Describing DNA

18th February 2005 at 00:00
They called it the key to life, and in the early 1950s, chemists the world over were hellbent on claiming it for their own. But the DNA molecule, whose complex structure carried the genetic codes for every living cell, would not give up its secrets easily. Frontrunner in the race was the California Institute of Technology's celebrated chemist Linus Pauling. His work on chemical bonding had revealed the structure of proteins, a breakthrough which won him a Nobel Prize for Chemistry in 1954.

For Cambridge chemists James Watson and Francis Crick, Pauling was both a threat and an inspiration. As Watson later wrote, they had to "imitate Linus Pauling and beat him at his own game". The difficulty lay in the size of their quarry. For although DNA was a giant among molecules, it was only observable with X-rays, being shorter than the wavelength of visible light. And who could possibly know how a helical molecule might diffract X-rays, and how to interpret the cryptic patterns that resulted?

Following Pauling's example, Watson began building models. And it was one such model, unsupported by experimental evidence, that led to the pair being taken off the DNA case.

Then, in January 1953, word reached them that Pauling had apparently solved the riddle. It was with a mixture of relief and disbelief, therefore, that the pair worked through Pauling's paper. For they saw almost at once that the great man had made an elementary blunder, and that his suggested structure was impossible.

"If a student had made a similar mistake," Watson wrote, "he would be thought unfit to benefit from CalTech's chemistry faculty." Having checked their reasoning in a copy of Pauling's own textbook, they drank "a toast to the Pauling failure" and got back to work.

On February 28, 1953, Watson and Crick revealed the double helix structure of DNA and, nine years later, received a Nobel Prize for their efforts. But if Pauling was still kicking himself, he did not show it. For in the same ceremony, he received his second Nobel Prize, for his longstanding opposition to nuclear bomb tests.

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