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Picture n 51- DNA at X-Ray

X-ray diffraction diagram numbered 51 of the B form of DNA.  The dark cross let Watson and Crick know that the molecule was a double helix.  DNA (DeoxyriboNucleic Acid), the molecule that carries the genetic information, exists in two forms, A and B.  When in the B form, DNA is shielded in a sheath of water and thus, it is relatively free from the influence of neighboring molecules, the X-ray pattern being then, highly informative. (Image by Rosalind Franklin and Raymond Gosling, 1951. Caption adapted from Raquel Goncalves Maia, CFCUL)

Source: Watson, JD & Crick, FHC, Molecular Structure of Deoxypentose Nucleic Acids, Nature, Vol 171, pp 738-739, 25 April 1953

Link to different version of photo (here)

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