In the mid-to-late 1940s, scientists began to suspect that the molecules that are responsible for heredity were not proteins, but in fact DNA, short for deoxyribonucleic acid. But how could a molecule long considered to be simple and inert hold the secret of life? The Nobel Prize in Physiology or Medicine in 1962 was awarded to James Watson, Francis Crick and Maurice Wilkins for their discovery of the molecular structure of DNA, which helped solve one of the most important of all biological riddles.

Wilkins and his colleague Rosalind Franklin provided the key X-ray diffraction patterns that Watson and Crick used, as well as information from many other scientists, to build the definitive model of DNA’s structure. The structure, as simple and elegant as it is profound, shows that two long strands of DNA run in opposite directions and spiral around one another in the shape of a double helix. Another vital element in the structure is that four organic bases – known as adenine, thymine, cytosine and guanine – are paired in a specific manner between the two helices in such a way as to provide a natural scaffold for the two strands.

Watson and Crick’s structure of DNA could also explain how information is transferred in living material. The specific base pairing facilitates the perfect copying facility for heredity, while the specific order of bases forms the blueprint for the sequence of amino acids in a protein. DNA molecules can ‘unzip’ into two separate strands, and when the cell’s machinery creates matching strands, the specific pairing between the bases ensures that you get two faithful copies where you had one before. Watson and Crick’s paper revealing the structure, published in Nature on 25 April 1953, contains perhaps one of scientific literature’s most famous understatements: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”