Franklin's X-Ray Crystallography Experiments

    Regular substances like crystals diffract X-rays in characteristic patterns according to their physical structure. The X-ray photograph 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.

    Rosalind Franklin (1920-1958), who 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 she interpreted her evidence in the context of the biological problem of gene structure. Wilkins showed the photograph 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 picture of Franklin, which 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 ©  2011 by Steven M. Carr