1. 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

2. Chapter 242 Structure of Proteins =>

3. Chapter 243 Stereochemistry of  -Amino Acids =>

4. Chapter 244 Essential Amino Acids Arginine (Arg) Threonine (Thr) Lysine (Lys) Valine (Val) Phenylalanine (Phe) Tryptophan (Trp) Methionine (Met) Histidine (His) Leucine (Leu) Isoleucine (Ile) =>

5. Chapter 245 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. =>

6. Chapter 246 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. =>

7. Chapter 247 Zwitterion Amino acid exists as a dipolar ion. -COOH loses H +, -NH 2 gains H +. Actual structure depends on pH. =>

8. Chapter 248 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. pK a = 10 pK b = 12 =>

9. Chapter 249 Structure and pH =>

10. Chapter 2410 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. =>

11. Chapter 2411 Electrophoresis =>

12. Chapter 2412 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. =>

13. Chapter 2413 Structure of Peptide The peptide bond is an amide bond. Amides are very stable and neutral. =>

14. Chapter 2414 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. =>

15. Chapter 2415 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. =>

16. Chapter 2416 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. =>

17. Chapter 2417 Alpha Helix Each carbonyl oxygen can hydrogen bond with an N-H hydrogen on the next turn of the coil. =>

18. Chapter 2418 Pleated Sheet Each carbonyl oxygen hydrogen bonds with an N-H hydrogen on an adjacent peptide chain. =>

19. Chapter 2419 Summary of Structure =>

20. Chapter 2420 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.” =>

21. Chapter 2421

22. Chapter 2422 POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5 TH EDITION” L.G. WADE ALL MATERIALS USED WITH PERMISSION OF AUTHOR PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE ORGANIC CHEMISTRY COURSE BY: ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN