1. Chapter 19 Amino Acids and Proteins
19.1 Proteins and Amino Acids
Classify proteins by their functions in the body. Give the name
and abbreviation of an amino acid and draw its ionized structure.

2. Functions of Proteins
Function of protein p
Proteins perform many different functions in the body.

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)

4. Examples of Amino Acids

5. Types of Amino Acids Amino acids are classified as
nonpolar with hydrocarbon side chains (hydrophobic)
polar (neutral) with polar or ionic side chains (hydrophilic)
polar (acidic) with acidic side chains (hydrophilic)
polar (basic) with –NH2 side chains (hydrophilic)
Nonpolar Polar (neutral)
Acidic
Basic

6. Nonpolar Amino Acids
A nonpolar amino acid has an R group that is H, an alkyl group, or aromatic.

7. Polar (Neutral) Amino Acids
A polar amino acid has an R group that is an alcohol, thiol, or amide.

8. Polar (Acidic) and Polar (Basic) Amino Acids
An amino acid is
acidic with a carboxyl R group (COO–)
basic with an amino R group (NH3+)

9. Learning Check
Identify each of the following as a polar (P) or nonpolar (NP) amino acid.

10. Solution
Identify each of the following as a polar (P) or nonpolar (NP) amino acid.
Nonpolar (NP)
Polar (P)

11. Chapter 19 Amino Acids and Proteins
19.2 Amino Acids as Zwitterions
Draw the zwitterion of an amino acid at its isoelectric point and its ionized structure at pH values above or below its isoelectric point.

12. Zwitterions and Isoelectric Points
A zwitterion
has an equal number of —NH3+ and COO– groups
forms when the H from —COOH in an amino acid transfers to the —NH2

13. Isoelectric Point (pI)
The isoelectric points (pI)
are the pH at which zwitterions have an overall zero charge
of nonpolar and polar (neutral) amino acids exist at pH values from 5.1 to 6.3

14. Zwitterions in Acidic Solutions
In solutions that are more acidic than the pI,
the COO– in the zwitterion accepts a proton
the amino acid has a positive charge
Glycine, with a pI of 6.0, has a 1+ charge in solutions
that have a pH below pH 6.0.

15. Zwitterions in Basic Solutions
In solutions that are more basic than the pI,
the NH3+ in the zwitterion loses a proton
the amino acid has a negative charge
Glycine, with a pI of 6.0, has a 1– charge in solutions
that have a pH above pH 6.0.

16. pI, pH, and Charge

17. Summary of pH, pI, and Ionization

18. Ionized Forms of Polar (Acidic) and Polar (Basic) Amino Acids
also ionize the —COO and —NH3+ in their polar R groups
Zwitterions of polar (acidic) amino acids exist at pH values from 2.8 to 3.2.
Zwitterions of polar (basic) amino acids exist at pH values from 7.6 to 10.8.

19. Zwitterions of Aspartic Acid
Aspartic acid, a polar (acidic) amino acid,
has a pI of 2.8
forms a zwitterion at pH 2.8
forms negative ions with charges 1– and 2– at pH values greater than pH 2.8

20. 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 thin layer plate

21. Electrophoresis
With an electric current, a mixture of lysine, aspartate,
and valine are separated.

22. Electrophoresis
Used to screen for sickle cell trait in newborns

23. Learning Check Which structure represents:
A. alanine at a pH above its pI?
B. alanine at a pH below its pI?

24. Solution Which structure represents:
A. alanine at a pH above its pI? (2)
B. alanine at a pH below its pI? (1)

25. Chapter 19 Amino Acids and Proteins
19.3 Formation of Peptides
Draw the structure of a dipeptide.

26. 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
contains an N (free H3N+) terminal written on the left
contains a C (free COO –) terminal written on the right

27. Formation of a Dipeptide

28. Structure of protein p - 680
Naming Dipeptides
Structure of protein p
A dipeptide is named with
a yl ending for the N-terminal (free H3N+) amino acid
the full amino acid name of the free carboxyl group (COO–) at the C-terminal end

29. Learning Check
Draw the condensed structural formula, and give the name and abbreviation for the dipeptide Ser-Thr.

30. Solution

31. Chapter 19 Amino Acids and Proteins
19.4 Protein Structure: Primary and Secondary Levels
Describe the primary and secondary structures of a protein.

