1. 1 Chapter 19 Amino Acids and Proteins 19.1 Proteins and Amino Acids 19.2 Amino Acids as Acids and Bases Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

2. 2 Functions of Proteins  Proteins perform many different functions in the body. TABLE 19.1

3. 3 Amino Acids 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 R │ + │ H 2 N—C —COOH H 3 N—C —COO− │ │ H H ionized form

4. 4 Examples of Amino Acids H + │ H 3 N—C—COO− │ Hglycine CH 3 + │ H 3 N—C—COO− │ Halanine

5. 5 Types of Amino Acids Amino acids are classified as  Nonpolar (hydrophobic) with hydrocarbon side chains.  Polar (hydrophilic) with polar or ionic side chains.  Acidic (hydrophilic) with acidic side chains.  Basic (hydrophilic) with –NH 2 side chains. Nonpolar Polar Acidic Basic Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

6. 6 Nonpolar Amino Acids A nonpolar amino acid has  An R group that is H, an alkyl group, or aromatic. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

7. 7 Polar Amino Acids A polar amino acid has  An R group that is an alcohol, thiol, or amide. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

8. 8 Acidic and Basic Amino Acids An amino acid is  Acidic with a carboxyl R group (COO − ).  Basic with an amino R group (NH 3 + ). Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Basic Amino Acids

9. 9 Learning Check Identify each as (P) polar or (NP) nonpolar. + A. H 3 N–CH 2 –COO − (Glycine) CH 3 | CH–OH + │ B. H 3 N–CH–COO − (Threonine)

10. 10 Solution Identify each as (P) polar or (NP) nonpolar. + A. H 3 N–CH 2 –COO − (Glycine) (NP) nonpolar CH 3 | CH–OH + │ B. H 3 N–CH–COO − (Threonine) (P) polar

11. 11 Fischer Projections of Amino Acids Amino acids  Are chiral except for glycine.  Have Fischer projections that are stereoisomers.  That are L are used in proteins. L -alanine D -alanine L -cysteine D -cysteine

12. 12 A zwitterion Has charged —NH 3 + and COO - groups. Forms when both the —NH 2 and the —COOH groups in an amino acid ionize in water. Has equal + and − charges at the isoelectric point (pI). O O ║ + ║ NH 2 —CH 2 —C—OH H 3 N—CH 2 —C—O – Glycine Zwitterion of glycine Zwitterions and Isoelectric Points

13. 13 In solutions more basic than the pI,  The —NH 3 + in the amino acid donates a proton. + OH – H 3 N—CH 2 —COO – H 2 N—CH 2 —COO – ZwitterionNegative ion at pI pH > pI Charge: 0Charge: 1 − Amino Acids as Acids

14. 14 In solutions more acidic than the pI,  The COO − in the amino acid accepts a proton. + H + + H 3 N—CH 2 —COO – H 3 N—CH 2 —COOH Zwitterion Positive ion at pI pH< pI Charge: 0Charge: 1+ Amino Acids as Bases

15. 15 pH and Ionization H + OH − + H 3 N–CH 2 –COOH H 3 N–CH 2 –COO – H 2 N–CH 2 –COO – positive ion zwitterion negative ion (at low pH) (at pI) (at high pH)

16. 16 Electrophoresis: Separation of Amino Acids In electrophoresis, an electric current is used to separate a mixture of amino acids, and  The positively charged amino acids move toward the negative electrode.  The negatively charged amino acids move toward the positive electrode.  An amino acid at its pI does not migrate.  The amino acids are identified as separate bands on the filter paper or thin­layer plate.

17. 17 Electrophoresis With an electric current, a mixture of lysine, aspartate, and valine are separated. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

18. 18 CH 3 CH 3 + | | H 3 N—CH—COOH H 2 N—CH—COO – (1)(2) Which structure represents: A. Alanine at a pH above its pI? B. Alanine at a pH below its pI? Learning Check

19. 19 CH 3 CH 3 + | | H 3 N—CH—COOH H 2 N—CH—COO – (1)(2) Which structure represents: A. Alanine at a pH above its pI? (2) B. Alanine at a pH below its pI? (1) Solution

20. 20 Chapter 19 Amino Acids and Proteins 19.3 Formation of Peptides Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

21. 21 The Peptide Bond A 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 CH 3 O + || + | || H 3 N—CH 2 —C—O– + H 3 N—CH—C—O– O H CH 3 O + || | | || H 3 N—CH 2 —C—N—CH—C—O– + H 2 O peptide bond

22. 22 Formation of A Dipeptide Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

