1. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 1 17.1 Functions of Proteins 17.2 Amino Acids 17.3 Amino Acids as Acids and Bases Chapter 17 Amino Acids and Proteins

2. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 2 Functions of Proteins Proteins perform many different functions.

3. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 3 Amino acids: Are the building blocks of proteins. Contain a carboxylic acid group and an amino group on the alpha (  ) carbon. Have different side groups R that give each amino acid unique characteristics. Rside chain | H 2 N—C —COOH General structure of an |  -amino acid H 17.3 Amino Acids

4. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 4 Nonpolar Amino Acids Amino acids are classified as nonpolar when the R groups are H, alkyl, or aromatic.

5. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 5 Polar Amino Acids Amino acids are classified as polar when the R groups are alcohols, thiols, or amides.

6. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 6 Acidic and Basic Amino Acids Amino acids are classified as acidic when the R group is a carboxylic acid. Amino acids are classified as basic when the R group is an amine.

7. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 7 17.2 Chiral Objects Chiral compounds have the same number of atoms arranged differently in space. A chiral carbon atom is bonded to four different groups. Your hands are chiral. Try to superimpose your thumbs, palms, back of hands, and little fingers.

8. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 8 Mirror Images The mirror images of chiral compounds cannot be superimposed. When the H and I atoms are aligned, the Cl and Br atoms are on opposite sides.

9. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 9 Achiral Structures are Superimposable When the mirror image of an achiral structure is rotated, the structure can be aligned with the initial structure. Thus this mirror image is superimposable.

10. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 10 Some Everyday Chiral and Achiral Objects

11. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 11 Learning Check Identify each as a chiral or achiral compound.

12. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 12 Solution Identify each as a chiral or achiral compound. Chiral Achiral Chiral

13. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 13 Both the –NH 2 and the –COOH groups in an amino acid undergo ionization in water. A zwitterion forms that has + and – charge. At the isoelectric point (pI), the + and – charges in the zwitterion are equal. + NH 2 —CH 2 —COOH H 3 N—CH 2 —COO – Glycine Zwitterion of glycine Zwitterions

14. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 14 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 Higher pH Amino Acids as Acids

15. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 15 In solution 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 Low pH Amino Acids as Bases

16. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 16 pH and Ionization Acidic amino acids such as aspartic acid have a second carboxyl group that can donate and accept protons. The pI for aspartic acid occurs at a pH of 2.8.

17. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 17 Electrophoresis Electrophoresis separates amino acids according to their isoelectric points. Electrophoresi The positively charged amino acids move towards the negative electrode. The negatively charged amino acids move toward the positive electrode. An amino acid at its pI will not migrate in either direction.

18. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 18 Separation of Amino Acids When electrophoresis is completed, the amino acids are identified as separate bands on the filter paper or thin layer plate.

19. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 19 CH 3 CH 3 + | | H 3 N—CH—COOH H 2 N—CH 2 —COO – (1) (2) Which structure represents: A. Alanine at a pH above its pI? B. Alanine at a pH below its pI? Learning Check

20. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 20 CH 3 CH 3 + | | H 3 N—CH—COOH H 2 N—CH 2 —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

21. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 21 The Peptide Bond A peptide bond is an amide bond between the carboxyl group of one amino acid and the amino group of the next amino acid.peptide bond O CH 3 O + || + | || H 3 N—CH 2 —C—OH + H 3 N—CH—C—O – O H CH 3 O + || | | || H 3 N—CH 2 —C—N—CH—C—O – peptide bond

22. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 22 A Dipeptide A peptide is named from the free amine (NH 3 + ) using -yl endings for the names of the amino acids. The last amino acid with the free carboxyl group (COO - ) uses its amino acid name.

23. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 23 Write the names and three-letter abbreviations of the amino acids in the tripeptides that could form from two glycine and one alanine. Learning Check

24. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 24 Write the names and three-letter abbreviations of the amino acids in the tripeptides that could form from two glycine and one alanine. Gly-Gly-Ala Glycylglycylalanine Gly-Ala-GlyGlycylalanylglycine Ala-Gly-GlyAlanylglycylglycine Solution

25. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 25 Write the name of the following tetrapeptide using amino acid names and three-letter abbreviations. Learning Check

26. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 26 Ala-Leu-Cys-Met Alanylleucylcysteinylmethionine Solution AlaLeuCys Met

27. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 27 A polypeptide containing 50 or more amino acids is called a protein. The primary structure of a protein is the sequence of amino acids in the peptide chain. Ala-Leu-Cys-Met 17.7 Primary Structure

28. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 28 Primary Structures The nonapeptides oxytocin and vasopressin have similar primary structures. Only the amino acids at positions 3 and 8 differ.

29. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 29 Insulin Insulin: Was the first protein to have its primary structure determined. determined. Of humans has a primary structure that is similar to the insulin of pigs and cows.

30. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 30 The secondary structures of proteins indicate the arrangement of the polypeptide chains in space.secondary structures of proteins The alpha helix is a three-dimensional arrangement of the polypeptide chain that gives a corkscrew shape like a coiled telephone cord. 17.9 Secondary Structure: Alpha Helix

31. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 31 Alpha Helix The coiled shape of the alpha helix is held in place by hydrogen bonds between the amide groups and the carbonyl groups of the amino acids along the chain.

32. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 32 Secondary Structure: Pleated Sheet The pleated sheet:pleated sheet Holds proteins in a parallel arrangement with hydrogen bonds. Has R groups that extend above and below the sheet. Is typical of fibrous proteins such as silk.

33. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 33 A triple helix:triple helix Consists of three alpha helix chains. 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. Secondary Structure: Triple Helix

34. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 34 Essential amino acids: Are the ten amino acids that are not synthesized by the body. Must be obtained from the diet. Essential Amino Acids

35. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 35 Essential amino acids Essential amino acids are: Found in milk and eggs (complete proteins). Not all found in grains and vegetablesgrains (incomplete proteins). Obtained by combining two or more vegetables that provide complementary proteins. Essential Amino AcidsAmino Acids

36. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 36 Indicate the type of 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

37. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 37 Indicate the type of 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

38. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 38 The tertiary structure:tertiary structure Gives a specific overall shape to a protein. 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 17.10 Tertiary Structure

39. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 39 Tertiary Structure

40. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 40 Tertiary Structure The interactions of the R groups give a protein its specific three- dimensional tertiary structure.

41. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 41 Globular Proteins Globular proteinsGlobular proteins: Have compact, spherical shapes. Carry out synthesis, transport, and metabolism in the cells. Such as myoglobin store and transport oxygen in muscle. Myoglobin

42. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 42 Fibrous Proteins Fibrous proteins: Consist of long, fiber-like shapes. Such as alpha keratins make up hair, wool, skin, and nails.hair Such as feathers contain beta keratins with large amounts of beta-pleated sheet structures.

43. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 43 Select the type of tertiary interaction as: 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

44. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 44 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

45. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 45 17.11 Quaternary Structure The quaternary structure contains two or more tertiary subunits. Hemoglobin contains two alpha chains and two beta chains. The heme group in each subunit picks up oxygen for transport in the blood to the tissues.

46. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 46 Summary of Structural Levels

47. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 47

48. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 48 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

49. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 49 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

50. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 50 Protein hydrolysisProtein hydrolysis: Splits the peptide bonds to give smaller peptides and amino acids. Occurs in the digestion of proteins.digestion of proteins Occurs in cells when amino acids are needed to synthesize new proteins and repair tissues.synthesize new proteins andrepair tissues 17.12 Chemical Properties of Proteins

51. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 51 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.

52. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 52 Denaturation involves the disruption of bonds in the secondary, tertiary and quaternary protein structures. Denaturation

53. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 53 Denaturation 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. Agitation such as whipping stretches chains until bonds break.

54. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 54 Denaturation of protein occurs when: An egg is cooked. The skin is wiped with alcohol. Heat is used to cauterize blood vessels.cauterize Instruments are sterilized in autoclaves. Applications of Denaturation

55. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 55 What are the products of the complete hydrolysis of the peptide Ala-Ser-Val? Learning Check

56. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 56 The products of the complete hydrolysis of the peptide Ala-Ser-Val are: alanine serine valine Solution

57. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 57 Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events? Learning check

58. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 58 Acid and heat cause the denaturation of protein. They both break bonds in the secondary and tertiary structures of protein. Solution

59. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 59 Chapter Summary 20 different amino acids occur in proteins. Amino acid side chains have acidic or basic functional groups, or neutral groups that are either polar or nonpolar. Each amino acid has a isoelectric point – the pH at which the numbers of positive and negative charges in a solution are equal. A molecule can be identified as a chiral molecule if it contains a carbon atom that has four different groups.

60. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 60 Chapter Summary Contd. Chiral molecules do not have a mirror plane. Mirror images of chiral molecules are non- superimposable. All amino acids except glycine have four different groups bonded to the  -carbon, as a result they are chiral. Proteins are polymer of amino acids (polypeptides). Primary structure of a protein is the sequence in which the amino acids are connected by peptide bonds.

61. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 61 Chapter Summary Contd. Primary structures are written with the amino terminal amino acid on the left and carboxyl terminal amino acid on the right. Noncovalent interactions between side chain groups determine the overall three dimensional shape of a protein molecule. Secondary structure of a protein is the regular repeating three dimensional structures held together by hydrogen bonding between the backbone atoms within a chain or in adjacent chain.

62. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 62 Chapter Summary Contd. Tertiary structure of a protein is the overall three dimensional shape of a folded protein. Quaternary structure of a protein is the structure that incorporates more than one peptide chain. The peptide bonds are broken by hydrolysis. Denaturation is the loss of overall structure while retaining its primary structure. Agents that can cause denaturation of protein includes heat, mechanical agitation, polar organic solvents, detergents, salts, etc.

63. Copyright © 1804 Pearson Education Inc., publishing as Benjamin Cummings. 63 End of Chapter 17