Question

When the hydrophobic side chains of a protein in aqueous solution turn away from the protein's surface:

a. the protein undergoes denaturation

b. entropy is decreased

c. the protein is stabilized

d. hydrogen bonds are no longer possibe

Answer 1

Ans. Correct option. C. the protein is stabilized. The protein molecule is suspended in the aqueous environment of the cell. The exposure of hydrophobic residues on protein surface destabilize its structure because the polar aqueous environment repels the hydrophobic residues on protein. When the hydrophobic side chain is turned away from protein’s surface (say, buried towards the interior core of protein), the repulsion between the hydrophobic side chain and hydrophilic aqueous environment is minimized. Thus, the protein is better stabilized due to minimal repulsion between its surface and the aqueous environment.

# Option A. Incorrect. Protein denatures from hydrophobic side chains are exposed onto the protein surface because this exposure causes repulsion between hydrophilic aqueous environment and hydrophobic side chains.

# Option B. Incorrect. Entropy increases due to better solvation of the protein in the aqueous system when compared to the entropy of the system consisting of protein exposure hydrophobic residues on its surface in aqueous environment.

# Option D. Incorrect. Hydrogen bonds do NOT from between hydrophobic side chains and water in the surrounding. When hydrophobic side chains are turned away, the hydrophilic residues are exposed on protein surface simultaneously. So, overall, there shall be increase in number of H-bonds formed between protein surface and aqueous environment.