Guanine suna ne da ke nufin wani fili na crystalline wanda yake ɗaya daga cikin manyan tushe guda huɗu na nucleotide da ke cikin DNA da RNA. Ana wakilta ta da harafin "G" a cikin lambar kwayoyin halitta da kuma nau'i-nau'i tare da cytosine a cikin DNA kuma tare da cytosine ko uracil a cikin RNA. Guanine kuma wani bangare ne na kwayoyin canja wurin makamashi ATP (adenosine triphosphate) da na coenzyme NADH (nicotinamide adenine dinucleotide). Tsarin sinadarai na guanine shine C5H5N5O.