What type of structure refers to the unique sequence of amino acids in a protein?

The primary structure of a protein refers to its unique sequence of amino acids, which are linked together by peptide bonds to form a long chain. This sequence is crucial because it ultimately determines the protein's shape and function. Each protein has a distinct sequence, dictated by the genetic code, and even a small change in this sequence can have significant effects on the protein's properties and its ability to perform its intended biological function. The primary structure, therefore, serves as the foundational layer upon which the other structural levels—secondary, tertiary, and quaternary—are built. These higher-order structures arise from interactions among the amino acids in the primary sequence but do not alter the sequence itself.