Alpha helix

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The alpha helix is the name given to the way that the secondary structure of a polypeptide chain can be folded. Its structure was proposed in 1951 by Linus Pauling and Robert Corey through research on alpha-keratin, a protein common in skin, hair and nails; within a year they also discovered the beta pleated sheet.

The alpha helix was proposed to have a rod like structure and when coiled up it had a similar appearance to that of DNA presented by Watson and Crick. The inside of the helix consists of the tightly coiled backbone with the side chains (R Group) of the amino acids extending outwards. The helix is held together by hydrogen bonds which are between the NH and the CO groups of the amino acids. As the helix is tightly coiled there are 3.6 amino acid residues per turn and each residue is a traslation of 1.5 Angstroms and a rotation of 100 degrees. The alpha helix can either have a clockwise or anticlockwise screw sense[1][2].

Keratin is a molecule that exhibit an alpha helix, multiple Keratin molecules can coil together to become supercoiled.


  1. Berg J.,Tymoczko J.,Stryer L.,(2010)Biochemistry,7th Edition,New York(USA):W.H.Freeman and Company, pgs 38,39
  2. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P, Molecular Biology of the Cell, 5th Edition. New York (USA), Garland Science, 2008, page 131

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