De Novo Synthesis pathway is used to produce nucleotides. The pathway completes in the liver of humans. The pyrimidine formation initiates with the formation of carbamoyl phosphate that includes a series of steps. In the first step, a biochemical reaction results in the formation of carbamoyl phosphate that involves bicarbonate, glutamine, ATP, and a water molecule.

The reaction is catalyzed by the enzyme carbamoyl aspartate transcarbamylase. Then, by intramolecular condensation, the ring closes and converts carbamoyl phosphate into dihydroorotate in presence of the enzyme dihydroorotase.

Later, the dihydroorotate is converted into orotate by dihydroorotate dehydrogenase. After the formation of the pyrimidine ring, 5-phospho-α-D-ribosyl-1-pyrophosphate (PRPP) reacts to orotate and form orotidine-5-monophosphate (OMP).

In the presence of the enzyme OMP decarboxylase, the OMP is decarboxylated and yield uridine monophosphate (UMP). Eventually, the dephosphorylation of ATPs and kinases produce UDP and UTP be a biosynthetic pathway. The purines are derived from nucleotide inosine monophosphate (IMP).

Amino acids glycine, glutamine, and aspartic acids are involved in the production of IMP from a pre-existing ribose phosphate. Then, the ribose5- phosphate reacts with ATP to form 5- phosphoribosyl-1-pyrophosphate (PRPP). PRPP is involved in both purine and pyrimidine synthesis as well as in NAD and NADP formation. Later, the IMP molecule is converted into adenosine monophosphate or guanosine monophosphate (GMP).