Transmembrane helices in proteins are predominantly composed of which type of amino acids?

Transmembrane helices in proteins are primarily composed of hydrophobic amino acids, which is why the correct answer pertains to this group. The structure of the cellular membrane is such that it is composed of a lipid bilayer, with the interior being hydrophobic due to the fatty acid tails of the phospholipids. As membranes are largely impermeable to polar or charged substances, the regions of proteins that span the membrane must also be hydrophobic to effectively interact with this environment.

Hydrophobic amino acids have nonpolar side chains that do not favorably interact with water, making them well-suited to reside within the lipid layers of the membrane. These amino acids often include residues such as leucine, isoleucine, valine, phenylalanine, and tryptophan, which facilitate proper folding and orientation of the protein within the membrane.

In contrast, charged, polar, or aromatic amino acids would have a tendency to interact with the aqueous environment, making them less favorable for integration into the hydrophobic core of the membrane. Thus, their presence in transmembrane helices is minimized, reinforcing the predominance of hydrophobic amino acids in this context.