) to CO₂, H₂O, and urea. Cytosine can be broken down to uracil which can be further broken down to N-carbamoyl-β-alanine. Thymine is broken down into β-aminoisobutyrate which can be further broken down into intermediates eventually leading into the citric acid cycle. β-aminoisobutyrate acts as a rough indicator for rate of DNA turnover.^{[citation needed]}

Pyrimidines can also be prepared in the laboratory by organic synthesis. Many methods rely on condensation of carbonyls with amines for instance the synthesis of 2-Thio-6-methyluracil from thiourea and ethyl acetoacetate ^[1] or the synthesis of 4-methylpyrimidine with 4,4-dimethoxy-2-butanone and formamide ^[2].

A novel method is by reaction of certain amides with carbonitriles under electrophilic activation of the amide with 2-chloro-pyridine and trifluoromethanesulfonic anhydride ^[3]:

• Overview at chem.qmul.ac.uk

v • d • e Metabolism map

Glucuronate metabolism Pentose interconversion Inositol metabolism Cellulose and sucrose metabolism Starch and glycogen metabolism Other sugar metabolism Pentose phosphate pathway Glycolysis and Gluconeogenesis Amino sugars metabolism Small amino acid synthesis Branched amino acid synthesis Purine biosynthesis Histidine metabolism Aromatic amino acid synthesis Pyruvate decarboxylation Anaerobic respiration Fatty acid metabolism Urea cycle Aspartate amino acid group synthesis Porphyrins and corrinoids metabolism Citric acid cycle Glutamate amino acid group synthesis Pyrimidine biosynthesis  v • d • e  All pathway labels on this image are links, simply click to access the article. A high resolution labeled version of this image is available here.