Apart from occurring in nucleic acids, pyrimidines are also found in

Usually, purine and pyrimidine are found in nucleic acids (DNA and RNA) as a part of nucleotides. Pyrimidines also occur in thiamine (vitamin B1) and alloxan. Purine is also a structural component of a number of essential coenzymes, e.g. coenzyme-A, NAD+, NADP+ and FAD+.