Guanine is one of the four main building blocks of DNA and RNA, the molecules that carry genetic information in living organisms. It is classified as a purine, which is a type of nitrogenous base. In DNA, guanine pairs with cytosine through hydrogen bonds, helping to stabilize the structure of the double helix. In addition to its role in genetics, guanine is also involved in various biochemical processes. It is a component of GTP (guanosine triphosphate), which serves as an energy source for cellular activities. Guanine can also be found in certain coenzymes and plays a role in signaling pathways within cells.