Question: what are phi and psi angles?
Answer: The alpha carbon (Cα) in the center of each amino acid is held in the main chain by two rotatable bonds. The dihedral (torsion) angles of these bonds are called3 Phi and Psi (in Greek letters, φ and ψ). ... In fact, most Phi and Psi angle combinations are impossible because two atoms cannot occupy the same space.