Which of the following best reflects hydrogen bonding interactions between water and the peptide chain?

• A. Water molecules form hydrogen bonds with the carbonyl oxygen and amide hydrogen atoms of the peptide backbone.
• B. Water molecules interact only with the hydrophobic side chains of the peptide.
• C. Water molecules are excluded from the peptide surface due to hydrophobic interactions.
• D. Water molecules form ionic bonds with the peptide backbone.

Answer: (A)

Verified step by step guidance

1. Understand the concept of hydrogen bonding: Hydrogen bonds are weak interactions that occur between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom with a lone pair of electrons.
2. Analyze the peptide backbone: The peptide backbone consists of repeating units of carbonyl groups (C=O) and amide groups (N-H). Both the carbonyl oxygen and the amide hydrogen are capable of participating in hydrogen bonding due to their electronegative nature.
3. Consider the interaction of water molecules: Water molecules have a polar structure, with the oxygen atom being electronegative and the hydrogen atoms being partially positive. This allows water to form hydrogen bonds with the carbonyl oxygen and amide hydrogen atoms in the peptide backbone.
4. Evaluate the incorrect options: Hydrophobic side chains repel water, so water does not interact with them. Water molecules are not excluded from the peptide surface due to hydrophobic interactions; instead, they interact with polar regions. Ionic bonds involve full charges, which are not relevant to the peptide backbone's hydrogen bonding.
5. Conclude the correct answer: Water molecules form hydrogen bonds with the carbonyl oxygen and amide hydrogen atoms of the peptide backbone, as these are the regions capable of engaging in hydrogen bonding interactions.