23. 23 Learning Check Write the dipeptide Ser-Thr. OH CH 3 | | CH 2 O HCOH O + | ║ + | ║ H 3 N─CH─C─O – + H 3 N─CH─C─O – Ser Thr

24. 24 Solution Write the dipeptide Ser-Thr. OH CH 3 | | CH 2 O HCOH O + | ║ + | ║ H 3 N─CH─C─O – + H 3 N─CH─C─O – Ser peptide Thr OH bond CH 3 | | CH 2 OH HCOH O + | ║ | | ║ NH 3 ─CH─C─N ─CH─C─O – + H 2 O Ser-Thr

25. 25 Naming Dipeptides A dipeptide is named with  A -yl ending for the N-terminal amino acid.  The full amino acid name of the free carboxyl group (COO-) at the C-terminal end. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

26. 26 Write the three-letter abbreviations and names of the tripeptides that could form from two glycine and one alanine. Learning Check

27. 27 Write the names and three-letter abbreviations of the tripeptides that could form from two glycine and one alanine. Glycylglycylalanine Gly-Gly-Ala Glycylalanylglycine Gly-Ala-Gly Alanylglycylglycine Ala-Gly-Gly Solution

28. 28 Learning Check What are the possible tripeptides formed from one each of leucine, glycine, and alanine?

29. 29 Solution Tripeptides possible from one each of leucine, glycine, and alanine Leu-Gly-Ala Leu-Ala-Gly Ala-Leu-Gly Ala-Gly-Leu Gly-Ala-Leu Gly-Leu-Ala

30. 30 Learning Check Write the three-letter abbreviation and name for the following tetrapeptide: CH 3 │ CH 3 S │ │ CH – CH 3 SH CH 2 │ │ │ CH 3 O H CH 2 O H CH 2 O H CH 2 O + │ ║ │ │ ║ │ │ ║ │ │ ║ H 3 N – CH–C–N–CH–C–N–CH–C–N–CH–CO –

31. 31 Solution Ala-Leu-Cys-MetAlanylleucylcysteylmethionine CH 3 │ CH 3 S │ │ CH – CH 3 SH CH 2 │ │ │ CH 3 O H CH O H CH 2 O H CH 2 O + │ ║ │ │ ║ │ │ ║ │ │ ║ H 3 N – CH–C–N–CH–C–N–CH–C–N–CH–CO – AlaLeuCys Met

32. 32 Chapter 19 Amino Acids and Proteins 19.4 Protein Structure: Primary and Secondary Levels Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

33. 33 Primary Structure of Proteins The primary structure of a protein is  The particular sequence of amino acids.  The backbone of a peptide chain or protein. Ala─Leu ─ Cys ─ Met Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

34. 34 Primary Structures The nonapeptides oxytocin and vasopressin  Have similar primary structures.  Differ only in the amino acids at positions 3 and 8. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

35. 35 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. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

36. 36 Secondary Structure – Alpha Helix The secondary structures of proteins indicate the three-dimensional spatial arrangements of the polypeptide chains. An alpha helix has  A coiled shape held in place by hydrogen bonds between the amide groups and the carbonyl groups of the amino acids along the chain.  Hydrogen bonds between the H of a –N-H group and the O of C=O of the fourth amino acid down the chain.

37. 37 Secondary Structure – Alpha Helix Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

38. 38 Secondary Structure – Beta Pleated Sheet A beta-pleated sheet is a secondary structure that  Consists of polypeptide chains arranged side by side.  Has hydrogen bonds between chains.  Has R groups above and below the sheet.  Is typical of fibrous proteins such as silk.

39. 39 Secondary Structure: β-Pleated Sheet Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

40. 40 Secondary Structure: Triple Helix A triple helix  Consists of three alpha helix chains woven together.  Contains large amounts glycine, proline, hydroxy proline, and hydroxylysine that contain –OH groups for hydrogen bonding.  Is found in collagen, connective tissue, skin, tendons, and cartilage. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

41. 41 Indicate the type of protein structure as 1) primary 2) alpha helix 3) beta-pleated sheet 4) triple helix A. Polypeptide chains held side by side by H bonds. B. Sequence of amino acids in a polypeptide chain. C. Corkscrew shape with H bonds between amino acids. D. Three peptide chains woven like a rope. Learning Check

42. 42 Indicate the type of protein structure as: 1) primary 2) alpha helix 3) beta-pleated sheet 4) triple helix A. 3 Polypeptide chains held side by side by H bonds. B. 1 Sequence of amino acids in a polypeptide chain. C. 2 Corkscrew shape with H bonds between amino acids. D. 4 Three peptide chains woven like a rope. Solution

