noun, plural: purines
A heterocyclic aromatic compound with a chemical structure comprised of an imidazole ring fused to a pyrimidine ring, and makes up nucleic acids (e.g. DNA and RNA) and certain alkaloids (e.g. caffeine and theophylline)
Nucleic acids such as DNA and RNA molecules contain the genetic information important for all cellular functions and heredity. Each nucleic acid is comprised of a series of nucleotides. The nucleotide, in turn, is made up of phosphoric acid, sugar (5-carbon), and nitrogenous base. The nitrogenous base is a fundamental component of nucleotides and nucleosides and occurs in two major forms: purines and pyrimidines.
Purine is a heterocyclic organic compound. Its chemical structure is comprised of a pyrimidine ring with an imidazole ring fused to it, thus, has a total of four nitrogen atoms and two carbon rings. The pyrimidine ring contains two nitrogen atoms that are located at positions 1 and 3 of the ring (similar to those of pyrimidines). The imidazole ring attached to the pyrimidine ring has two nitrogen atoms that are located at positions 7 and 9.
In DNAs, purines complementary base pair with pyrimidines. In particular, guanine (a purine) pairs with cytosine (a pyrimidine) while adenine (another purine) pairs with thymine (another pyrimidine). In RNA, thymine is replaced by uracil and therefore adenine complementary pairs with uracil instead of thymine. The term purine bases refer to guanine and adenine whereas the pyrimidine bases pertain to the cytosine, thymine, and uracil.
Apart from nucleic acids, purines are also important components of certain proteins and starches. Thus, their functions are not just to serve as structural constituents of DNA and RNA but they are also involved in the regulation of enzymes and cell signaling. Examples of purines other than purine bases are hypoxanthine, xanthine, theobromine, caffeine, uric acid and isoguanine.
Uric acid is the metabolic end product of purine metabolism. In the diet, purines are found in high amounts in liver, kidney, and other internal organs. They are also present in meat, seafood, cauliflower, beans, mushrooms, etc. in moderate amounts.