Tutorial 2 - BCH210 Friday Tutorial Week Two David Tulumello

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BCH210 Friday Tutorial Week Two David Tulumello david.tulumello@utoronto.ca
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BCH210 Week 2 Protein Backbone angles Ramachandran Plots Fibrous Proteins Silk, keratin, collagen Globular Proteins Membrane Proteins Protein Folding Anifsen’s experiment
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Protein Organization Four Levels of Protein Structure Primary Structure Linear sequence of amino acids Secondary Structure Local regularities induced by hydrogen bonding . -helix, -sheet Tertiary Structure Completely folded polypeptide Quaternary Structure Association of two or more polypeptide chains
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How do proteins adapt structure?
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Amino Acid Conformation The peptide bond has some double bond character Resonance with carbonyl oxygen
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Amino Acid Conformation Resonance makes the peptide bond planar trans - two -carbons on alternate sides of peptide bond cis - two -carbons on same side of peptide bond Almost all peptide bonds are trans due to steric hindrances
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Amino Acid Conformation Rotation is still possible around both bonds to the α - carbon N-C --> phi or C -C --> psi or Values: -180° to +180 ° +ve = clockwise -ve = counterclockwise The and are sufficient to describe the relative position of the four atoms: C - N - C - C
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Amino Acid Conformation N-C --> phi or C -C --> psi or
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Amino Acid Conformation Ramachandran plot o Mathematical model of which and angles are permissible o Residues with large side chains have more restricted rotation due to steric interactions Glycine most free (R = -H) Proline angle limited (-60° to -77°) due to cyclical side chain
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Alpha Helix ( , ) = (-60, -50) Beta Sheet ( , ) = (-140, +135) Ramachandran Plots
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Ramachandran Plots of Amino Acids in Proteins Ala Arg Gly ??? Ψ Φ
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Fibrous Proteins Silk Stacked Beta Sheets Keratin Colied-coil Alpha Helicies Collagen Colied-coil polyproline helicies
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Fibrous Proteins--Silk Composition: 44.6% glycine, 29.5% alanine, 12.2% serine Sequence: Gly-Ser-Gly-Ala-Gly-Ala repeats Silk is a -sheet protein
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Fibrous Proteins--Silk Small residue glycine allows tight packing between sheets Rotate 90 0
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Fibrous Proteins--Keratin Composition: 11.2% Cysteine, Low-sulfur (skin) vs. high- sulfur (horns) Sequence: nonpolar-X-X-X-X-X-nonpolar Keratin is an -helical coiled coil Top View
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Fibrous Proteins--Keratin Wool can be stretched (alpha-helix stretches) Unwinding of coiled-coil α -helix to β -sheet transition Disulfide crosslinks are the main restoring force
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This note was uploaded on 11/23/2010 for the course BCH BCH210 taught by Professor Deber during the Fall '08 term at University of Toronto- Toronto.