What does the Ramachandran plot show?

What does the Ramachandran plot show?

• A. A plot of allowed phi and psi torsion angles for amino acid backbones.
• B. A map of side-chain dihedral angles chi1-chi5.
• C. A plot of bond lengths in the peptide backbone.
• D. A chart of amino acid residue frequencies in proteins.

Answer: (A)

The Ramachandran plot shows the allowed conformations of the protein backbone by mapping the two main backbone dihedral angles, phi and psi. Phi is the angle about the N–Cα bond and psi is the angle about the Cα–C′ bond. Because bulky atoms and the planar peptide bond create steric clashes, not every combination of these angles is possible, so only certain regions of the phi–psi space are energetically favorable. Those favored regions correspond to common secondary structures, such as alpha helices and beta sheets. It’s also why glycine, with its tiny side chain, has more allowed regions, while proline is more restricted due to its ring. This plot does not depict side-chain dihedral angles (chi angles), bond lengths, or residue frequencies, so the best description is that it maps allowed backbone torsion angles.

The Ramachandran plot shows the allowed conformations of the protein backbone by mapping the two main backbone dihedral angles, phi and psi. Phi is the angle about the N–Cα bond and psi is the angle about the Cα–C′ bond. Because bulky atoms and the planar peptide bond create steric clashes, not every combination of these angles is possible, so only certain regions of the phi–psi space are energetically favorable. Those favored regions correspond to common secondary structures, such as alpha helices and beta sheets. It’s also why glycine, with its tiny side chain, has more allowed regions, while proline is more restricted due to its ring. This plot does not depict side-chain dihedral angles (chi angles), bond lengths, or residue frequencies, so the best description is that it maps allowed backbone torsion angles.