James Watson diffraction data collected by Rosalind Franklin and Raymond Gosling. The controversy arose from Watson and Crick using some of Franklin's unpublished data—without her consent—in their construction of the double helix model of DNA. Franklin's experimental results provided estimates of the water content of DNA crystals and these results were consistent with the two sugar-phosphate backbones being on the outside of the molecule. Franklin personally told Crick and Watson that the backbones had to be on the outside, which was a crucial piece of information; before then, Linus Pauling and Watson and Crick had generated erroneous models with the chains inside
History of molecular biology modeling efforts of Watson and Crick. In their modeling, Watson and Crick restricted themselves to what they saw as chemically and biologically reasonable. Still, the breadth of possibilities was very wide. A breakthrough occurred in 1952, when Erwin Chargaff visited Cambridge and inspired Crick with a description of experiments Chargaff had published in 1947. Chargaff had observed that the proportions of the four nucleotides vary between one DNA sample and the next, but that for particular pairs of nucleotides — adenine and thymine, guanine and cytosine — the two nucleotides are always present in equal proportions. Using X-ray diffraction, as