Watson and Crick

Francis CrickWhen, in October 1951 James Watson joined the Cavendish Laboratory at Cambridge headed by WL Bragg, he began a lengthy and fruitful collaboration with Francis Crick.

Wilkins had written to Crick about the key structure of DNA and included a sketch of the helical structure. Watson also commented on this work to his mentor Max Delbruck.

In November, Watson attended a seminar by Rosalind Franklin but failed to remember key data about the water content of DNA. Watson and Crick got started by building a model of DNA as a triple helix with phosphate models on the inside.

When Wilkins and Franklin were invited to the Cavendish to see it Franklin pointed out that this solution was flawed because it had taken insufficient account of water absorption.

James WatsonMaurice Wilkins achieved a major breakthrough in January 1953 when he concluded that the bases in DNA had to be arranged in hydrogen bonded, planar pairs.

Crucially, Wilkins then shared Franklin's photograph taken on 2 May 1952 with Watson. Franklin was, in February 1953, also closing in on the structure, interpreting the B pattern as two chain helices.

Simultaneously, Watson learnt that he had been using the wrong chemical form of one of the key bases and this led to the realisation, on 28 February 1953 that the base pairs of the chemical molecules do not bond like to like but adenine to thymine and guanine to cytosine.

Crick agreed and the two-chain model fell into place.

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