guanine

A nitrogenous base, more correctly described as 2-amino-6-oxypurine, derived from amino acids and sugars and found in all living organisms. Guanine combines with pentose sugar phosphates to form one of the nucleotides making up *RNA and *DNA . In addition, hydrolysis of the *nucleoside guanosine triphosphate (*GTP) releases energy to drive some energetically unfavourable reactions. See also nucleotide.