L05-2011 Proteins3

L05-2011 Proteins3 - Le cture5 Protein Structure Proteins...

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Membrane Proteins Begin proteins as membrane transporters Lecture 5 Enzyme function Binding sites Free energy Activation energy, enzyme function Proteins as enzymes Protein Structure
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1˚ structure: the linear sequence of amino acids N-terminal to C-terminal 2 structure ˚ : stretches of the polypeptide chain that fold into α -helix or β -sheet ( H-bonding ) 3 structure ˚ : 3-dimensional conformation of a single polypeptide chain 4 structure ˚ : multiple polypeptide chains interacting to form a complex 4 Levels of Protein Structure Polypeptide is not the same as a protein
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1 structure = sequence of amino acids ˚ ECB 4-2 With 20 possible a.a. at each site, nearly infinite number of polypeptide sequences are possible Allows proteins to have diverse functions Typical polypeptides are 50 – 2000 amino acids long
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Higher levels of organization are determined by polypeptide folding In addition to covalent bonds, folding determined by H bonds, ionic bonds, van der Waals interactions and hydrophobic interactions Flexibility of the backbone allows polypeptides to fold into higher order structures Hydrophobic interactions help proteins fold Polypeptides in cytosol usually fold to an energy minimum; hydrophilic aa out, hydrophobic aa inside
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Improper protein folding is associated with disease Alzheimers and Huntingtons diseases - aggregated proteins in brain Prion diseases - scrapie (sheep), mad cow (bovine), chronic wasting disease (deer, elk), Creutzfeldt-Jacob disease (CJD, humans) Misfolding spreads rapidly from cell to cell in brain ECB 4-8
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1˚ structure: the linear sequence of amino acids N-terminal to C-terminal 2 structure ˚ : stretches of the polypeptide chain that fold into α -helix or β -sheet ( H-bonding ) 3 structure ˚ : 3-dimensional conformation of a single polypeptide chain 4 structure ˚ : multiple polypeptide chains interacting to form a complex 4 Levels of Protein Structure Polypeptide is not the same as a protein
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α -helix and β -sheet Folding due to hydrogen bonds between atoms of peptide bonds (Recall N-H and C=O are polar covalent bonds; form H bonds) Therefore, can form α -helix and β -sheet from many different primary sequences Secondary Structure Within a single polypeptide chain Where are + and -?
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α helix H bond between C=0 and N-H 4 a.a. apart H bond R groups are on outside of helix Right handed helix ECB 4-10 α helices are common in regions of proteins that span lipid bilayer ECB 4-10
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β -sheet H bond between adjacent sections 1 polypeptide! ECB 4-10 β -sheet gives silk its strength Parallel N C C N N C Antiparallel N C N C N C
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Multiple types of chemical “bonds” stabilize the tertiary conformation of polypeptides Weak bonds: Ionic bonds between amino acid side chains H-bonds between amino acid side chains Hydrophobic interactions Nonpolar side-chains buried in interior away from water Polar/charged side chains out to
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This note was uploaded on 02/01/2011 for the course BIO 2020 taught by Professor Kropf during the Spring '11 term at Utah.

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L05-2011 Proteins3 - Le cture5 Protein Structure Proteins...

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