ch03.1 - Chapter 3 Amino Acids and Peptides Proteins play a...

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Unformatted text preview: Chapter 3 Amino Acids and Peptides 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 impulses substrate for metabolism Which of the following amino acids has a net negative charge at pH 7.0? A. glycine B. threonine C. aspartate D. arginine 3-2 Is the carbon a chiral center? 3-3a Non-superimposable mirror images = enantiomers What is the RS confguration oF L-alanine? S 3-3 perspective Fischer projection 3-4 D, L System : stereoisomers related to L-glyceraldehyde are designated L Science 256 :1403, 1455 (1992) All D-HIV protease is mirror image of natural L-HIV protease R C COOH H NH 3 + R C COO- H NH 2 R C COO- H NH 3 + H + H + Proton donor (acid) Proton acceptor (base) zwitterion Is the amino acid acting as an acid or a base here? Acid/base properties of amino acids Amino acids are amphoteric compounds (or ampholytes) -- they can act as either an acid or a base What parameter infuences the ionization state oF a molecule? pH 3-10 pI = pK 1 + pK 2 2 What do we call an acid with 2 ionizable protons? Diprotic acid Titration curve for amino acid glycine - 2 stages Isoelectric point For amino acid without ionizable R group: Net charge is zero-- one group completely ionized next group just beginning Why is carboxyl group of amino acid more strongly dissociated (10 - 100-fold) than carboxyl group of simple monocarboxylic acids like acetic acid? (pK 2.3 vs....
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This note was uploaded on 11/02/2009 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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ch03.1 - Chapter 3 Amino Acids and Peptides Proteins play a...

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