In 1951 and 1952, together with William Cochran and Vladimir Vand, Crick assisted in the development of a mathematical theory of X-ray diffraction by a helical molecule.
This theoretical result matched well with X-ray data for proteins that contain sequences of amino acids in the alpha helix conformation.
Helical diffraction theory turned out to also be useful for understanding the structure of DNA.

Late in 1951, Crick started working with James Watson at Cavendish Laboratory at the University of Cambridge, England.
Using "Photo 51" (the X-ray diffraction results of Rosalind Franklin and her graduate student Raymond Gosling of King's College London, given to them by Gosling and Franklin's colleague Wilkins), Watson and Crick together developed a model for a helical structure of DNA, which they published in 1953.
For this and subsequent work they were jointly awarded the Nobel Prize in Physiology or Medicine in 1962 with Wilkins.

When Watson came to Cambridge, Crick was a 35-year-old graduate student (due to his work during WWII) and Watson was only 23, but he already had a PhD They shared an interest in the fundamental problem of learning how genetic information might be stored in molecular form.
Watson and Crick talked endlessly about DNA and the idea that it might be possible to guess a good molecular model of its structure.
A key piece of experimentally-derived information came from X-ray diffraction images that had been obtained by Wilkins, Franklin, and Gosling.
In November 1951, Wilkins came to Cambridge and shared his data with Watson and Crick.
Alexander Stokes (another expert in helical diffraction theory) and Wilkins (both at King's College) had reached the conclusion that X-ray diffraction data for DNA indicated that the molecule had a helical structure—but Franklin vehemently disputed this conclusion.
Stimulated by their discussions with Wilkins and what Watson learned by attending a talk given by Franklin about her work on DNA, Crick and Watson produced and showed off an erroneous first model of DNA.
Their hurry to produce a model of DNA structure was driven in part by the knowledge that they were competing against Linus Pauling.
Given Pauling's recent success in discovering the Alpha helix, they feared that Pauling might also be the first to determine the structure of DNA.

Many have speculated about what might have happened had Pauling been able to travel to Britain as planned in May 1952.
As it was, his political activities caused his travel to be restricted by the United States government and he did not visit the UK until later, at which point he met none of the DNA researchers in England.
At any rate he was preoccupied with proteins at the time, not DNA.
Watson and Crick were not officially working on DNA.
Crick was writing his PhD thesis; Watson also had other work such as trying to obtain crystals of myoglobin for X-ray diffraction experiments.
In 1952, Watson performed X-ray diffraction on tobacco mosaic virus and found results indicating that it had helical structure.
Having failed once, Watson and Crick were now somewhat reluctant to try again and for a while they were forbidden to make further efforts to find a molecular model of DNA.

Of great importance to the model building effort of Watson and Crick was Rosalind Franklin's understanding of basic chemistry, which indicated that the hydrophilic phosphate-containing backbones of the nucleotide chains of DNA should be positioned so as to interact with water molecules on the outside of the molecule while the hydrophobic bases should be packed into the core.
Franklin shared this chemical knowledge with Watson and Crick when she pointed out to them that their first model (from 1951, with the phosphates inside) was obviously wrong.

Crick described what he saw as the failure of Wilkins and Franklin to cooperate and work towards finding a molecular model of DNA as a major reason why he and Watson eventually made a second attempt to do so.
They asked for, and received, permission to do so from both William Lawrence Bragg and Wilkins.
To construct their mod
In 1951 and 1952, together with William Cochran and Vladimir Vand, Crick assisted in the development of a mathematical theory of X-ray diffraction by a helical molecule. This theoretical result matched well with X-ray data for proteins that contain sequences of amino acids in the alpha helix conformation. Helical diffraction theory turned out to also be useful for understanding the structure of DNA.
Late in 1951, Crick started working with James Watson at Cavendish Laboratory at the University of Cambridge, England. Using "Photo 51" (the X-ray diffraction results of Rosalind Franklin and her graduate student Raymond Gosling of King's College London, given to them by Gosling and Franklin's colleague Wilkins), Watson and Crick together developed a model for a helical structure of DNA, which they published in 1953. For this and subsequent work they were jointly awarded the Nobel Prize in Physiology or Medicine in 1962 with Wilkins.
When Watson came to Cambridge, Crick was a 35-year-old graduate student (due to his work during WWII) and Watson was only 23, but he already had a PhD They shared an interest in the fundamental problem of learning how genetic information might be stored in molecular form. Watson and Crick talked endlessly about DNA and the idea that it might be possible to guess a good molecular model of its structure. A key piece of experimentally-derived information came from X-ray diffraction images that had been obtained by Wilkins, Franklin, and Gosling. In November 1951, Wilkins came to Cambridge and shared his data with Watson and Crick. Alexander Stokes (another expert in helical diffraction theory) and Wilkins (both at King's College) had reached the conclusion that X-ray diffraction data for DNA indicated that the molecule had a helical structure—but Franklin vehemently disputed this conclusion. Stimulated by their discussions with Wilkins and what Watson learned by attending a talk given by Franklin about her work on DNA, Crick and Watson produced and showed off an erroneous first model of DNA. Their hurry to produce a model of DNA structure was driven in part by the knowledge that they were competing against Linus Pauling. Given Pauling's recent success in discovering the Alpha helix, they feared that Pauling might also be the first to determine the structure of DNA.
Many have speculated about what might have happened had Pauling been able to travel to Britain as planned in May 1952. As it was, his political activities caused his travel to be restricted by the United States government and he did not visit the UK until later, at which point he met none of the DNA researchers in England. At any rate he was preoccupied with proteins at the time, not DNA. Watson and Crick were not officially working on DNA. Crick was writing his PhD thesis; Watson also had other work such as trying to obtain crystals of myoglobin for X-ray diffraction experiments. In 1952, Watson performed X-ray diffraction on tobacco mosaic virus and found results indicating that it had helical structure. Having failed once, Watson and Crick were now somewhat reluctant to try again and for a while they were forbidden to make further efforts to find a molecular model of DNA.
Of great importance to the model building effort of Watson and Crick was Rosalind Franklin's understanding of basic chemistry, which indicated that the hydrophilic phosphate-containing backbones of the nucleotide chains of DNA should be positioned so as to interact with water molecules on the outside of the molecule while the hydrophobic bases should be packed into the core. Franklin shared this chemical knowledge with Watson and Crick when she pointed out to them that their first model (from 1951, with the phosphates inside) was obviously wrong.
Crick described what he saw as the failure of Wilkins and Franklin to cooperate and work towards finding a molecular model of DNA as a major reason why he and Watson eventually made a second attempt to do so. They asked for, and received, permission to do so from both William Lawrence Bragg and Wilkins. To construct their mod
Francis Crick