Dihedral angles in glutamate: Dihedral angles are the main degrees of freedom for the backbone (ϕ and ψ angles) and the side chain (χ angles) of an amino acid. The number of χ angles varies between zero and four for the 20 standard amino acids. The figure shows a ball-and-stick representation of glutamate, which has three χ angles. The fading conformations in the background illustrate a rotation around χ1. The figure was made using PyMOL http://www.pymol.org.