Purines and pyrimidines are substances that perform several important functions in the body. Serving as a form of energy for the cells, they are essential for the production of DNA and RNA, production of proteins and starch, regulation of enzymes, and for cell signaling. Abnormalities in purines and pyrimidines can lead to various disorders.
Definitions
Purines and pyrimidines are called heterocyclic compounds, because they are made out of different kinds of atoms in the shape of a ring, as explained in "Harper's Illustrated Biochemistry" by Victor Rodwell, Ph.D., Emeritus Professor of Biochemistry at Purdue University. If the purines or pyrimidines have a sugar attached to them, they are called nucleosides. Deoxyribonucleosides have a sugar attached to a purine or pyrimidine and form part of DNA. Ribonucleosides have an attached sugar and make up RNA.
Forms of Purines and Pyrimidines
The main purines and pyrimidines make up DNA and RNA. Adenine and guanine are the purines of both DNA and RNA. Cytosine and thymine are the pyrimidines of DNA, while cytosine and uracil are the pyrimidines of RNA. According to Dr. Rodwell, 5-methylcytosine and 5-hydroxymethylcytosine are other purines and pyrimidines that form part of RNA and DNA. Other forms include xanthine, hypoxanthine and uric acid, which form from the breakdown of guanine and adenine.
Functions
Besides being part of the structure of RNA and DNA, purines and pyrimidines have other important functions. They are part of adenosine 5'-triphosphate, or ATP, which is the main form the cells use for energy. They help send signals, make proteins and regulate the activities of enzymes. Enzymes are proteins used by the cells to speed up the amount of time a reaction will take. Purines and pyrimidines also attach to vitamins, lipids and sugars, writes Dr. Rodwell. They even help make starch and glycogen--or the storage form of glucose.
Disorders
Problems with the metabolism of purines and pyrimidines can lead to several disorders, as described in "The Merck Manual for Healthcare Professionals" by Chin-To Fong, M.D., chief of the Division of Pediatric Genetics at the University of Rochester School of Medicine and Dentistry. In the case of an adenosine deaminase deficiency, people do not have enough of the adenosine deaminase enzyme, which leads to the accumulation of adenosine and interferes with the duplication of DNA. Lesch-Nyhan syndrome results from problems metabolizing guanine and hypoxanthine, which can cause gout. People with xanthine oxidase deficiency do not have a sufficient amount of the xanthine oxidase enzyme, and they accumulate xanthine.
Problematic Symptoms
In the case of an adenosine deaminase deficiency, the problem with duplicating DNA especially affects the immune cells, explains Dr. Fong. The immune cells help fight against foreign substances. Without them, people with this disorder have skeletal abnormalities, diarrhea and reoccurring infections. People with Lesch-Nyhan syndrome have gout, but are also very compulsive and aggressive. They often mutilate themselves, can be mentally retarded and make abnormal muscle movements. In individuals with a xanthine oxidase deficiency, people may have urinary tract infections and blood in their urine.
References
- "Harper's Illustrated Biochemistry"; Robert Murray, M.D., Ph.D., David Bender, Ph.D., Kathleen Botham, Ph.D. et al.; 2009
- The Merck Manual for Healthcare Professionals: Purine and Pyrimidine Metabolism Disorders
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