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CHE 242 Unit VIII The Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their Derivatives CHAPTER

CHE 242 Unit VIII The Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their Derivatives CHAPTER TWENTY-FOUR. Terrence P. Sherlock Burlington County College 2004. Structure of Proteins. =>. Stereochemistry of - Amino Acids. =>. Arginine (Arg) Threonine (Thr)

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CHE 242 Unit VIII The Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their Derivatives CHAPTER

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  1. CHE 242Unit VIIIThe Structure, Properties, Reactions and Mechanisms of Carboxylic Acids and Their DerivativesCHAPTER TWENTY-FOUR Terrence P. Sherlock Burlington County College 2004

  2. Structure of Proteins => Chapter 24

  3. Stereochemistry of-Amino Acids => Chapter 24

  4. Arginine (Arg) Threonine (Thr) Lysine (Lys) Valine (Val) Phenylalanine (Phe) Tryptophan (Trp) Methionine (Met) Histidine (His) Leucine (Leu) Isoleucine (Ile) => Essential Amino Acids Chapter 24

  5. Complete Proteins • Provide all the essential amino acids. • Examples: those in meat, fish, milk, eggs. • Plant proteins are generally incomplete. • Vegetarians should eat many different kinds of plants, or supplement diet with milk or eggs. => Chapter 24

  6. Rare Amino Acids • 4-Hydroxyproline, 5-hydroxylysine found in collagen. • D-Glutamic acid in cell walls of bacteria • D-Serine in earthworms • -Aminobutyric acid, a neurotransmitter • -Alanine, constituent of the vitamin pantothenic acid. => Chapter 24

  7. Zwitterion • Amino acid exists as a dipolar ion. • -COOH loses H+, -NH2 gains H+. • Actualstructure depends on pH. => Chapter 24

  8. pKb = 12 pKa = 10 => Properties of Amino Acids • High melting points, over 200C • More soluble in water than in ether. • Larger dipole moments than simple acids or simple amines. • Less acidic than most carboxylic acids, less basic than most amines. Chapter 24

  9. Structure and pH => Chapter 24

  10. Isoelectric Point • pH at which amino acids exist as the zwitterion (neutral). • Depends on structure of the side chain. • Acidic amino acids, isoelectric pH ~3. • Basic amino acids, isoelectric pH ~9. • Neutral amino acids, isoelectric pH is slightly acidic, 5-6. => Chapter 24

  11. Electrophoresis => Chapter 24

  12. Reaction with Ninhydrin • Used to visualize spots or bands of amino acids separated by chromatography or electrophoresis. • Deep purple color formed with traces of any amino acid. => Chapter 24

  13. => Structure of Peptide • The peptide bond is an amide bond. • Amides are very stable and neutral. Chapter 24

  14. Peptide Bond Formation • The amino group of one molecule condenses with the acid group of another. • Polypeptides usually have molecular weight less than 5000. • Protein molecular weight 6000-40,000,000. => Chapter 24

  15. Classification of Proteins • Simple: hydrolyze to amino acids only. • Conjugated: bonded to a nonprotein group, such as sugar, nucleic acid, or lipid. • Fibrous: long, stringy filaments, insoluble in water, function as structure. • Globular: folded into spherical shape, function as enzymes, hormones, or transport proteins. => Chapter 24

  16. Levels of Protein Structure • Primary: the sequence of the amino acids in the chain and the disulfide links. • Secondary: structure formed by hydrogen bonding. Examples are -helix and pleated sheet. • Tertiary: complete 3-D conformation. • Quaternary: association of two or more peptide chains to form protein. => Chapter 24

  17. => Alpha Helix Each carbonyl oxygen can hydrogen bond with an N-H hydrogen on the next turn of the coil. Chapter 24

  18. => Pleated Sheet Each carbonyl oxygen hydrogen bonds with an N-H hydrogen on an adjacent peptide chain. Chapter 24

  19. Summary of Structure => Chapter 24

  20. Denaturation • Disruption of the normal structure of a protein, such that it loses biological activity. • Usually caused by heat or changes in pH. • Usually irreversible. A cooked egg cannot be “uncooked.” => Chapter 24

  21. Chapter 24

  22. POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5TH EDITION”L.G. WADEALL MATERIALS USED WITH PERMISSION OF AUTHORPRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGEORGANIC CHEMISTRY COURSEBY:ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN Chapter 24

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