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chapter3 RKW - Lecture Connections 3 | Amino Acids Peptides...

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Lecture Connections 3 | Amino Acids, Peptides, Proteins © 2009 W. H. Freeman and Company
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CHAPTER 3 Amino Acids, Peptides, Proteins Structure and naming of amino acids Structure and properties of peptides Ionization behavior of amino acids and peptides Methods to characterize peptides and proteins Learning goals :
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Proteins: Main Agents of Biological Function Catalysis: –enolase (in the glycolytic pathway) DNA polymerase (in DNA replication) Transport: –hemoglobin (transports O 2 in the blood) lactose permease (transports lactose across the cell membrane) Structure: collagen (connective tissue) keratin (hair, nails, feathers, horns) Motion: –myosin (muscle tissue) actin (muscle tissue, cell motility)
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Amino Acids: Building Blocks of Protein Proteins are heteropolymers of α -amino acids Amino acids have properties that are well suited to carry out a variety of biological functions: Capacity to polymerize Useful acid-base properties Varied physical properties Varied chemical functionality
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Amino Acids: Atom Naming Organic nomenclature: start from one end Biochemical designation: start from α -carbon and go down the R-group
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Most α -Amino Acids are Chiral The α -carbon has always four substituents and is tetrahedral All (except proline) have an acidic carboxyl group, a basic amino group, and an alpha hydrogen connected to the α -carbon Each amino acid has an unique fourth substituent R In glycine, the fourth substituent is also hydrogen
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Natural Amino Acids L-stereochemistry How does biology select specifically L? A chemical synthesis will be a 50:50 mixture
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Stereochemistry Steve Castle – Mirror image of Morphine Tom Ganz – D-hepcidin
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Amino Acids: Classification Common amino acids can be placed in five basic groups depending on their R substituents: Nonpolar, aliphatic (7) Aromatic (3) Polar, uncharged (5) Positively charged (3) Negatively charged (2)
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Nonpolar, Aliphatic R Groups These amino acid side chains are hydrophobic
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Aromatic R Groups These amino acid side chains absorb UV light at 270-280 nm
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