DNA and RNA are made up of building blocks called bases. In DNA, there are four types of bases: adenine (A), thymine (T), cytosine (C), and guanine (G). These bases pair specifically, with A pairing with T and C pairing with G, forming the structure of the DNA double helix. In RNA, the base uracil (U) replaces thymine, so the four bases are A, U, C, and G. RNA plays a crucial role in translating the genetic information stored in DNA into proteins, which are essential for various functions in living organisms.