Which of the following is NOT a function of proteins?

The correct answer highlights that insulation is not a primary function of proteins. While proteins serve various essential roles in biological systems, including enzymatic activity, transport, and defense, insulation is primarily a function associated with lipids, such as fats and oils. Proteins are involved in catalyzing biochemical reactions (enzymatic activity), carrying molecules throughout the body (transport), and contributing to the immune response (defense). Insulation, on the other hand, is mainly achieved through adipose tissue, which is composed of lipid materials that help maintain body temperature and protect organs, rather than through protein structures. This distinction helps clarify the unique roles of different biomolecules in living organisms.