Final answer:
Proteins perform various functions such as acting as enzymes, providing structure, and transporting substances, but they do not serve as insulation; this role is typically associated with fats.
Step-by-step explanation:
Proteins serve multiple essential functions in the body, including acting as enzymes that speed up chemical reactions, providing structure for tissues and organs, and facilitating the transport of substances through the cell membrane. However, among the functions mentioned, the one that proteins do NOT perform is serving as insulation. While fats are commonly associated with insulating the body and maintaining body temperature, proteins do not have this role.
Roles of proteins include their function as structural components, such as collagen in connective tissues and keratin in skin, as well as contractile proteins like actin and myosin in muscles. Enzymes, a special class of proteins, are vital as they catalyze biochemical reactions, making processes such as digestion and metabolism efficient and possible. Proteins like hemoglobin are crucial for the transport of oxygen in the blood, and other proteins are involved in cell signaling and immune responses.