Which pair of amino acids can form hydrogen bonds between their R groups?

• A. Serine and Threonine
• B. Leucine and Isoleucine
• C. Valine and Phenylalanine
• D. Alanine and Glycine

Answer: (A)

Verified step by step guidance

1. Step 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. In amino acids, hydrogen bonds can form between polar R groups containing electronegative atoms.
2. Step 2: Analyze the R groups of each amino acid pair provided. Serine and Threonine have hydroxyl (-OH) groups in their side chains, which are polar and capable of forming hydrogen bonds. Leucine, Isoleucine, Valine, Phenylalanine, Alanine, and Glycine have nonpolar or hydrophobic side chains, which do not favor hydrogen bonding.
3. Step 3: Compare the chemical structures of the amino acids. Serine has a hydroxymethyl group (-CH2OH) in its R group, and Threonine has a hydroxyl group attached to a methyl group (-CH(OH)CH3). These polar groups can interact via hydrogen bonding.
4. Step 4: Eliminate pairs with nonpolar R groups. Leucine and Isoleucine, Valine and Phenylalanine, and Alanine and Glycine all have nonpolar or hydrophobic side chains, which are not conducive to hydrogen bonding.
5. Step 5: Conclude that the pair of amino acids capable of forming hydrogen bonds between their R groups is Serine and Threonine, due to the presence of polar hydroxyl groups in their side chains.