The primary function of DNA in cells is to store and transmit genetic information. DNA contains the instructions necessary for the development, functioning, growth, and reproduction of all known living organisms. It encodes the information to build proteins, which perform most life functions. During the processes of replication and transcription, DNA is copied and converted into RNA, which then guides protein synthesis. This central role of DNA underpins the biological unity and diversity of life, as it dictates heredity and evolution.