King's College London
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DNA: the King's story

X-ray diffraction and genetics

Sir William BraggSir William BraggShortly after the work of von Laue and Ewald in 1912, the crystallographers Walter Friedrich and Paul Knipping passed a beam of x-rays through a crystal of copper sulphate on to a photographic plate.

When the plate was developed, in addition to the dark spot produced by the undeflected beam, they also found an irregular pattern of black spots confirming the theory and encouraging the idea that the pattern of diffraction (the scattering of the spots) said something measurable about the molecular structure of the crystal.

Concerted work by a number of scientists including Sir William Bragg and John Desmond Bernal led both to the deduction of the molecular structure of a number of crystals and deduction of equations to interpret their use.

In March 1929 the Royal Institution established three committees on x-ray crystallography and organised the production and publication of 'International Tables for the Determination of Crystal Structures'.

When the technique of x-ray diffraction was used on protein molecules in the 1930s, the growing possibility of its use in exploring the secrets of genetics was recognised. Niels Bohr (of the Bohr atom) organised meetings on the subject.

Those attending included x-ray diffractionists Bernal and William Astbury, the geneticist Cyril Darlington, and John Turton Randall, a physicist.

Bernal and Dorothy Hodgkin in Cambridge pioneered the use of x-ray diffraction to study the crystals of protein molecules including the demonstration that successful photographs depended on keeping samples wet.

This realisation was to be crucial to the success of DNA experiments at King’s College London.

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