Franklin's X-Ray Crystallography Experiments

    Regular substances like crystals diffract X-rays in characteristic patterns according to their physical structure. The X-ray crytallograph at right shows the diffraction pattern of a crystallized DNA molecule. The cross pattern in the middle is characteristic of a helical molecule with regular repeats; the broad bands at top and bottom give an indication of the periodicity of the repeats. The photograph is of the highly hydrated B form of DNA, rather than the A form, which does not show a distinct helical structure.

    Rosalind Franklin (1920-1958), whose grad student Raymond Gosling (1926 - ) made the photograph, worked as a post-doctoral researcher in the lab of Maurice Wilkins, and approached the structure of DNA as a physical problem in crystalline structure. Opinion and evidence vary as to how and when she interpreted her evidence as bearing on the helical nature of the molecule. Wilkins was given the photo by Gosling, and showed it to Watson, who immediately realized its implications. Watson, Crick, & Wilkins subsequently received the Nobel Prize in 1962 for solving the structure of DNA. By the time of the award, Franklin was dead: the Nobel is not awarded posthumously, nor to more than three persons. Watson's autobiographic account of the discovery of "The Double Helix" (1968) paints an unflattering personal portrait of Franklin, and was widely criticized as inaccurate and sexist. Anne Sayre's biography, "Rosalind Franklin and DNA" (1975) discusses the challenges faced by women in science. Watson and Crick repeatedly acknowledged that they could not have solved the structure without Franklin's evidence.

All text material ©  2014 by Steven M. Carr