What type of R group interaction is the most likely between the alanine and isoleucine residues?

• A. Hydrogen bonding
• B. Hydrophobic interaction
• C. Disulfide bridge
• D. Salt bridge

Answer: (B)

Verified step by step guidance

1. Begin by identifying the side chains (R groups) of alanine and isoleucine. Alanine has a methyl group (CH₃) as its side chain, while isoleucine has a more complex aliphatic side chain (CH(CH₃)CH₂CH₃).
2. Consider the nature of these side chains. Both alanine and isoleucine have nonpolar, hydrophobic side chains. This means they are likely to interact through hydrophobic interactions rather than polar interactions like hydrogen bonding.
3. Hydrophobic interactions occur when nonpolar molecules or groups cluster together to minimize their exposure to water. This is a common interaction in proteins, especially in the interior of the protein structure where water is excluded.
4. Evaluate the other options: Hydrogen bonding typically involves polar groups with hydrogen atoms bonded to electronegative atoms like oxygen or nitrogen. Disulfide bridges involve the covalent bonding of sulfur atoms from cysteine residues, and salt bridges involve ionic interactions between charged groups. None of these are applicable to alanine and isoleucine.
5. Conclude that the most likely interaction between alanine and isoleucine residues is hydrophobic interaction due to their nonpolar side chains.