In the Ramachandran plot, each dot represents an observed pair of angles in a protein (Richardson J. The conformation of the main-main atoms in a protein is determined by one pair of phi et psi angles for each amino acid because of steric collisions within each amino acid, most pairs of phi and psi angles do not occur. C bond, whose angle of rotation is called psi (Ψ). the peptide bond is planar and does not permit rotation.īond, whose angle of rotation is called phi (φ).Peptide bondsĮach amino acid contributes three bonds to its polypeptide chain Steric limitations on the bond angles in a polypeptide chain.
