 Purines and pyrimidines make up the two groups of nitrogenous bases, including the two groups of nucleotide bases.Two of the four deoxyribonucleotides (deoxyadenosine and deoxyguanosine) and two of the four ribonucleotides (adenosine, or AMP, and guanosine, or GMP), the respective building blocks of DNA and RNA, are purines.In order to form DNA and RNA, both purines and pyrimidines are needed by the cell in approximately equal quantities.