Differences in Purines & Pyrimidines

Purines and pyrimidines have many features in common. Both are organic, nitrogen-containing compounds that are widely distributed in nature; each serves a vital purpose in the function and replication of biological systems. Both purines and pyrimidines are classified as heterocyclic aromatic compounds, which results in similar chemical behaviors. Despite these similarities, the differences in structure and function of these crucial compounds make life possible. For instance, the differences in these two types of molecules allow for DNA to exist as a double stranded structure. The ability of living organisms to replicate their genetic data, which lies in the specific sequence of purines and pyrimidines, is the basis of evolution and all of modern biology.

Structure

• Purines have a molecular structure containing a six-membered ring bound to a five-membered ring, both of which contain nitrogen atoms. The molecular structure of pyrimidines is simpler, containing only a single, six-membered ring.

Purine Function

• Several forms of purines are common in nature. Representing approximately half of your genetic code, purine molecules are contained within adenine and guanine, two compounds known as nucleotide bases. Commonly abbreviated "A" and "G," these two nucleotides are the building blocks of DNA and are critical to the process of information storage and replication. Other examples of purines include uric acid and caffeine.

Pyrimidine Function

• The other half of your genetic code is spelled out with pyrimidines. Cytosine and thymine, also known as "C" and "T," are pyrimidines within your DNA sequence. Another abundant pyrimidine in nature is known as uracil. This molecule is present only within a specific nucleic acid, known as RNA. When combined in sequence with A, G, and C, uracil is a building block of RNA molecules, which are critical to cell function and replication.

Uses in Metabolism and Neurotransmission

• Purines carry out several functions important to cellular metabolism. Vital to the production and storage of energy within the cell, purines are contained within the biochemical structure of molecules such as ATP, GTP, cAMP, NADH, and coenzyme A. Purines also function as chemical neurotransmitters; adenosine, for instance, can transmit information to cells by binding to receptors on membrane surfaces.

Role in Disease

• Purines have been linked to gout, an extremely painful joint condition. This type of arthritis occurs when elevated blood uric acid levels develop. This commonly occurring purine then accumulates within the joint, leading to severe swelling, inflammation, and pain.