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

De novo biosynthesis of pyrimidine

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

The synthesis of UMP.

The color scheme is as follows: enzymes, coenzymes, substrate names, inorganic molecules

The first three enzymes are all coded by the same gene in Metazoa (CAD). In Fungi, a similar protein exists but lacks the dihydroorotase function: another protein catalyzes the second step.

In other organisms (Bacteria, Archaea and the other Eukaryota), the first three steps are done by three different enzymes.

Pyrimidine catabolism

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}

Pharmacotherapy

Modulating the pyrimidine metabolism pharmacologically has therapeutical uses.

Pyrimidine synthesis inhibitors are used in active moderate to severe rheumatoid arthritis and psoriatic arthritis. Examples include Leflunomide.

External links

• Overview at Queen Mary, University of London

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.