Deoxyribonucleic acid (DNA) molecules consist of two long intertwined polymers of nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds, structured as the familiar double helix. DNA is responsible for the long-term storage of genetic information, and specifies the sequence of the amino acids within proteins. It is organized into structures called chromosomes, and contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The first accurate model of the structure of DNA was formulated by James Watson and Francis Crick in 1953. The genetic information from DNA is transmitted into the nucleus of cells by molecules of RNA, which controls certain chemical processes in the cell. Both DNA and RNA are considered essential building blocks of life.