As a component of DNA and RNA, adenine, guanine, cytosine, thymine and uracil form the code which is used to assemble the proteins with the aid of the agents. Together with ribose or deoxyribose they form nucleosides, hence the names ribonucleic acid (RNA) or deoxyribonucleic acid (DNA).
Nucleic bases explained in Wikipedia (Wikipedia CC-by-sa-3.0)