A new drug cleaves some amide linkages in a polypeptide chain. Which level of structure is directly affected?

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

Answer: (A)

Verified step by step guidance

1. Understand the levels of protein structure: Primary structure refers to the sequence of amino acids in a polypeptide chain. Secondary structure involves local folding into structures like alpha-helices and beta-sheets. Tertiary structure is the overall 3D shape of a single polypeptide chain. Quaternary structure involves the arrangement of multiple polypeptide chains.
2. Recognize that amide linkages, also known as peptide bonds, are the covalent bonds that connect amino acids in a polypeptide chain, forming the primary structure of proteins.
3. Identify that cleaving amide linkages directly affects the primary structure because it involves breaking the peptide bonds that hold the sequence of amino acids together.
4. Consider that changes in the primary structure can indirectly affect secondary, tertiary, and quaternary structures, as these higher levels of structure depend on the sequence and integrity of the primary structure.
5. Conclude that the direct effect of cleaving amide linkages is on the primary protein structure, as it disrupts the linear sequence of amino acids.