Editing Francis Crick (section)

===1949–1950===
Crick taught himself the mathematical theory of X-ray crystallography.<ref name=CrickWMP46>[[#Crick|Crick (1990)]], p. 46: "there was no alternative but to teach X-ray diffraction to myself."</ref> During the period of Crick's study of [[X-ray]] [[diffraction]], researchers in the Cambridge lab were attempting to determine the most stable helical conformation of [[amino acid]] chains in proteins (the [[alpha helix]]). Linus Pauling was the first to identify<ref>{{Cite journal|vauthors=Pauling L, Corey RB |title=Atomic Coordinates and Structure Factors for Two Helical Configurations of Polypeptide Chains |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=37 |issue=5 |pages=235–40 |date=May 1951 |pmid=14834145 |pmc=1063348 |doi=10.1073/pnas.37.5.235|bibcode = 1951PNAS...37..235P |url=http://authors.library.caltech.edu/10215/1/PAUpnas51g.pdf |archive-url=https://web.archive.org/web/20170922115158/http://authors.library.caltech.edu/10215/1/PAUpnas51g.pdf |archive-date=2017-09-22 |url-status=live |doi-access=free }}</ref> the 3.6&nbsp;amino acids per helix turn ratio of the alpha helix. Crick was witness to the kinds of errors that his co-workers made in their failed attempts to make a correct molecular model of the alpha helix; these turned out to be important lessons that could be applied, in the future, to the helical structure of DNA. For example, he learned<ref name="CrickWMP58">[[#Crick|Crick (1990)]], p. 58</ref> the importance of the structural rigidity that [[cis–trans isomerism|double bonds]] confer on molecular structures which is relevant both to [[peptide bond]]s in proteins and the structure of [[nucleotide]]s in DNA.