Dihedral Angles in Polypeptide Chain Single Bonds

Dihedral angles specify the torsional rotation about the C-alpha bonds. Single bonds in a polypeptide chain have dihedral angles called: called phi and psi. While the possibilities for phi and psi seem infinite, steric strain or steric collision between amino acid side chains eliminates many combinations of phi and psi. Ramachandran, a physicist who studied protein structure, created a two-dimensional diagram call the Ramachandran plot to visualize favorable combinations of phi and psi.

• The angle of rotation about the carbon-nitrogen bond between the alpha carbon and the amino group.

• The angle of rotation about the carbon-carbon bond between the alpha carbon and the carboxyl group.