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The Francis Crick Papers

Letter from Francis Crick to Jerry Donohue pdf (106,603 Bytes) transcript of pdf
Letter from Francis Crick to Jerry Donohue
Donohue published an article in the September 12, 1969, issue of Science (vol. 165, p. 1091), in which he questioned whether Fourier syntheses, a method for calculating the distribution of electron density from amplitudes (seen in X-ray diffraction images) and assumed bond angles of molecules in crystals--and thus a method for inferring the structure of such molecules--did in fact provide evidence for the Watson-Crick structure, specifically the base pairs, as DNA researchers like Maurice Wilkins claimed. Donohue in his article presented electron density maps of various combinations of base pairs which he claimed fit Fourier syntheses just as well as the canonical A=T and C=G pairs. He thereby implied that other base pairs and thus other structures for DNA were conceivable.
Crick, along with Maurice Wilkins and other DNA scientists, refuted Donohue's criticism and arguments in letters published in the March 27, 1970, issue of Science (vol. 167, p.1693). He did so again in this letter, challenging Donohue to further explain the results of his Fourier syntheses of his proposed base pairs.
In crystallography, a dyad (mentioned in the letter) is a two-fold symmetry, or a symmetry around two axes. A Patterson function is a technique developed in the 1920s for estimating the distances between atoms in a molecule by analyzing the intensities--the darkness--of the spots produced on a photographic plate by X-ray diffraction. This technique thus avoided the so-called phase problem in crystallography, the problem of measuring the X-rays' peaks and troughs, providing hints (though not conclusive evidence) of the internal structure of molecules.
Number of Image Pages:
1 (106,603 Bytes)
1970-05-20 (May 20, 1970)
Crick, Francis
Donohue, Jerry
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
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Medical Subject Headings (MeSH):
Crystallography, X-Ray
Exhibit Category:
Embryology and the Organization of DNA in Higher Organisms, 1966-1976
Metadata Record Letter from Jerry Donohue to Francis Crick (June 9, 1970) pdf (138,927 Bytes) transcript of pdf
Metadata Record Letter from Jerry Donohue to Francis Crick (May 6, 1970) pdf (171,829 Bytes) transcript of pdf
Box Number: 21
Folder Number: PP/CRI/D/2/11/1
Unique Identifier:
Document Type:
Letters (correspondence)
Physical Condition:
Series: Correspondence
SubSeries: Individual Correspondents
SubSubSeries: Correspondence: Donohue, Jerry
Folder: Correspondence with Donohue
20 May 1970
Dear Jerry
Thank you for your letter of May 6. I am amused to see from it that, as I suspected, you have not appreciated the point about the dyads in the DNA model.
Of course, it is quite possible to make errors with centric Fouriers, but it is the general experience of crystallographers, and I am sure it is yours, that it is much easier to do so with acentric structures. I think you have quite failed to appreciate the significance of this difference and also that it is far harder to get false structures from polymers than from single crystals of small molecules. You are only likely to get an "acceptable" false structure if its Patterson is similar to the Patterson of the real structure, and the much greater restrictions imposed by a polymer make this condition more difficult to satisfy.
Would you please explain to me the following odd circumstances, which must have struck the attentive reader of Science? Whenever the King's College group do a difference synthesis it shows clearly the direction the groups of atoms should be moved. Whenever you publish the synthesis of one of your imaginary structures of base pairs, it is difficult to distinguish the false solution from the true one and the difference synthesis does not show clearly how the groups of atoms should be moved. I feel that I can explain this rather remarkable difference. Can you?
I look forward with interest to your reply.
F.H.C. Crick
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