Which amino acid is described as nonpolar in nature?

Valine is classified as a nonpolar amino acid due to its hydrophobic side chain. The side chain of valine contains branched hydrocarbon groups, which do not readily interact with water, hence demonstrating nonpolarity. Nonpolar amino acids tend to be found in the interior of proteins, away from the aqueous environment, helping to stabilize protein structure through hydrophobic interactions.

In contrast, the other amino acids listed have polar or charged side chains. Tyrosine has a hydroxyl group that makes it polar, allowing it to form hydrogen bonds. Serine also contains a polar hydroxymethyl group, while glutamine has an amide side chain that contributes to its polarity. These characteristics differentiate them from nonpolar valine, underscoring why valine stands out as a nonpolar amino acid.