SAT Biology Subject Test Practice Questions

Answer: D, Winding and coiling of the polypeptide. The secondary structure is the general three-dimensional form of local segments of a polypeptide.

Key Takeaway: A protein has four levels of structure. The primary structure is the amino acid sequence of the protein. The secondary structure is the general organization of the protein in space. The tertiary structure defines the exact atomic positions of each constituent of the protein. The quaternary structure only exists in proteins that are comprised of multiple protein subunits, and it describes the arrangement of the multiple folded protein molecules in the complex. While hydrogen bonding is a key element in protein structure and stability, it does not describe the structure of the protein.