What is the primary structure of a protein?

• A. Three-dimensional folding of the polypeptide chain
• B. Sequence of amino acids
• C. Arrangement of multiple polypeptide chains
• D. Order of nucleotides in the gene

Answer: (B)

The primary structure is the linear sequence of amino acids in a polypeptide, linked by peptide bonds. This one-dimensional order is the blueprint that determines how the chain will fold and interact, setting the stage for the secondary and tertiary (and possibly quaternary) structures that give a protein its final shape and function. The three-dimensional folding describes higher-level organization beyond the linear sequence, the arrangement of multiple polypeptide chains refers to quaternary structure, and the order of nucleotides in the gene is genetic information that encodes the amino acid sequence but is not the protein’s sequence itself.