mcb450(5+6)

mcb450(5+6) - Lecture 5 (Chapter 5 & 6) Protein...

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Unformatted text preview: Lecture 5 (Chapter 5 & 6) Protein Structure & Protein Folding Assignment : 9 problems Jaya Sarkar ; Office hrs: Monday and Tuesday 3 to 4 PM Outline Protein structure (1, 2, 3, 4) Protein folding (formation of 3 structure) Protein denaturation Isolation and purification of proteins from cells Determination of amino acid sequence of a protein Relationship between proteins Post-translational modifications in proteins Ligand binding by proteins Protein structure Protein structure is defined in FOUR levels of organization: Primary (1), Secondary (2), Tertiary (3) and Quarternary (4) 1 2 3 4 Maintained by covalent bonds Maintained by weak, non covalent interactions 3 -for functional protein Protein structure Primary (1): The amino acid sequence of a protein Primary structure maintained by covalent bonds C-terminus N-terminus Disulfide bonds (intrachain) Ribonuclease A (124 amino acids) Protein structure Secondary (2): Regular sub-structures formed through H-bonding interactions between adjacent residues in a polypeptide chain. When a number of H-bonds form, the polypeptide chain can thus arrange itself into two kinds of 2 structure:- -Helix- -strand -Helix -strand Protein structure Tertiary (3): The polypeptide protein chains bend in 3D space to adopt a compact 3D shape/structure. Such a globular shape minimizes surface:volume ratio, ensuring that the protein interactions with the environment are minimal -sheet -Helix Tertiary level of protein structure results from folding into a roughly globular shape Knowledge of location of every atom in space: results from X-ray crystallographic studies Protein structure Quarternary (4): Many proteins consist of multiple polypeptide chains, called subunits. Organization of folded multiple polypeptide chains via non-covalent interactions results in the quarternary level of protein structure Hemoglobin: consists of 4 polypeptide chains / subunits-H-bonds-Hydrophobic Interactions-Ionic (electrostatic) Interactions-Van der Waals Interactions Forces governing protein structure Lys Asp Non-covalent interactions stabilize the higher orders (2, 3 and 4) of protein structure Ser Asp (between side chains) Val Val Forces governing protein structure: H-bonding H-bonds form whenever possible: The peptide backbone atoms H-bond with one another . For example in helices, the C=O and the NH group of every interior residue participate in H-bonds Side chains capable of forming H-bonds are usually located on protein surface so that they can H-bond with water molecules and also with surface side chains of other protein molecules. H-bonding in the interior of a protein can provide substantial stabilization to the protein Although each H-bond contributes only a few kJ/mol to the stabilization of a protein, the number of H-bonds formed in a protein is typically very large and hence the total stabilization due to H-bonds is substantial H-bonding...
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mcb450(5+6) - Lecture 5 (Chapter 5 & 6) Protein...

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