A partial list of trivial names of various pyrimidines exists. Folate derivatives participate in the biosynthesis of both purines and pyrimidines. De novo synthesis of pyrimidines and purines follows two different pathways. Nucleotides can be separated into purines and pyrimidines. The complementary nitrogenous bases are divided into two groups, pyrimidines and purines. These bases are heterocyclic rings containing nitrogen, classified as purines or pyrimidines. In DNA, these bases form hydrogen bonds with their complementary pyrimidines, thymine and cytosine, respectively. Nucleotides may be divided into two categories&colon; purines and pyrimidines. Amination and hydroxylation has been observed for substituted pyrimidines. The bases in the DNA are classified as purines and pyrimidines. Several modifications, such as 2'-fluorine-substituted pyrimidines, polyethylene glycol (PEG) linkage, etc. The nucleobases are divided into purines (guanine and adenine) and pyrimidines (cytosine, thymine and uracil). The total amount of pyrimidines is equal to the total amount of purines. Pyrimidines are ultimately catabolized (degraded) to CO, HO, and urea. Adenine and guanine are purines, cytosine and uracil are pyrimidines.