 a purine is a heterocyclic aromatic organic compound. it consists of a pyrimidine ring fused to an imidazole ring. purines, which include substituted purines and their tautomers, are the most widely occurring nitrogen-containing heterocycle in nature.rosemeyer, h. chemistry & biodiversity 2004, 1, 361. purines and pyrimidines make up the two groups of nitrogenous bases, including the two groups of nucleotide bases. two of the four deoxyribonucleotides and two of the four ribonucleotides, the respective building-blocks of dna and rna, are purines. ==notable purines== there are many naturally occurring purines. two of the five bases in nucleic acids, adenine (2) and guanine (3), are purines. in dna, these bases form hydrogen bonds with their complementary pyrimidines thymine and cytosine, respectively. this is called complementary base pairing. in rna, the complement of adenine is uracil instead of thymine. other notable purines are hypoxanthine (4), xanthine (5), theobromine (6), caffeine (7), uric acid (8) and isoguanine (9). 550px ==functions==  aside from the crucial roles of purines (adenine and guanine) in dna and rna, purines are also significant components in a number of other important biomolecules, such as atp, [[guanos
Purines