What defines the primary structure of a protein?

The primary structure of a protein is defined by its amino acid sequence. This sequence is critical because it determines how the protein will fold into its secondary, tertiary, and quaternary structures, ultimately influencing the protein's function. Each protein consists of a unique sequence of amino acids linked by peptide bonds, and even a slight change in this sequence can significantly affect the protein's properties and activities.

While three-dimensional folding, the arrangement of α-helices and β-sheets, and interactions involving multiple polypeptide chains are important aspects of protein structure, they pertain to higher levels of structure that are built upon the primary sequence. Understanding the primary structure is essential for grasping the complexities of protein function and interactions in biological systems. Thus, the amino acid sequence forms the foundational blueprint from which all other structural and functional characteristics of the protein emerge.