The plot of the torsional angles of the amino acid residues in a peptide is called the Ramachandran plot. The two torsional angles are the phi (φ)and psi (ψ). The phi (φ) is formed between the nitrogen and the α-carbon atom (N-Cα) while the psi (ψ) is formed between the α-carbon and the carbon atom of the carbonyl group (Cα-C).
