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Chapter06 - BCH 4053 Spring 2003 Chapter 6 Lecture Notes...

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Chapter 6, page 1 BCH 4053 Spring 2003 Chapter 6 Lecture Notes Slide 1 CHAPTER 6 Proteins: Secondary, Tertiary, and Quaternary Structure Slide 2 Levels of Protein Structure Primary (sequence) Secondary (ordered structure along peptide bond) Tertiary (3-dimensional overall) Quaternary (subunit relationships) Slide 3 Forces Contributing to Overall Structure Strong (peptide bond, disulfide bond) • Weak Hydrophobic (40 kJ/mol) Ionic bonds (~20 kJ/mol) Figure 6.1 Hydrogen bonds (~12-30 kJ/mol) Dispersion (van der Waals) (0.4-4 kJ/mol)
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Chapter 6, page 2 Slide 4 Effect of Sequence on Structure Sufficient information for folding into correct 3-dimensional structure is in the sequence (primary structure) of the protein Experiments of Anfinsen and White on Ribonuclease However—the “folding problem” is one of the major unsolved problems of biochemistry and structural biology Slide 5 Secondary Structure Folding probably begins with nucleation sites along the peptide chain assuming certain stable secondary structures. Planarity of the peptide bond restricts the number of conformations of the peptide chain. Rotation is only possible about the C(alpha)-N bond (the Φ (phi) angle) C(alpha)-C bond (the Ψ (psi) angle) See Figure 6.2 Slide 6 Steric Constraints on Φ and Ψ Angles Examine the effects of rotation about the Φ and Ψ angles using Kinemage Download Kinemage Download Peptide file Note that some angles are precluded by orbital overlap: Figure 6.3
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