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|Section2= |Section7= |Section8= }} Guanine (G, Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with conjugated double bonds. Being unsaturated, the bicyclic molecule is planar. The guanine nucleoside is called guanosine. ==Basic principles== Guanine, along with adenine and cytosine, is present in both DNA and RNA, whereas thymine is usually seen only in DNA, and uracil only in RNA. Guanine has two tautomeric forms, the major keto form (see figures) and rare enol form. It binds to cytosine through three hydrogen bonds. In cytosine, the amino group acts as the hydrogen bond donor and the C-2 carbonyl and the N-3 amine as the hydrogen-bond acceptors. Guanine has the C-6 carbonyl group that acts as the hydrogen bond acceptor, while a group at N-1 and the amino group at C-2 act as the hydrogen bond donors. The first isolation of guanine was reported in 1844 from the excreta of sea birds, known as guano, which was used as a source of fertilizer; guanine was named in 1846.〔Guanine was first isolated by Prof. Magnus' student, B. Unger in 1844. See: * Paul O. P. Ts'o, ''Basic Principles in Nucleic Acid Chemistry'', vol. 1 (New York, New York: Academic Press, 1974), (page 7. ) * Magnus (1844) ("Ueber das Vorkommen von Xanthicoxyd im Guano" ) (On the occurrence of xanthic oxide in guano), ''Annalen der Chemie und Pharmacie'', 51 : 395-397. * B. Unger (1846) ("Bemerkungen zu obiger Notiz" ) (Comments on the above notice), ''Annalen der Chemie und Pharmacie'', 58 : 18-20. From page 20: ''" … desshalb möchte ich den Namen ''Guanin'' vorschlagen, welcher an seine Herkunft erinnert."'' ( … therefore I would like to suggest the name ''guanine'', which is reminiscent of its origin.) * B. Unger (1846) ("Das Guanin und seine Verbindungen" ) (Guanine and its compounds), ''Annalen der Chemie und Pharmacie'', 59 : 58-68.〕 Between 1882 and 1906, Fischer determined the structure and also showed that uric acid can be converted to guanine. Guanine can be hydrolyzed with strong acid to glycine, ammonia, carbon dioxide, and carbon monoxide. Guanine is first deaminated to xanthine. Guanine oxidizes more readily than adenine, the other purine-derivative base in DNA. Its high melting point of 350 °C reflects the intermolecular hydrogen bonding between the oxo and amino groups in the molecules in the crystal. Because of this intermolecular bonding, guanine is relatively insoluble in water, but it is soluble in dilute acids and bases. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Guanine」の詳細全文を読む スポンサード リンク
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