Guanine is one of the four main building blocks of DNA and RNA, which are essential molecules for life. It is a type of nitrogenous base, specifically classified as a purine. In DNA, guanine pairs with cytosine to help form the structure of the double helix, while in RNA, it plays a similar role. Guanine is not only important for genetic information but also plays a role in cellular processes. It is involved in the formation of GTP (guanosine triphosphate), a molecule that provides energy for various cellular functions. Overall, guanine is crucial for both heredity and energy transfer in living organisms.