ch03 - 1/31/2011 Chapter3 AminoAcidsandPeptides

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1/31/2011 1 Chapter 3 Amino Acids and Peptides Proteins play a critical role in almost every biological process Proteins play a critical role in almost every biological process: enzymatic catalysis transport and storage of smaller molecules and ions coordinated motion micro and macroscopic structural support and integrity, primarily collagen and elastin immune response generation and transmission of nerve impulse growth and development control substrate for metabolism Is the carbon a chiral center? Side chain nomenclature 3 2
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1/31/2011 2 Recall, non superimposable mirror images are enantiomers 3 3a (S) (R) The RS configuration of L alanine is shown perspective 3 3 Fischer projection
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1/31/2011 3 All D HIV protease is mirror image of natural L HIV protease Science 256 :1403, 1455 (1992) “zwitterion” Acid/base properties of the amino acid back bone low pH neutral pH high pH
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1/31/2011 4 Isoelectric point, Titration profile for glycine pI pK 1 pK 2 2 3 10 pKa values for α amino and carboxylic acids are perturbed
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1/31/2011 5 Titration profile for glutamic acid 1 2 pI pK COOH pK R 2 2.19 4.25 2 3 22 +1 0 3.22 3 12a What is the net charge of the species at this position? pK R = 8.2 What role might the hydroxyl groups of ser and thr play in protein structure? 3 5 Unlike all other L aa, L cys has R configuration. Why? H bonding CH 2 SH has higher priority than COOH
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1/31/2011 6 In forming the disulfide, cysteine side chains are oxidized 3 7 sulfhydryl disulfide pK R = 4.2 pK R = 3.7 3 5 Asp has a shorter “insulating” side chain placing carboxylic acid nearer ammonium and rendering it slightly more acidic.
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1/31/2011 7 pK R = 10.5 pK R = 12.5 pK R = 6.0 3
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This note was uploaded on 05/01/2011 for the course CH 53890 taught by Professor Raymonds during the Spring '09 term at University of Texas at Austin.

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ch03 - 1/31/2011 Chapter3 AminoAcidsandPeptides

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