Chemicals in the body under go many reactions. Sometimes they are broken apart; other times they are constructed, or changed into another molecule. This process can release or store energy. It can also be used to build new structures, such as cells or connective tissue. These biochemical processes are known as metabolism. Purine and pyrimidine are specific chemicals found in DNA and RNA and as energy carrying molecules. Disorders in their biochemical pathways, or metabolism, cause a number of diseases.
Functions of Purine and Pyrimidines
Genes are coded by long stretches of DNA. The two types of purines found in DNA are adenine and guanine, and the two types of pyrimidines are cytosine and thymine. DNA is copied by RNA, which tells the cell how to make proteins. RNA replaces thymine with uracil. In addition, some of these chemicals can be linked to phosphate to store and release energy for use by the cell.
Gout and Uric Acid
Purines are broken down into uric acid which is excreted through the kidneys into the urine and the intestines. Excessive uric acid results from the production of too much uric acid or a reduced ability to clear it from the body or both. Increased uric acid production can occur from the diet. Excessive red meat consumption is one trigger for gouty arthritis, a type of arthritis in which uric acid crystals precipitate in the joints. Some cancers, such as leukemia, the death of cancer cells from chemotherapy or normal cells from other causes can increase uric acid. Decreased elimination of uric acid is usually caused by kidney problems. In addition to gouty arthritis or gout, other complications from high uric acid include kidney disease and kidney stones.
Pyrimidine Metabolism Diseases
According to "Harrison's Principles of Internal Medicine" by Anthony S Fauci M.D. there are greater than 25 different enzymes involved in pyrimidine metabolism, and inherited disorders of these enzymes are rare, but seven pyrimidine metabolism disorders have been discovered such as dihydropyrimidine dehydrogenase or DPD, pyrimidine 5'-nucleotidase deficiency and orotic aciduria. The first of these causes neurological developmental delays and the latter two cause development delay along with blood problems.
Purine Disorders
Purine disorders are classified by problems with enzymes involved in reusing purines, known as purine salvage, problems breaking down purines and problems with building purines. HPRT deficiency, also known as Lesch-Nyhan syndrome is a problem with purine salvage. It causes high uric acid, muscle problems, self-mutilating behavior and developmental delay. An example disease causing problems with purine breakdown is the myoadenylate deaminase deficiency. This usually causes mild muscle aches with exercise. An example of a problem building purines is PRPP synthetase overactivity. This disease results in kidney stones, gout and sometimes deafness.
References
- "Lehninger Principles of Biochemistry"; David L. Nelson and Michael M. Cox; 4th Ed 2004
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci et al; 17th Ed 2008
Member Comments