PROTEINS Polymer of amino acids linked by amide linkage. Functions: 1. Nutritional: growth, digestion, metabolism (enzymes). 2. Physical structure: cheese, bread, foaming agent, gel￾forming.PROTEINS Polymer of amino acids linked by amide linkage. Functions: 1. Nutritional: growth, digestion, metabolism (enzymes). 2. Physical structure: cheese, bread, foaming agent, gel￾forming