= Alpha helix
{title2=$\alpha$}
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= Alpha helices
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An <alpha helix> is a coiled <protein secondary structure> with a repeated pattern of <backbone hydrogen bonds>. In the standard pattern, the backbone group of <amino acid residue> $i$ bonds to that of residue $i+4$: for example, positions 2 and 6. This is an additional spatial interaction, not a replacement <peptide bond> between those positions. Pauling, Corey and Branson proposed the helical arrangement in their 1951 paper by reasoning from the geometry of small <molecules>. See https://williams.chemistry.gatech.edu/course_Information/6572/papers/pauling_1951_helix.pdf[Pauling, Corey and Branson, The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain, PNAS 37, 205–211 (1951)].
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