chapter4 notes

chapter4 notes - Chapter 4- Protein structure and function...

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Chapter 4- Protein structure and function Proteins constitute most of the dry mass of the cell Different types: enzymes (ex. DNA polymerase), structural proteins (ex. Keratins), transport (ex. Hemoglobin), motor proteins (ex. Myosin, kinesin), storage (ferritin), signaling (ex. Insulin), receptors (ex. Rhodopsin), gene regulatory proteins Structure of a protein (amino acid sequence and conformation) determines its function Amino acid sequence determines 3D protein structure determines protein function
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Amino Acid – building block for proteins
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Amino Acids – the building block for polypeptides (proteins)
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- Proteins (Polypeptides) - long chains of amino acids (polymers) - amino acids in proteins are linked by covalent bonds called peptide bonds
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04_03_20 amino acids.jpg Amino Acids have different R groups and different characteristics
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Protein shape (Conformation) Shape of a protein (also called a polypeptide) is specified by the sequence of amino acids with their specific R groups Long polypeptide chains are very flexible (many of the carbon atoms in the backbone are free to rotate) Each polypeptide folds in a characteristic way due to interactions between atoms in both the backbone and the R groups of the amino acids Proper protein folding is crucial – if wrong the protein can form aggregates that damage cells – these underlie a number of neurogenerative disorders inclduing Alzheimer’s disease and Huntington’s disease, and prion diseases such as mad cow disease Each polypeptide will fold up into a particular conformation that will be constrained by lots of weak non-covalent bonds Bonds between atoms in backbone and side chain Bonds are H bonds, ionic bonds, van der Waals, hydrophobic interactions
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04_04_noncovalent.jpg
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04_05_Hydrophobic.jpg Hydrophobic interactions help proteins fold into compact shapes
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04_06_Hydrogen bonds.jpg
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Protein folding Many possible conformations that a protein could fold into But, for proteins found in cells, usually just one protein conformation is found (it is essential that a protein folds up properly each time) Proteins always fold into the conformation of lowest energy Each protein has a particular # and order of aa’s The protein will fold up in a way that minimizes the free energy
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Protein folding cont. For a protein 300 aa’s long, 20 300 possibilities Most of these will not adopt a single, stable 3D structure Proteins found in cells almost always adopt a unique stable conformation
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04_07_Denatured prot.jpg Denaturation – loss of conformation Renaturation – proper refolding after denaturing agent is removed Thus the amino acid sequence has all the information needed for proper folding proteins can often fold up correctly without help in the cell, special proteins called molecular chaperones assist folding of other proteins Chaperones make folding more efficient by preventing association with wrong partners in the crowded cytoplasm
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04_09_Proteins.jpg Proteins come in a variety of shapes and sizes Their shape determines their function
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This note was uploaded on 02/08/2012 for the course BIOL 302 taught by Professor Connollyandkrizek during the Spring '08 term at South Carolina.

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chapter4 notes - Chapter 4- Protein structure and function...

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