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In 1962, James Watson, Francis Crick, and Maurice Wilkins shared the Nobel Prize for Medicine or Physiology for discovering the structure of DNA (deoxyribonucleic acid), the molecule that contains all of the information necessary to create and maintain a living organism. The accepted narrative of how this came about is that Watson & Crick were hard at work on trying to determine the structure of DNA (competing with Linus Pauling), while Wilkins provided them with a crucial piece of evidence, an x-ray photograph of DNA taken by Rosalind Franklin (Photograph 51, pictured above); the photograph was shared without her knowledge. According to Watson’s account in his memoir The Double Helix, upon seeing the photograph, he immediately understood that DNA had a helical structure, and with Crick, was able to determine the detailed structure of this crucial biological molecule. The implication was that Franklin was unable to understand the significance of her own x-ray data. Because she died of ovarian cancer in 1958, at the age of 37, she was not eligible to share in the Nobel Prize. This narrative simultaneously reveres Franklin (for obtaining the crucial piece of data) while chiding her (for missing its significance).
In a new account published in Nature, two science historians have obtained access to archival materials that revise this narrative.
At that time, DNA had been purified in two different forms; Franklin had designated these two forms as A and B. Form A was a crystalline form, while form B was wet, with a gelatinous consistency. X-ray images from crystalline solids give very sharp images which, when painstakingly analyzed, give precise relative locations for all the atoms present in the structure, while less well-ordered materials (such as form B DNA) give blurry images that, at best, only provide a few broad clues about the material’s structure. Not surprisingly, Franklin decided to first concentrate her efforts on attempting to interpret the crystalline form A, given its promise for the most precise data with regard to the molecule’s structure. To the extent that she made an error, it was to forget that in its natural environment, DNA is wet, which implies the B form structure would be more pertinent to what functioning DNA looks like.
Watson’s claim to having an epiphany on seeing Photograph 51 are specious, for two reasons. First, Franklin was an expert at x-ray diffractometry, and hence would be able to recognize overall patterns right away. Watson, on the other hand, had never done any x-ray work and knew little or nothing about the interpretation of diffraction patterns. It is highly unlikely that he woud have been able to see something in the data that she hadn’t already seen for herself. Second, by the time that Watson saw Photograph 51, it was well known among researchers already that DNA was a helical molecule. The “Eureka” moment that Watson wrote in his memoir is provided for dramatic effect and little else. Further, given that Photograph 51 has attained mythical status among some historian of science, recognition of these facts kind of deflates that significance.
The science historians who wrote the Nature article (Matthew Cobb and Nathaniel Comfort), however, determined Franklin’s true role in helping Watson & Crick to figure out DNA’s structure from perviously unknown archival documents, in particular a draft article for Time magazine that was never published, and an informal progress report (never published) written by the group at King’s College London (where Franklin was at the time) to which Franklin contributed the crucial piece of information that the helix of the B form repeated every 34 Angstroms, and that the repeat contained approximately 10 units.
In her contribution to the MRC report, Franklin had confirmed the 34 Å result for the B form. She also reported that the unit cell (the repeating unit of the crystal) of DNA was huge; it contained a larger number of atoms than any other unit cell in any other known molecular structure. Franklin also added some key crystallographic data for the A form, indicating that it had a ‘C2’ symmetry, which in turn implied that the molecule had an even number of sugar-phosphate strands running in opposite directions.
Notes by Crick for a lecture on the history of the double helix, given to historians of science at the University of Oxford in May 1961, together with formal and informal remarks made throughout his life, reveal that, unlike Photograph 51, this report was truly significant for confirming the structure that Watson and Crick eventually obtained.
...
Franklin’s data and Watson and Crick’s many conversations with Wilkins had provided what seem like key pieces of information — the phosphate groups were on the outside of the molecule; there was a repeat every 34 Å; perhaps there were ten bases per repeat and an even number of strands running in opposite directions (the implication of the C2 symmetry). Yet, according to their own accounts, the pair ignored every one of these facts at one point or another during those six weeks. Once they had hit on a conceptual model of the structure, the MRC report provided a valuable check on their assumptions.
Franklin also grasped, independently, one of the fundamental insights of the structure: how, in principle, DNA could specify proteins. In February 1953, she was working hard to finish her analyses of DNA before leaving King’s. The A form had continued to resist her attempts to interpret it, so she had turned to the much simpler, clearly helical B form. Her notes reveal that by late February, she had accepted that the A form was also probably helical, with two strands, and she had realized that the order of the bases on a given strand had no effect on the overall structure. This meant that any sequence of bases was possible. As she noted, “an infinite variety of nucleotide sequences would be possible to explain the biological specificity of DNA”14. This idea, which Watson and Crick grasped at around the same time, had first been proposed in 1947 by chemist John Masson Gulland at University College Nottingham, UK (now the University of Nottingham)15.
Rosalind Franklin understood what she was doing, and she kept abreast of the developments through informal communications. She was hobbled in her efforts because she was working alone and had no one on-site to be able to trade ideas with. It would be nice if the standard narrative were corrected in the popular account in peoples’ minds, but given how ubiquitous The Double Helix is (I, too, have a copy), that’s going to be tough to do.
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