| RTECS = MF8260000 }} | Section2 = | Section7 = | Section8 = }} Guanine's one of the five main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, thymine, and uracil. In DNA, guanine's paired with cytosine. With the formula C5H5N5O, guanine's a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with conjugated double bonds. Being unsaturated, the bicyclic molecule's planar. The guanine nucleoside's called guanosine. Basic principle… (More on Guanine)