Which option lists the term describing the sequence of amino acids in a polypeptide?

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

Answer: (A)

The sequence of amino acids in a polypeptide is called the primary structure. This term refers to the linear order of amino acids linked by peptide bonds, which is the starting blueprint that determines how the chain can fold and function. The reason this is the right term is that the other levels describe how the polypeptide actually folds and assembles after the sequence is set: secondary structure involves local patterns like alpha helices and beta sheets formed by backbone hydrogen bonds; tertiary structure is the overall three-dimensional shape from interactions among side chains; quaternary structure is how multiple polypeptide chains come together. So the primary structure is specifically the exact amino acid sequence, the foundation for all higher-level structure.