4- Protein Structure 1

4- Protein Structure 1 - 580.221-Lecture 4Fall 20081P t...

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Unformatted text preview: 580.221-Lecture 4Fall 20081P t iSttdFtiPut your name, section number and TA on your HW. Please put your HW in correct pile (by section)Protein Structure and FunctionEileen HaaseFall 2008‐Lecture #41Structure leads to function•Proteins are made of sequences of aminoacids bound together through covalentpeptide bonds•The sequence of amino acids leads to thetwisting and folding of the protein into its finalshape•Protein shape determines what and howstrongly the protein binds to itself and othermolecules.2Protein structure34Protein Folding is a Reactioninvolving weak forcesunfolded<==> folded][lnGGofoldfoldunfoldedfoldedRT5Gfold =Hfold - TSfold= Gweak forces= (Hi - TSi)Final Protein Structure•MinimizeG–Protein will twist and fold in a manner thatminimizes energy.Final structure is usually unique “native”•Final structure is usually unique,native•Replacement of a single amino acid in aprotein with hundreds of amino acids cantotally change the structure, and consequentlyfunction, of the protein6580.221-Lecture 4Fall 20082Binding depends upon the3‐Dstructure ofa molecule7Replacing an amino acid in the binding region mayhave a huge effect on the ability of an antibody to bind an antigen.Replacing an amino acid at a different site might nothave an effect on binding or function.4 levels of protein structure•Primary: sequence of amino acids (NH2COOH)•Secondary:‐helix and‐pleated sheet•Tertiary: domains from multiple secondarystructures•Quaternary: Subunits formed from multiplepeptides8Amino Acids differ only in theirside chains‐20 total9Carbon can bind 4 different molecules resultingin two stereoisomers: L and D‐Carbonis center of the amino acid10CO-R-N,Clockwise with Hvisible towards you11General Reaction to make macromolecules12580.221-Lecture 4Fall 20083Polymers made through condensation13Formation of peptides20 different amino acids can make 10-50K proteins, 14all using the same peptide bondIt takes energy to make a peptide bond(G>0)15Peptide bond: OH of carboxyl group combines with H from amino groupEvery type of amino acid uses peptide bonds16Side chains are not involved in peptide bond: stay the same•Peptide is a straight chain with side groups•The C-molecules are in a plane •amino on left (N) and carboxyl on right (C)• R groups determine 3-D folding caused by 4 weak forces17Amino endCarboxyl end-CarbonsAmino Acid structure depends upon pHRAt pH = 7, how many molecules are ionized? Use the Henderson-Hasselbach Equation: pH = pK + log [A-]/[HA] 10...
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4- Protein Structure 1 - 580.221-Lecture 4Fall 20081P t...

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