Thursday, September 30, 2010

Further details of the DNA story revealed by Crick's lost correspondence

In the September 30 issue of Nature (Vol. 467, pp519-524), there is an interesting account of "The lost correspondence of Francis Crick" by Gann & Witkowski. The newly found letters, mostly between Crick and Wilkins, unveil further background information on the exciting DNA story. As the authors put it, "Strained relationships and vivid personalities leap off the pages."

I read Watson's "The Double Helix" book a while ago, and overall I am quite familiar with the DNA story. Still, I found this account fascinating: it provides a "CAST LIST" in "The search for the structure of DNA" with photos (p521); and it succinctly summarizes the relationships among the key players. In science, no other story shows more dramatically the collaborative and competitive nature among scientists working on similar projects.

Franklin’s X-ray diffraction photograph 51 of B-form DNA (see figure above, from Wikipedia), with its unambiguous evidence that DNA was helical, proved crucial for Watson and Crick to determine the structure of DNA. Indeed, the Watson-Crick DNA model corresponds to the B-form DNA, with its base-pairs in the middle, parallel to each other and perpendicular to the linear helical axis.

From this Nature account, however, I noticed for the first time a subtle detail: when B-form DNA photograph 51 was shown to Watson by Wilkins in early 1953, Franklin also already had the A-form DNA diffraction pattern. According to the authors,

It was the A-structure diffraction pattern that had led Franklin away from believing that DNA, in that form at least, was helical, despite her already having produced the most persuasive helical pictures of the B structure — including photograph 51. The crystalline DNA gave better quality diffraction data, more suited to her painstaking, quantita- tive approach, and so she focused on the A form during 1952. It was at this time that she and Gosling made a handwritten, black edged funeral card announcing the death of “DNA Helix(crystalline)”.

When Crick had the opportunity to look the A-form DNA diffraction picture, on 5 June 1953, he wrote (to Wilkins):
This is the first time I have had an opportunity for a detailed study of the picture of Structure A, and I must say I am glad I didn’t see it earlier, as it would have worried me considerably.

I am reading "Blink: The Power of Thinking Without Thinking", a book by Malcolm Gladwell. The above case serves as a vivid example.