What type of interaction forms when two nonpolar side chains are in close proximity?
A hydrogen bond
B disulfide bridge
C hydrophobic interaction
D hydrophilic interaction
The correct answer and explanation is:
The correct answer is C) hydrophobic interaction.
Explanation:
Hydrophobic interactions are non-covalent interactions that occur when nonpolar molecules or side chains come together in an aqueous environment. These interactions are driven by the tendency of water molecules to exclude nonpolar substances due to the energetically unfavorable nature of water surrounding nonpolar groups. In other words, nonpolar side chains prefer to avoid interacting with water molecules, so they tend to cluster together, reducing their exposure to the surrounding water. This clustering or aggregation of nonpolar molecules is referred to as a hydrophobic interaction.
In the context of proteins, nonpolar side chains on the amino acids can form hydrophobic interactions when they are in close proximity. These interactions help stabilize the protein’s tertiary and quaternary structures. Since these side chains do not form hydrogen bonds or ionic bonds (which require partial charges or dipoles), hydrophobic interactions are essential in maintaining protein structure, especially in aqueous cellular environments.
The other answer choices are not correct for the following reasons:
- A) Hydrogen bond: This occurs between polar molecules or side chains that have partial positive and partial negative charges. Hydrogen bonds form between a hydrogen atom bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom. This is not the case with nonpolar side chains.
- B) Disulfide bridge: A disulfide bridge forms when two cysteine residues in a protein form a covalent bond between their sulfur atoms. This bond is specific to cysteine’s thiol group and does not occur between nonpolar side chains.
- D) Hydrophilic interaction: Hydrophilic interactions occur between polar or charged molecules that have an affinity for water. Nonpolar side chains do not exhibit hydrophilic properties and thus do not form hydrophilic interactions.
Hydrophobic interactions are critical in various biological processes, particularly in protein folding, membrane structure formation, and enzyme function.