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Bought a standard poodle puppy.  Bringing him home October 5, so October will be full of housebreaking, and FUN.

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Tuesday
Nov232010

Photograph 51: Rosalind Franklin and the DNA Double Helix, Part 3

In my last two posts I introduced the history of Rosalind Franklin’s revelation of the molecular structure of DNA.

         Once Franklin saw that her colleague and nemesis Maurice Wilkins had two different forms of DNA mixed together in his sample, she figured out a way to produce pure forms of both DNA crystal types, the A form (dehydrated) and the B form (hydrated).  Then she set about getting X-ray photos of each crystal type.

         After less than two years, by the beginning of 1953, Franklin not only had produced superb X-ray photos of both forms, she had figured out roughly the helical structure of DNA, and had become fairly certain the molecule was not single or triple, but double. 

         She knew that the phosphate-sugar backbones of the two DNA strands were on the outside of the molecule, and that the 4 bases, adenine (A), thymine (T), guanine (G), and cytosine (C), were tucked inside.  She knew the dimensions of both forms.  And she was just beginning to suspect how the molecule might work to allow inheritance of genes.

         It was at this point that Wilkins handed over a copy of Franklin’s Photograph 51, a superb X-ray photo of the B form, to James Watson and Francis Crick.  The latter two also got their hands on a report Franklin had written about the crystal form and dimensions. 

         Combining the photo and the report, Crick and Watson built a model of the DNA double helix, with single chains running in opposite directions.  But the model didn’t fit together well. 

         Jerry Donohue, another fellow scientist, pointed out to Watson that he was modeling with the wrong forms of the bases.  Once Watson corrected that problem, he found that his DNA model fit together perfectly to match Rosalind Franklin’s photograph.

         Although the women’s movement later deplored Franklin’s not being credited at the time, Franklin seems not to have cared.  She went on to do excellent and important work with tobacco mosaic and polio viruses at Birkbeck College, London.

         The Crick/Watson model was not altogether correct and was not accepted immediately.  Franklin, alas, died prematurely at 37 of ovarian cancer, so the Nobel Prize she should have shared was awarded some time after her death.

         But what a wonderful scientist and person she was.  I highly recommend the Brenda Maddox book pictured above.

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