What term describes a chain of amino acids linked by peptide bonds, before it folds into higher-order structures?

• A. Primary structure
• B. Polypeptide
• C. Peptide
• D. Quaternary structure

Answer: (B)

A polypeptide. When amino acids join by peptide bonds, they form a linear polymer called a polypeptide. This is the chain that exists before any folding into higher-order shapes. The sequence of amino acids in this chain constitutes the primary structure, but the actual chain itself is the polypeptide. A peptide is generally a shorter chain, and quaternary structure describes how multiple polypeptides come together, which isn’t relevant to a single chain before folding.