Advanced Placement (AP) Biology Practice Exam

What causes denaturation of proteins?

1. Temperature changes only

2. Changes in pH, temperature, or salinity

3. Fluctuation of amino acid sequence

4. Presence of excessive amino acids

The correct answer is: Changes in pH, temperature, or salinity

Denaturation of proteins is primarily caused by changes in environmental conditions that disrupt the delicate interactions maintaining a protein's three-dimensional structure. Factors such as pH, temperature, or salinity play crucial roles in stabilizing the bonds and forces that hold a protein in its functional shape. When the temperature increases significantly, it can cause the protein’s thermal motion to become excessive, leading to the disruption of non-covalent interactions like hydrogen bonds and hydrophobic interactions, resulting in loss of structure and function. Similarly, alterations in pH can affect the charge properties of amino acid side chains, further disrupting ionic bonds and altering solubility. Changes in salinity can influence the ionic interactions between charged side chains, also contributing to denaturation. Thus, denaturation results from the interplay of these environmental factors, causing proteins to unfold and become non-functional, which is why the choice identifying changes in pH, temperature, or salinity accurately captures the causes of denaturation.