History of chemistry quantum mechanics were able to predict qualitatively some chemical features for biologically relevant molecules, they were, till the end of the 20th century, more a collection of rules, observations, and recipes than rigorous ab initio quantitative methods. This heuristic approach triumphed in 1953 when James Watson and Francis Crick deduced the double helical structure of DNA by constructing models constrained by and informed by the knowledge of the chemistry of the constituent parts and the X-ray diffraction patterns obtained by Rosalind Franklin. This discovery lead to an explosion of research into the biochemistry of life. In the same year, the
Francis Crick to peptide bonds in proteins and the structure of nucleotides in DNA. 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