User:Stephen Mills/Sandbox 4 Secondary Structure: Helices XU

From Proteopedia

The α-helix

α-helices are the most common type of regular helix found in proteins. They are characterized by the following helix parameters:

Dihedral angles: Φ ~ -60^o, φ ~ -45^o

Repeat (number of residues per turn) = 3.6

Rise (translation along axis per amino acid residue) = 1.5 Angstroms (0.15 nm)

Twist (rotation around axis per amino acid residue) = 100^o (= 360^o/repeat)

Pitch (translation along axis per turn) = 5.4 Angstroms (= 0.54 nm = Repeat x Rise)

The helix shown below is a 19 amino acid chain in α-helical conformation.

All the atoms are shown in this initial orientation (C = green; N = blue; O = red; S = yellow; H = white). The helix axis runs vertically, approximately parallel to the plane of the screen.