# Alpha helix (rotational angle)

## Description

The alpha helix (α-helix) is a common secondary structure of proteins and is a righthand-coiled or spiral conformation (helix). Residues in α-helices typically adopt backbone (φ, ψ) dihedral angles around (-60°, -45°). they adopt dihedral angles such that the ψ dihedral angle of one residue and the φ dihedral angle of the next residue sum to roughly -105. The general formula for the rotation angle Ω per residue of any polypeptide helix with trans isomers is depended of the (φ, ψ) dihedral angles.

Related formulas## Variables

Ω | The the rotation angle (degrees) |

ϕ | Dihedral angle of one residue ( angle between two planes) (degrees) |

ψ | Dihedral angle of the next residue ( angle between two planes) (degrees) |