Pyrimidine metabolism

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 first three enzymes are all coded by the same gene (CAD).

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.