A purine is a complex organic compound that forms the basis of all genetic material and a number of other biochemically significant components. Its chemical structure is composed of a pair of five- and six-member nitrogen-containing rings fused together. However, purines are not found in nature. Instead, they are synthesized organically by living organisms.
Sources
Purines are found in organ meat, game meat, seafood, dairy, gravy, dried beans, peas, the yeast of beer and wine. The liver, a delicacy in many cultures, is the largest source because it's the main site of purine metabolism. However, plant-based foods are generally lower in purines. The body can synthesis all the purine it needs both from dietary purines and from simpler molecules independent of purine intake.
Genetic Material
The largest task of purines is in the synthesis of nucleotides such as DNA and RNA. Nucleotides are in the shape of a double helix. Molecules called base pairs connect the helixes together like the rungs of a ladder. It is these base pairs that code the genetic information. Two of the four base pairs --- adenine and guanine --- are officially classified as purines. In DNA, adenine always bonds with thymine, and guanine always bonds with cytosine, so the two purines never connect with each other. The purpose of the base pairs within DNA is to "transcribe" the precise sequence of amino acids within a protein molecule.
Energy Transfer
Purines have one other critical function. They form the basis of an important class of molecules such as ATP and GTP that transfer energy between different parts of your body. For example, your cells create ATP through the process of cellular respiration in order to fuel various reactions such as muscle contractions. When the bonds of these molecules are broken, they release energy.
Warning
The liver breaks down any unneeded purines into a waste product known as uric acid. Though uric acid is relatively benign on its own --- and in many cases it can actually protect the blood from damage --- high levels can cause the buildup of needle-like crystals in the joints, especially in the joint at the base of the big toe. This is an inflammatory condition known as gout. A 2004 study published in "The New England Journal of Medicine" found that higher levels of meat and seafood consumption by men are associated with an increased risk of gout. However, purine-rich vegetables did not increase the risk of gout, and the consumption of dairy actually decreased it.
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