32. 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

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

34. Polypeptide in the body
H.N. P 684
Polypeptide in the body
The nonapeptides oxytocin and vasopressin
have similar primary structures
differ only in the amino acids at positions 3 and 8

35. Secondary Structure: Alpha Helix
The secondary structures of proteins indicate the
three-dimensional spatial arrangements of the
polypeptide chains.
An alpha helix (α-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 an —NH group and the O of C═O of the fourth amino acid down the chain

36. Secondary Structure: Alpha Helix (continued)

37. Secondary Structure: Beta-Pleated Sheet
A beta-pleated sheet (β-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

38. Secondary Structure: Beta-Pleated Sheet (continued)

39. Secondary Structure: Triple Helix
A triple helix
consists of three alpha helix chains woven together
contains large amounts of glycine, proline, hydroxyproline, and hydroxylysine that contain
–OH groups for hydrogen bonding
is found in collagen, connective tissue, skin, tendons, and cartilage
Primary & secondary Structure
p 684

40. Essential Amino Acids Essential amino acids
H.N. P 687
Essential amino acids
are the ten amino acids not synthesized by the body
must be obtained from the diet
are in meat and diary products
are missing (one or more) in grains and vegetables

41. Learning Check Indicate the type of protein structure as:
1) primary ) alpha helix
3) beta-pleated sheet ) 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

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

43. Chapter 19 Amino Acids and Proteins
19.5 Protein Structure: Tertiary and Quaternary Levels
Describe the tertiary and quaternary structures of a protein.

44. Tertiary Structure 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

45. Tertiary Structure (continued)
The interactions of the R groups give a protein its specific three-dimensional tertiary structure.

46. Cross-Links in Tertiary Structures

47. Globular Proteins Myoglobin Globular proteins
have compact, spherical shapes
carry out synthesis, transport, and metabolism in the cells
such as myoglobin store and transport oxygen in muscle

48. 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

49. Learning Check Select the type of tertiary interaction as:
1) disulfide 2) ionic
3) H bonds 4) hydrophobic
A. leucine and valine
B. two cysteines
C. aspartic acid and lysine
D. serine and threonine

50. Solution Select the type of tertiary interaction as:
1) disulfide 2) ionic
3) H bonds 4) hydrophobic
4 A. leucine and valine
1 B. two cysteines
2 C. aspartic acid and lysine
3 D. serine and threonine

51. Tertiary & Quaternary Structure of proteins p 687
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 with heme groups in each subunit that pick up oxygen for transport in the blood to the tissues
Hemoglobin

52. Hemoglobin & Myoglobin
Have similar biological functions.
Hemoglobin carry oxygen in blood while Myoglobin carry oxygen in muscle.
Myoglobin, a single polypeptide is identical to tertiary structure of each subunit of hemoglobin (4 units)
Myoglobin stores one oxygen whereas hemoglobin stores 4 oxygen.

53. Summary of Protein Structures (continued)

54. Summary of Protein Structures

55. Sickle – Cell Anemia
H.N. P 692
Caused by abnormality in the shape of one of the hemoglobin subunits. (β-chain)
The shape of RBC changed.
Less oxygen is transported.

56. Learning Check Identify the level of protein structure as:
1) primary 2) 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

57. Solution Identify the level of protein structure as:
1) primary 2) secondary
3) tertiary 4) quaternary
2 A. beta-pleated sheet
1 B. order of amino acids in a protein
4 C. a protein with two or more peptide chains
3 D. the shape of a globular protein
3 E. disulfide bonds between R groups

58. Chapter 19 Amino Acids and Proteins
19.6 Protein Hydrolysis and Denaturation
Describe the hydrolysis and denaturation of proteins.

59. Protein Hydrolysis 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

60. 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.

61. Denaturation 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

62. Applications of Denaturation
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
an autoclave

63. Learning Check
What are the products of the complete hydrolysis of the tripeptide Ala-Ser-Val?

64. Solution
What are the products of the complete hydrolysis of the tripeptide Ala-Ser-Val?
The products are the three amino acids: alanine, serine, and valine.

65. Learning Check
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?

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