43. 43 Chapter 19 Amino Acids and Proteins 19.5 Protein Structure: Tertiary and Quaternary Levels Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

44. 44 Essential amino acids  Must be obtained from the diet.  Are the ten amino acids not synthesized by the body.  Are in meat and diary products.  Are missing (one or more) in grains and vegetables. Essential Amino Acids TABLE 19.3 Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

45. 45 The tertiary structure of a protein  Gives a specific three dimensional shape to the polypeptide chain.  Involves interactions and cross links between different parts of the peptide chain.  Is stabilized by Hydrophobic and hydrophilic interactions. Salt bridges. Hydrogen bonds. Disulfide bonds. Tertiary Structure

46. 46 Tertiary Structure  The interactions of the R groups give a protein its specific three- dimensional tertiary structure. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

47. 47 Tertiary Structure TABLE 19.5

48. 48 Globular Proteins Globular proteins  Have compact, spherical shapes.  Carry out synthesis, transport, and metabolism in the cells.  Such as myoglobin store and transport oxygen in muscle. Myoglobin Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

49. 49 Fibrous Proteins Fibrous proteins  Consist of long, fiber-like shapes.  Such as alpha keratins make up hair, wool, skin, and nails.  Such as feathers contain beta keratins with large amounts of beta-pleated sheet structures. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

50. 50 Select the type of tertiary interaction 1) disulfide2) ionic 3) H bonds4) hydrophobic A. Leucine and valine B. Two cysteines C. Aspartic acid and lysine D. Serine and threonine Learning Check

51. 51 Select the type of tertiary interaction as: 1) disulfide2) ionic 3) H bonds4) hydrophobic A.4 Leucine and valine B.1 Two cysteines C.2 Aspartic acid and lysine D. 3 Serine and threonine Solution

52. 52 Quaternary Structure The quaternary structure  Is the combination of two or more tertiary units.  Is stabilized by the same interactions found in tertiary structures.  Of hemoglobin consists of two alpha chains and two beta chains. The heme group in each subunit picks up oxygen for transport in the blood to the tissues. Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings hemoglobin

53. 53 Summary of Protein Structure TABLE 19.6 Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

54. 54 Summary of Protein Structures Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

55. 55 Identify the level of protein structure as: 1) Primary2) Secondary 3) Tertiary 4) Quaternary A. Beta-pleated sheet B. Order of amino acids in a protein C. A protein with two or more peptide chains D. The shape of a globular protein E. Disulfide bonds between R groups Learning Check

56. 56 Identify the level of protein structure 1. Primary2. Secondary 3. Tertiary 4. Quaternary A. 2 Beta-pleated sheet. B. 1 Order of amino acids in a protein. C. 4 A protein with two or more peptide chains. D. 3 The shape of a globular protein. E. 3 Disulfide bonds between R groups. Solution

57. 57 19.6 Protein Hydrolysis and Denaturation Chapter 19 Amino Acids and Proteins Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

58. 58 Protein hydrolysis  Splits the peptide bonds to give smaller peptides and amino acids.  Occurs in the digestion of proteins.  Occurs in cells when amino acids are needed to synthesize new proteins and repair tissues. Protein Hydrolysis

59. 59 Hydrolysis of a Dipeptide  In the lab, the hydrolysis of a peptide requires acid or base, water and heat.  In the body, enzymes catalyze the hydrolysis of proteins.

60. 60 Denaturation involves  The disruption of bonds in the secondary, tertiary and quaternary protein structures.  Heat and organic compounds that break apart H bonds and disrupt hydrophobic interactions.  Acids and bases that break H bonds between polar R groups and disrupt ionic bonds.  Heavy metal ions that react with S-S bonds to form solids.  Agitation such as whipping that stretches peptide chains until bonds break. Denaturation

61. 61 Denaturation of protein occurs when  An egg is cooked.  The skin is wiped with alcohol.  Heat is used to cauterize blood vessels.  Instruments are sterilized in autoclaves. Applications of Denaturation Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings

62. 62 What are the products of the complete hydrolysis of the peptide Ala-Ser-Val? Learning Check

63. 63 The products of the complete hydrolysis of the peptide Ala-Ser-Val are alanine serine valine Solution

64. 64 Tannic acid is used to form a scab on a burn. An egg is hard boiled by placing it in boiling water. What is similar about these two events? Learning Check

65. 65 Acid and heat cause the denaturation of protein. They both break bonds in the secondary and tertiary structures of proteins. Solution