What are the primary and secondary functions of proteins?

Proteins have a variety of primary functions, including serving as structural components (like collagen in connective tissues), enzymes that catalyze biochemical reactions, and transporters that move molecules across membranes. Secondary functions include roles in cell signaling, immune responses (as antibodies), and serving as hormones that regulate physiological processes. Additionally, proteins can also contribute to energy storage and muscle contraction. Their diverse functions stem from their unique amino acid sequences and complex three-dimensional structures.