Question #85996

Explain the stereochemistry of peptide bond.What do the φ and ψ angles signify in peptides?

Expert's answer

*α*-N bonds have an angle of rotation and , respectively. Due to the partially dual nature of the C – N bond, the angle *ω* is 180 °. Therefore, the conformational capabilities of the polypeptide chain are determined by the set of angles *ψ* and *ϕ*. The values of angles *ψ* and *ϕ* provide complete information about the spatial structure of the main protein chain. Graphically, the conformational parameters of a polypeptide chain are usually depicted using maps proposed by Ramachandran in 1963. These maps reflect the dependence of the energy of the amino acid residue on the parameters *ψ* and *ϕ*. The angles *ψ* and *ϕ* are plotted along the coordinate axes from –180 ° to + 180 °. Due to the interaction between the side chains, these angles cannot take on any values . Only specific discrete regions are allowed for them, which correspond to the energetically favorable conformations of the polypeptide chain representing the are areas of minimum energy.

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