Seventy years ago, on 25 April 1953, James Watson and Francis Crick published their proposed double helix structure for a molecule of deoxyribonucleic acid (DNA — see CHEMISTRY REVIEW Vol. 22, No. 4, 'Celebrating the double helix'). They had gathered evidence from several scientific papers and (as yet unpublished) diffraction patterns, which had been created during X-ray crystallographic investigations of DNA by Rosalind Franklin. Crick, Watson and Maurice Wilkins were awarded the 1962 Nobel prize in physiology or medicine ‘for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material’.
Scientists had known of the existence of nucleic acids in cell nuclei since the nineteenth century. Researchers determined the chemical composition of nucleic acids in terms of the nucleobases (or simply bases): adenine, cytosine, guanine, thymine and uracil (we now know that the latter is only found in RNA, not DNA). During the early twentieth century the building blocks of the nucleic acids were shown to be nucleotides, which consist of a phosphate, a sugar and a base. Initially, the nucleic acids were believed to be short molecules and it was not until 1952 that Alfred D. Hershey and Martha Chase demonstrated that DNA is the molecule responsible for inheritance (Hershey received the 1969 Nobel prize in physiology or medicine).
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