Structure is the result of two or more protein subunits assembling to form a larger, biologically active protein complex. 2. Structure is the sequence of amino acids in a protein. 3. Structure is achieved when a protein folds into a compact, three-dimensional shape stabilized by interactions between side-chain r groups of amino acids. 4. Structure describes the alpha-helices and beta-sheets that are formed by hydrogen bonding between backbone atoms located near each other in the polypeptide chain.