Final answer:
The word synonymous with 'aliphatic' in terms of amino acids is nonpolar. Nonpolar amino acids with aliphatic side chains have hydrophobic characteristics and play important roles in protein structure and function through hydrophobic interactions.
Step-by-step explanation:
In terms of amino acids, the word synonymous with 'aliphatic' is nonpolar. Aliphatic amino acids have 'R' groups that contain a chain of carbon atoms, and these chains are nonpolar in nature. Nonpolar amino acids, such as glycine, alanine, valine, leucine, and isoleucine, have hydrophobic side chains that do not interact with water.
In proteins, the nonpolar amino acids with aliphatic side chains are mainly involved in hydrophobic interactions. These interactions play a crucial role in protein structure and function, including protein folding and binding to other molecules.