Which amino acid is not typically involved in polar interactions?

Leucine is known for its hydrophobic properties due to its alkyl side chain, which is nonpolar. This characteristic means that leucine does not typically participate in polar interactions, as it lacks the functional groups necessary to engage in hydrogen bonding or other polar interactions commonly seen with amino acids such as serine, glutamine, and cysteine.

Serine and glutamine both contain hydroxyl and amide groups, respectively, allowing them to form hydrogen bonds with water or other polar molecules. Cysteine has a thiol group (–SH), which can also participate in polar interactions, particularly in forming disulfide bonds under oxidative conditions. In contrast, leucine’s hydrophobic nature makes it more likely to be found in the interior of proteins, away from the aqueous environment, further emphasizing its lack of involvement in polar interactions.