Chapter4_BCH461-part1

Chapter4_BCH461-part1 - Chapter 4 The Three-dimensional...

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Chapter 4 The Three-dimensional Structure of proteins Overview of protein structure Secondary Structure Tertiary Structure Subunit Interactions and Quaternary Structure Protein Denaturation and Folding
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Formation of Peptide Bond
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The Coplanar Nature of the Peptide Bond Six atoms of the peptide group lie in a plane!
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The trans peptide group: Successive C α group are on opposite sides of the peptide bond joining them. The peptide group has a rigid, planar structure as a consequence of resonance interactions that give the peptide bond ~40% double-bond character.
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Summary of the Peptide Bond •is usually found in the trans conformation •has partial (40%) double bond character •due to the double bond character, the six atoms of the peptide bond group are always planar! •peptide bond is polar: N partially positive; O partially negative
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Three Bonds Separate Sequential α -Carbons in a Polypeptide Chain. Only the C α -N and C α -C Bonds can Rotate.
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Torsion angles • Two degrees of freedom per residue for the peptide chain • Angle about the C α -N bond is denoted phi ( φ ) • Angle about the C α -C bond is denoted psi ( ψ ) • The entire path of the peptide backbone is known if all phi and psi angles are specified
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phi ( φ ) (about C α -N) (-180 — 180 °) and psi ( ψ ) (about C α -C) (-180 — 180 °) Angles
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Chapter4_BCH461-part1 - Chapter 4 The Three-dimensional...

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