Deoxyribonucleic Acid (DNA) is a double-stranded, helical molecule. It consists of two sugar-phosphate backbones on the outside, held together by hydrogen bonds between pairs of nitrogenous bases on the inside. The bases are of four types (A, C, G, & T): pairing always occurs between A & T, and C & G. James Watson (1928 – ) and Francis Crick (1916 – 2004) realized that these pairing rules meant that either strand contained all the information necessary to make a new copy of the entire molecule, and that the aperiodic order of bases might provide a “genetic code”.

    Watson and Crick shared the Nobel Prize in 1962 for their discovery, along with Maurice Wilkins (1916 – 2004), who had continued research to provide a large body of crystallographic data supporting the model. Working in the same lab, Rosalind Franklin (1920 – 1958) had earlier produced the first clear crystallographic evidence for a helical structure. Crick went on to do fundamental work in molecular biology and neurobiology. Watson become Director of the Cold Spring Harbor Laboratory, and headed up the Human Genome Project in the 1990s.