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L5-7_3D_Structure_of_Proteins - Lectures 5-7 The 3-D...

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22 Lectures 5-7 The 3-D Structure of Proteins 3-D structure is what gives proteins their functions theoretically speaking, a protein should be able to take on unlimited conformations there are hundreds of single bonds allowing free rotation instead, observation of protein structures shows that each protein has a certain three- dimensional structure when examining several protein structures, five themes become apparent 1. The amino acid sequence determines the protein’s structure 2. The function of a protein depends on its structure 3. An isolated or purified protein usually exists in one or a small number of stable structural forms 4. Non-covalent interactions are the primary interactions that hold a proteins 3-D structure 5. Common structural patterns appear in all proteins. a number of forces or structural features influence the 3-D structure of a protein character of the peptide bond hydrogen bond interactions charge interactions hydrophobic interactions Overview the arrangement of the atoms in a protein is its conformation any change in this arrangement is a conformational change does not describe a particular change, but just any change the conformation that predominates under a given set of conditions are typically the most thermodynamically stable (lowest free energy –G) the functional, folded conformation is the native conformation the native conformation is not very stable held together mainly by weak interactions G of 20-65 kJ/mol between folded and unfolded states 1 gallon of gasoline contains about 31,000 kcal = 129,704 kJ 1 mol of a 29,000 MW protein = 29,000 g = 63.9 lb to get 20 – 65 kJ from gasoline, only 0.6 – 1.95 ml are required to get 20 – 65 kJ from a protein, you have to fold 63.9 lb of a 29 kD protein for comparison to break a covalent bond requires 200 – 460 kJ/mol o one mole of covalent bonds in glucose (C 6 H 12 O 6 ) in 8.18 g of glucose Levels of Protein Structure Primary (1°) Structure: the amino acid sequence Secondary (2°) Structure: the stable local conformation of some part of the peptide Tertiary (3°) Structure: the arrangement of the 2° structural features within a polypeptide (protein)
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L5-7_3D_Structure_of_Proteins - Lectures 5-7 The 3-D...

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