Nucleic acids contain sugars, phosphoric acid, purines and pyrimidine bases. The two most studied nucleic acids are chemicals found in the genes: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA is the chemical basis of heredity (and genetic diseases) and is organized into genes, the fundamental units of genetic information. Genes control the synthesis of various types of RNA, most of which are involved in protein synthesis. In other words, DNA directs the synthesis of RNA, which in turn directs protein synthesis.
DNA is made up of four bases, adenine, guanine, cytosine and thymidine, which can be found in both purine and pyrimidine deoxyribonucleotide forms. (There is a fifth nucleic acid, inosine, but it is not part of this pairing system.) Adenine molecules pair up with thymidine, and cytosine with guanine to form the well-known double strand, or double helix, DNA model. Genetic "messages" are transferred because of the actions of the purine and pyrimidine bases. These messages form encoded genetic instructions that guide the development of all living cells. RNA, on the other hand, exists in several different single-stranded structures, most of which are involved in protein synthesis.
Although humans ingest dietary nucleic acids and nucleotides through both plants and meats, survival does not require the absorption and utilization of the nucleotides. Humans can synthesize ample amounts of purine and pyrimidine nucleotides at sufficient rates. Dietary nucleic acids are eventually broken down in the gastrointestinal tract into purines and pyrimidines, but they are not incorporated into tissue nucleic acids. However, injected purine or pyrimidine analogs, including potential anti-cancer drugs, may be incorporated into DNA. Diseases involving abnormalities in purine metabolism include gout, Lesch-Nyhan syndrome, adenosine deaminase deficiency, and purine nucleoside phosphorylase deficiency. Diseases of pyrimidine biosynthesis are more rare because the products of pyrimidine catabolismÑcarbon dioxide, ammonia and beta-aminoisobutyrateÑare highly soluble.
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