A portion of secondary structure that looks like a spiral staircase. More so than DNA even, as it is single stranded. Think of the bannister as the backbone, with poles joining one portion of the rail to the section directly above. This right handed helix has a pitch of 0.54 nanometers (10 to -9 M)and a 36 residue helix turns 10 times. Therefore the rise is 0.15 nm per residue.

Left handed (pi) helices are also possible, but are less stable and therefore shorter. A three-ten helix is not uncommon; the name referring to the residues per turn (3) and the number of residues in the hydrogen bonded loop(10). In this sense, an alpha helix is a 3.6 - 13 helix.

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