Which term describes the 3D shape of a polypeptide chain when it folds?

Which term describes the 3D shape of a polypeptide chain when it folds?

• A. Secondary structure
• B. Tertiary structure
• C. Quaternary structure
• D. Primary structure

Answer: (B)

The main concept here is how proteins are organized into structural levels, specifically the overall three-dimensional shape of a single folded polypeptide. When a polypeptide chain folds into its final 3D form, that arrangement is called its tertiary structure. This level results from interactions among the side chains and with the surrounding environment, including hydrophobic packing, hydrogen bonds, ionic interactions, disulfide bonds, and van der Waals forces, shaping the full 3D contour of one chain. Primary structure is simply the linear sequence of amino acids. Secondary structure refers to local patterns like alpha helices and beta sheets stabilized within the backbone. Quaternary structure describes how multiple polypeptide chains (subunits) come together to form a functional protein. So the folded single-chain 3D shape corresponds to tertiary structure, while quaternary structure would apply to proteins with more than one polypeptide chain. For example, myoglobin has a defined tertiary structure as a single chain, whereas hemoglobin exhibits quaternary structure due to its multiple subunits.

The main concept here is how proteins are organized into structural levels, specifically the overall three-dimensional shape of a single folded polypeptide. When a polypeptide chain folds into its final 3D form, that arrangement is called its tertiary structure. This level results from interactions among the side chains and with the surrounding environment, including hydrophobic packing, hydrogen bonds, ionic interactions, disulfide bonds, and van der Waals forces, shaping the full 3D contour of one chain.

Primary structure is simply the linear sequence of amino acids. Secondary structure refers to local patterns like alpha helices and beta sheets stabilized within the backbone. Quaternary structure describes how multiple polypeptide chains (subunits) come together to form a functional protein. So the folded single-chain 3D shape corresponds to tertiary structure, while quaternary structure would apply to proteins with more than one polypeptide chain. For example, myoglobin has a defined tertiary structure as a single chain, whereas hemoglobin exhibits quaternary structure due to its multiple subunits.