18. Amino Acids and Proteins

Identify the level of protein structure associated with each of the following:

b. hydrogen bonding between backbone atoms

What level of protein structure is determined by the following:

a. Peptide bonds between amino acids?

What level of protein structure is determined by the following:

b. Hydrogen bonds between backbone carbonyl oxygen atoms and hydrogen atoms attached to backbone nitrogen atoms?

How do the following noncovalent interactions help to stabilize the tertiary and quaternary structure of a protein? Give an example of a pair of amino acids that could give rise to each interaction.

a. Hydrophobic interactions

Determine which of the following statements describes a tertiary structure of a protein.

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

______ a) Hydrophobic R groups seeking a nonpolar environment move toward the inside of the folded protein.  

______ b) Protein chains of collagen form a polypeptide chain composed of 3 alpha helices. 

______ c) An active protein contains 4 tertiary subunits. 

______ d) Two polypeptide chains held together by disulfide bridges. 

How do the following interactions help to stabilize the tertiary and quaternary structure of a protein? Give an example of a pair of amino acids that could give rise to each interaction.

b. Disulfide bonds

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?

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