On DNA's Anniversary: How Rosalind Franklin Missed the Helix

Less than a year before Watson and Cricks paper, A Structure for Deoxyribose Nucleic Acid, was published in Nature, 60 years ago today, Rosalind Franklin sent around a hand-lettered obituary:

Obituary for the helix. Wellcome Library.

Led astray by her own evidence, she had missed, just barely, making the greatest discovery in the history of biology: the coiled, interlaced structure that explained with such clarity the working of the gene. The secret of life, Crick called it.

Gosling, the other signatory, was Franklins assistant at Kings College in London, and Wilkins was her boss and bte noire. Besselised refers to Bessel functions, a mathematical tool used to analyze the photographic images she so expertly produced of DNA. But the most significant word in her mocking postcard was the one in parentheses: crystalline.

Several months earlier, having mastered better than anyone a technique called x-ray crystallography, she had taken the clearest pictures yet of the molecule. It came in two forms, depending on whether it was crystallized (shape A) or dissolved in water (shape B). It was the longer, stretched-out wet form, her Photo 51, that went on to become legendary. Horace Freeland Judson describes it in The Eighth Day of Creation:

The overall pattern was a huge blurry diamond. The top and bottom points of the diamond were capped by heavily exposed, dark arcs. From the bulls-eye, a striking arrangement of short, horizontal smears stepped out along the diagonals in the shape of an X or a maltese cross. The pattern shouted helix.

The question that has dogged historians ever since is why Franklin didnt shout out the same. Instead she put image B aside, concentrating instead on the far less certain pattern in image A. No matter how hard she looked, she couldnt see a helix there.

Franklins Photo 51. Wellcome Library.

She bristled when Crick, working with Watson at the Cavendish Laboratory in Cambridge, told her she was allowing herself to be misled by ambiguous markings and that both forms must be helical. But she couldnt be persuaded. Cautious by nature, she believed in holding back on interpretation and grand theories until all the data were gathered and understood, the seeming contradictions resolved. Her style was to work from the bottom up, meticulously trying to piece together the big picture.

She thought it was rash and premature that Crick and Watson, with their top-down approach, were enthusiastically building models castles in the air before they had laid the foundation. As they put together their sheet-metal and wire sculpture, the details, they believed, could be filled in along the way.

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On DNA's Anniversary: How Rosalind Franklin Missed the Helix