Classify each of the following proteins according to its function:

a. hemoglobin, oxygen carrier in the blood

Classify each of the following proteins according to its function:

c. keratin, a protein found in hair

Classify each of the following proteins according to its function:

a. insulin, a protein needed for glucose utilization

Classify each of the following proteins according to its function:

c. casein, milk protein

How does the polarity of the R group in leucine compare to the R group in serine?

Draw the structure for each of the following amino acids at physiological pH:

a. lysine

Classify each of the amino acids in problem 16.5 as polar or nonpolar. If polar, indicate if the R group is neutral, acidic, or basic. Indicate if each is hydrophobic or hydrophilic.

Give the name for the amino acid represented by each of the following abbreviations:

d. Cys

Give the name for the amino acid represented by each of the following abbreviations:

d. G

Draw the condensed structural formula for each of the following peptides, and give its three-letter and one-letter abbreviations:

a. alanylcysteine

Draw the condensed structural formula for each of the following peptides, and give its three-letter and one-letter abbreviations:

c. glycylalanylvaline

Draw the condensed structural formula for each of the following peptides, and give its three-letter and one-letter abbreviations:

b. threonylleucine

Draw the condensed structural formula for each of the following peptides, and give its three-letter and one-letter abbreviations:

d. histidylglycylglutamylisoleucine

Peptides isolated from rapeseed that may lower blood pressure have the following sequence of amino acids. Draw the structure for each peptide and write the one-letter abbreviations.

a. Arg–Ile–Tyr

Peptides from sweet potato with antioxidant properties have the following sequence of amino acids. Draw the structure for each peptide and write the one-letter abbreviations.

b. Asn–Tyr–Asp–Glu–Tyr

Explain why each of the following pairs are complementary proteins:

a. beans and oats

What happens when a primary structure forms a secondary structure?

What is the difference in hydrogen bonding between an α helix and a β−pleated sheet?

What type of interaction would you expect between the R groups of the following amino acids in a tertiary structure?

c. serine and aspartate

What type of interaction would you expect between the R groups of the following amino acids in a quaternary structure?

a. phenylalanine and isoleucine

What type of interaction would you expect between the R groups of the following amino acids in a quaternary structure?

d. alanine and proline

A portion of a polypeptide chain contains the following sequence of amino acids:

—Leu—Val—Cys—Asp— 

a. Which amino acids are likely to be found on the inside of the protein structure? Why?

A portion of a polypeptide chain contains the following sequence of amino acids:

—Leu—Val—Cys—Asp—

c. How does the primary structure of a protein affect its tertiary structure?

In myoglobin, about one-half of the 153 amino acids have nonpolar R groups.

a. Where would you expect those amino acids to be located in the tertiary structure?

In myoglobin, about one-half of the 153 amino acids have nonpolar R groups.

b. Where would you expect the polar R groups to be in the tertiary structure?

Indicate whether each of the following statements describes primary, secondary, tertiary, or quaternary protein structure: 

c. Several polypeptides in a beta-pleated sheet are held together by hydrogen bonds between adjacent chains.

Indicate whether each of the following statements describes primary, secondary, tertiary, or quaternary protein structure:

b. Protein chains of collagen form a triple helix.

Indicate the changes in secondary and tertiary structural levels of proteins for each of the following:

b. Prior to giving an injection, the skin is wiped with an alcohol swab.

Indicate the changes in secondary and tertiary structural levels of proteins for each of the following:

c. To avoid spoilage, seeds are treated with a solution of HgCl₂.

Why do chemical reactions in the body require enzymes?