Nucleotides are the building blocks of the DNA and RNA molecules that make up genes. While there are several types of nucleotides in genes, we are going to represent all of them in Petri Dish with a single generic nucleotide, orotidine 5'-monophosphate (OMP). OMP is a precursor for building other nucleotides, such as cytosine, uracil, and thymine. And phosphoribosyl pyrophosphate (PRPP), an intermediate in the building of OMP in our metabolic pathway, is a precursor for building adenine and guanine.

Nucleotide synthesis begins by diverting glucose-6-phosphate and oxaloacetate from the cellular respiration pathway and glutamate from the amino acid synthesis pathway. Glucose-6-phosphate is used to build phosphoribosyl pyrophosphate (PRPP) in step 1, and oxaloacetate and glutamate are used to build aspartate in step 2, which is then used to build orotate in step 3. Phosphoribosyl pyrophosphate and orotate are then combined to form our generic nucleotide in step 4.

The metabolic pathway for building orotidine 5'-monophosphate in Petri Dish has been simplified. Here is a more detailed version of the actual pathway: