What does a Ramachandran plot tell you?
The Ramachandran plot shows the statistical distribution of the combinations of the backbone dihedral angles ϕ and ψ. In theory, the allowed regions of the Ramachandran plot show which values of the Phi/Psi angles are possible for an amino acid, X, in a ala-X-ala tripeptide (Ramachandran et al., 1963).
What are the φ phi and ψ psi angles?
As with any peptide the conformation of the backbone is determined by the values of two torsional angles. In sequence order, phi (φ) is the C(i-1),N(i),Ca(i),C(i) torsion angle and psi (ψ) is the N(i),Ca(i),C(i),N(i+1) torsion angle.
What is phi and psi angles in Ramachandran plot?
The Ramachandran plot is a plot of the torsional angles - phi (φ)and psi (ψ) - of the residues (amino acids) contained in a peptide. In sequence order, φ is the N(i-1),C(i),Ca(i),N(i) torsion angle and ψ is the C(i),Ca(i),N(i),C(i+1) torsion angle.
What is the value of angle of φ and ψ for an alpha-helix and beta sheet?
Instead, it zig-zags in a more extended conformation than the alpha-helix. Amino acid residues in the beta-conformation have negative phi angles and the psi angles are positive. Typical values are phi = -140 degrees and psi = 130 degrees. In contrast, alpha-helical residues have both phi and psi negative.