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Answer to Question #85996 in Biochemistry for Dinesh Kurmi

Question #85996
Explain the stereochemistry of peptide bond.What do the φ and ψ angles signify in peptides?
Expert's answer

The peptide group and its properties determine the conformational capabilities of the polypeptide chain. The geometry of the polypeptide chain is determined by a set of rotation angles. Three consecutive С@$\alpha@$-С, С-N, and Сα-N bonds have an angle of rotation @$\psi, \omega@$ and @$\phi@$, 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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