Advanced Placement (AP) Biology Practice Exam

Which interaction is primarily involved in tertiary protein structure?

1. Hydrogen bonding

2. Ionic interactions

3. Hydrophobic interactions

4. All of the above

The correct answer is: All of the above

The tertiary structure of a protein refers to the overall three-dimensional shape formed by the folding of the polypeptide chain, which is crucial for the protein's function. This intricate shape is stabilized by various types of interactions between the side chains (R groups) of the amino acids. Hydrogen bonding plays a significant role in maintaining the tertiary structure as it occurs between polar side chains or between side chains and the backbone of the polypeptide. These bonds help to form and stabilize secondary structures, which can further influence the overall shape of the protein. Ionic interactions, also known as electrostatic interactions, occur between positively charged and negatively charged side chains (such as between lysine and aspartate). These interactions can help to reinforce the protein's structure by providing additional stability where charged residues come into close proximity. Hydrophobic interactions are critical in tertiary structure as well. Non-polar side chains tend to cluster together to avoid contact with water, driving the folding process toward a more energetically favorable configuration that minimizes exposure of these residues to the aqueous environment. Given that all three types of interactions - hydrogen bonds, ionic interactions, and hydrophobic interactions - contribute significantly to the stabilization of the tertiary structure, it is accurate to state that these interactions collectively are primarily