The scientist Linus Pauling was eager to solve the mystery of the shape of DNA. In 1954 he became a Nobel Laureate in Chemistry for his ground-breaking work on chemical bonds and the structure of molecules and crystals. In early 1953 he had published a paper where he proposed a triple-helical structure for DNA. Watson and Crick had also previously worked out a three-helical model, in 1951. But their theory was wrong.
Their mistake was partly based on Watson having misremembered a talk by Rosalind Franklin where she reported that she had established the water content of DNA by using X-ray crystallographic methods. But Watson did not take notes, and remembered the numbers incorrectly.
Instead, it was Franklin's famous "photograph 51" that finally revealed the helical structure of DNA to Watson and Crick in 1953. This picture of DNA that had been crystallized under moist conditions shows a fuzzy X in the middle of the molecule, a pattern indicating a helical structure.
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