© Science Museum/Science and Society Picture Library
DNA determines the genetic inheritance of every living organism. The discovery of its structure helped to resolve one of the central problems in biology. For many years it had been known that the cell must contain some kind of 'genetic blueprint', but the way in which this might operate was not clear until Crick and Watson devised this model in 1953.
By the 1950s many scientists believed that DNA (Deoxyribo Nucleic Acid) must be the substance which carries the genetic information. The challenge was to discover its structure. This structure had to explain two essential questions: how the material was copied so faithfully when cells divided, and how it could carry a code to build the 'machinery' and structure of the cell - the enzymes and other molecules.
The inspirational part of Crick and Watson's work was to conceive a double-helix structure, like a twisted ladder, which explained both the known chemical data and the X-ray analysis coming from Rosalind Franklin and Maurice Wilkins at King's College, London.
This structure showed how the molecule could divide at cell division and ensure the production of two identical copies. It also suggested how the 'rungs' of the ladder, made of pairs of chemical bases (adenine, thymine, guanine and cytosine) might carry a 'message' in a linear code.
The idea seized the imagination of researchers around the world and by 1961 the main elements of the code, by which DNA orders the assembly of amino acids and determines the types of proteins that are made, had been made investigated and understood.