Linus Pauling and the Race for DNA: A Documentary History Narrative  
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Not Quite Over
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Crick and Watson were downcast by the news from Peter Pauling that his father appeared to have solved DNA.

Alternating between bouts of despair and denial - trying to figure out how he could have beaten them and then deciding that he certainly could not have without seeing Wilkins and Franklin's x-ray work and then thinking, well, of course, he is Pauling, so anything is possible - they continued working on the problem themselves. If they could come up with something independently before Pauling's paper appeared, at least they might share credit.

This time they added a critical observation. Crick and Watson knew Erwin Chargaff, an acerbic and opinionated Austrian-born biochemist who used chromatography to analyze the chemical composition of nucleic acids. Chargaff had told them about a simple relationship he had found between the occurrence of different bases in DNA: adenine and thymine were present in roughly the same amounts and so were guanine and cytosine. One of each pair was a larger purine; the other, a smaller pyrimidine.

Chargaff had told Pauling the same thing when they shared a shipboard dining room during an Atlantic crossing in 1947, but Pauling found Chargaff annoying and ignored his tip.

It made all the difference to Crick and Watson. Franklin's criticisms had already pointed them toward putting the phosphates on the outside of the molecule; now they had the clue of a one-to-one relationship between the bases on the inside. They began thinking about helixes in which the purines and pyrimidines lined up somehow down the core of the molecule.

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Audio Clip  Audio: The Most Important Example of Complementariness. January 17, 1983. (0:19) Transcript and More Information

Video Clip  Video: Chargaff's Rules. 1973. (0:54) Transcript and More Information

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Portrait of Erwin Chargaff. 1930.

Page 1
Letter from Peter Pauling to Linus, Ava Helen and Crellin Pauling. January 13, 1953.

"So far as I could make out, they wanted, unencumbered by any knowledge of the chemistry involved, to fit DNA into a helix. The main reason seemed to be Pauling's alpha-helix model of a protein....I told them all I knew. If they had heard before about the pairing rules, they concealed it. But as they did not seem to know much about anything, I was not unduly surprised. I mentioned our early attempts to explain the complementarity relationships by the assumption that, in the nucleic acid chain, adenylic was always next to thymidylic acid and cytidylic next to guanylic acid....I believe that the double-stranded model of DNA came about as a consequence of our conversation; but such things are only susceptible of a later judgment...."

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