Alpha helix

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 along with 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