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DNA: the King's story

Alexander Stokes (1919-2003)

Alexander StokesAlexander StokesAlexander Stokes was born in Macclesfield in 1919 and attended school in Manchester, before moving to Trinity College, Cambridge, where he worked in the Cavendish Laboratories and completed a PhD in x-ray crystallography.

Stokes' particular expertise was in applying his remarkable mathematical skills to the results of crystallographic analysis. He was appointed a lecturer in physics at Royal Holloway College in 1945.

Stokes transferred his lectureship to King's in 1947 when he was recruited by John Randall to strengthen his pioneering biophysics group. In 1950, Stokes joined Maurice Wilkins' team studying the x-ray diffraction of the DNA molecule.

Wilkins and his group speculated that DNA might possess a helical structure and Stokes was assigned the task of mathematically predicting the appearance of an x-ray diffraction pattern of such a molecule.

Beevers-Lipson stripsBeevers-Lipson stripsStokes turned to a branch of mathematics known as Fourier analysis and armed with powerful calculating tools called Bessel functions, he described a helix-like structure that closely resembled the earliest X-pattern diffraction pictures that Wilkins and his colleagues had obtained from the analysis of strands of DNA.

Ironically, Stokes' wave-like Bessel functions, invented by a nineteenth-century astronomer and mathematician to simplify the measurement of star distances, were now being employed to help calculate the distances necessary for life: the macroscopic brought to the aid of the microscopic.

Stokes' calculations showed that the photographs were consistent with a helical structure, though they did not rule out alternatives: at this stage the precise configuration of any helical components and the macro-structure of the molecule was still ill defined.

Stokes remained at King's until his retirement in 1983, during which time he became chairman of the Board of Studies in Physics and undertook research on large biological molecules and on the light scattering by suspensions of randomly orientated long prisms and x-ray scattering of chain molecules.

He was responsible for a series of important articles and other publications including a well-regarded textbook entitled The principles of atomic and nuclear physics. Alexander Stokes died in February 2003.

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