Announcements & Agenda (04/23/07)

1. Announcements& Agenda(04/23/07) • Pick Up Grade Sheets • Exam 3 back later this week • Class in VWF 102 on Wed! • Today • Amino acids (16.1-16.3) • Peptides (16.4) • Protein Structure (16.5)

2. I Thought Exam 3 was… • Piece of Cake • Easier than I Expected • Mostly What I Expected • Much Harder than I Expected • Uh Oh…

3. Ch 16: Amino Acids, Proteins, & Enzymes! Baaaaaa…….

4. Functions of Proteins Proteins perform many different functions in the body. Function of proteins determined by amino acids used and how they are put together in 2-D and 3-D

5. Proteins are made of Amino Acids 20 Amino acids • are the building blocks of proteins. • contain a carboxylic acid group and an amino group on the alpha () carbon. • are ionized in solution. • each contain a different side group (R). R side chain R │ + │ H2N—C —COOHH3N—C —COO− │ │ H H ionized form

6. “Essential” Amino Acids • must be obtained from the diet. • not synthesized by the body. • are in meat and diary products. • are missing (one or more) in grains and vegetables.

7. Types of Amino Acids Nonpolar Polar 4 main kinds: • nonpolar(hydrophobic) with hydrocarbon side chains. • polar (hydrophilic) with polar or ionic side chains. • acidic (hydrophilic) with acidic side chains. • basic (hydrophilic) with –NH2 side chains. Acidic Basic Be able to recognize these 4 kinds, no need to memorize all 20 for the Final Exam!!!!!!!!!!!!!!!!!

8. Nonpolar Amino Acids An amino acid is nonpolar when the R group is H, alkyl, or aromatic.

9. Polar Amino Acids An amino acid is polar when the R group is an alcohol, thiol, or amide.

10. Acidic & Basic Amino Acids An amino acid is • acidic when the R group is a carboxylic acid. • basic when the R group is an amine.

11. C O O H C O O H C O O H C O O H H N H H N H H N H H N H 2 2 2 2 C H C H C H S H C H S H 3 3 2 2 Fischer Projections of Amino Acids • are chiral except glycine • have Fischer projections that are stereoisomers. • ONLY “L” amino acids used in proteins. L-Alanine D-Alanine L-Cysteine D-Cysteine

12. Zwitterions A zwitterion • has charged−NH3+ and COO– groups. • forms when both the –NH2 and the –COOH groups in an amino acid ionize in water. • has equal + and – charges at the isoelectric point (pI). O O ║+║ NH2—CH2—C—OH H3N—CH2—C—O– glycine zwitterion of glycine

13. pH and ionization H+ OH– ++ H3N–CH2–COOHH3N–CH2–COO–H2N–CH2–COO– positive ion zwitterion negative ion low pH pI high pH

14. 16.4 Formation of Peptides

15. The Peptide Bond • is an amide bond. • forms between the carboxyl group of one amino acid and the amino group of the next amino acid. O CH3 O +||+| || H3N—CH2—C—O– + H3N—CH—C—O– O H CH3 O +|||| || H3N—CH2—C—N—CH—C—O– peptide bond

16. Formation of a Dipeptide

17. Naming Dipeptides (Tri… etc.)(NO NEED TO MEMORIZE NAMING RULES) A dipeptide • is named from the free amine (NH3+) using a -yl ending for the name. • names the last amino acid with the free carboxyl group (COO-) by its amino acid name.

18. Tour of Protein Structure…

19. Primary Structure of Proteins • sequence of amino acids • different proteins have different sequences • the backbone of a peptide chain or protein. Ala─Leu─Cys─Met

20. Oxytocin (pitocin) V. du Vigneaud • Nobel prize in chemistry 1955 • Uterine contracting and milk letdown hormone

21. Primary Structures • The nonapeptides oxytocin and vasopressin have similar primary structures. • Only the amino acids at positions 3 and 8 differ.

22. Primary Structure of Insulin Insulin • was the first protein to have its primary structure determined. • has a primary structure of two polypeptide chains linked by disulfide bonds. • has a chain A with 21 amino acids and a chain B with 30 amino acids.

23. Modification of insulin

24. Newer drugs for diabetics • http://www.rxlist.com/cgi/generic/byetta.htm • http://www.diabetesmonitor.com/symlin.htm • http://health.dailynewscentral.com/content/view/0002300/38/ • Glitazone http://www.gpnotebook.co.uk/cache/x20020419151758067650.htm

25. Insulin can be administered by… • Inhalation • Injection • oral

26. Secondary Structure Elements • a 3-D arrangement of amino acids in a polypeptide chain. • result from intermolecular forces such as hydrogen bonding • Several types of secondary structure • Alpha helices • Beta sheets • Triple helices

27. Beta Pleated Sheet • polypeptide chains side by side. • hydrogen bonds between chains. • has R groups above and below the sheet. • is typical of fibrous proteins such as silk.

28. Secondary Structure – Triple Helix The secondary structure of a triple helix is • three polypeptide chains woven together. • typical of collagen, connective tissue, skin, tendons, and cartilage.

29. Tertiary Structure • overall 3-D shape. • determined by attractions & repulsions between side chains of amino acids

30. Crosslinks in Tertiary Structures involve attractions and repulsions between the side chains of the amino acids in the polypeptide chain.

31. Quaternary Structure • combination of 2 or more protein units. • Example: hemoglobin consists of 4 subunits. • stabilized by the same interactions found in tertiary structures.

32. Summary of Protein Structure

33. Denaturation • the disruption of bonds in the secondary, tertiary and quaternary protein structures. • heat and organic compounds:break apart H bonds and disrupt hydrophobic interactions. • acids and bases:break H bonds between polar R groups and disrupt ionic bonds. • heavy metal ions:react with S-S bonds to form solids (among many other things) • agitationsuch as whipping that stretches peptide chains until bonds break.

34. Applications of Denaturation • cooking. • the skin is wiped with alcohol. • heat is used to cauterize blood vessels. • instruments are sterilized in autoclaves.