Which of the following amino acid pairs are the most likely to form hydrogen bonds?

• A. Cysteine – cysteine
• B. Lysine – glutamate
• C. Serine – threonine
• D. Leucine – valine

Answer: (C)

Verified step by step guidance

1. Understand that hydrogen bonds are a type of weak interaction that occurs between a hydrogen atom covalently bonded to a more electronegative atom (like oxygen or nitrogen) and another electronegative atom with a lone pair of electrons.
2. Identify the functional groups present in each amino acid. Serine and threonine both contain hydroxyl (-OH) groups, which are capable of forming hydrogen bonds due to the presence of oxygen, a highly electronegative atom.
3. Consider the side chains of the amino acids: Serine has a -CH2OH group, and threonine has a -CH(OH)CH3 group. Both of these side chains contain hydroxyl groups that can participate in hydrogen bonding.
4. Compare with other pairs: Cysteine contains a thiol group (-SH), which is less effective at hydrogen bonding compared to hydroxyl groups. Lysine has an amino group, and glutamate has a carboxylate group, which can form ionic interactions but are less likely to form hydrogen bonds with each other. Leucine and valine have nonpolar side chains, which do not participate in hydrogen bonding.
5. Conclude that serine and threonine are the most likely to form hydrogen bonds due to the presence of hydroxyl groups in their side chains, which can interact with each other through hydrogen bonding.