18. Amino Acids and Proteins

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?

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.

Would you expect to find this segment at the center or at the surface of a protein? Why?

Consider the amino acids lysine, valine, and aspartate in an enzyme. State which of these amino acids have R groups that would:

b. be found in hydrophilic regions

Consider the amino acids lysine, valine, and aspartate in an enzyme. State which of these amino acids have R groups that would:

c. form hydrogen bonds

Consider the amino acids lysine, valine, and aspartate in an enzyme. State which of these amino acids have R groups that would:

d. form salt bridges

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

List the type of attractive force disrupted and the level of protein structure changed by the following denaturing treatments:

a. adding salt to soy milk to make tofu

Identify each of the following statements as characteristic of protein denaturation or protein hydrolysis. 

a. Milk curdles when lemon juice is added to it.