Advanced Placement (AP) Biology Practice Exam

How can some proteins regain their original structure after denaturation?

1. By changing their amino acid sequence

2. By removing destabilizing conditions

3. By involving more peptide bonds

4. By binding with nucleic acids

The correct answer is: By removing destabilizing conditions

Proteins are composed of long chains of amino acids that fold into specific three-dimensional shapes, which are critical for their biological function. Denaturation refers to the process by which proteins lose their native structure due to the disruption of non-covalent interactions, such as hydrogen bonds and ionic bonds, typically caused by changes in temperature, pH, or other environmental factors. The correct answer highlights that proteins can regain their original structure by removing destabilizing conditions, such as returning to their optimal temperature or pH. This process is often facilitated by the inherent properties of the protein's amino acid sequence, which contains the information necessary for the protein to refold correctly. In favorable conditions, proteins can refold spontaneously, often using chaperone proteins that assist in proper folding. While altering the amino acid sequence or increasing peptide bonds could change the structure of a protein, these actions would not restore the original structure after denaturation. Moreover, binding with nucleic acids does not directly contribute to refolding the protein back to its original conformation. Thus, the ability to regain original structure is largely dependent on the removal of factors that caused the denaturation in the first place.