Which level of protein structure is most directly responsible for the specific shape and function of an enzyme?

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

Answer: (D)

Verified step by step guidance

1. Understand the levels of protein structure: Proteins have four levels of structure—primary, secondary, tertiary, and quaternary. Each level contributes to the overall shape and function of the protein.
2. Review the primary structure: The primary structure is the sequence of amino acids in a polypeptide chain, held together by peptide bonds. While it determines the basic composition, it does not directly dictate the enzyme's specific shape and function.
3. Examine the secondary structure: The secondary structure involves local folding of the polypeptide chain into alpha-helices and beta-pleated sheets, stabilized by hydrogen bonds. This contributes to the overall shape but is not the most direct determinant of the enzyme's specific function.
4. Focus on the tertiary structure: The tertiary structure is the three-dimensional folding of the polypeptide chain, driven by interactions such as hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges. This level of structure is most directly responsible for the enzyme's specific shape and function, including the formation of the active site.
5. Consider the quaternary structure: The quaternary structure involves the assembly of multiple polypeptide chains into a functional protein complex. While it is important for some enzymes, it is not the most direct determinant of the enzyme's specific shape and function compared to the tertiary structure.