Final answer:
The primary structure of a protein is its sequence of amino acids. This sequence is vital as it determines the protein's higher-order structures and functionality. Secondary, tertiary, and quaternary structures are additional levels of organization within proteins.
Step-by-step explanation:
The primary structure of a protein refers to the sequence of amino acids in the protein. This sequence dictates how the protein will fold and function. Proteins can have secondary structures, like alpha helices and beta pleated sheets, which are formed by hydrogen bonds between amino acids. The tertiary structure is the overall 3D shape of the protein, which is critical to its function, resulting from a multitude of interactions within the protein. Finally, when more than one polypeptide chain interacts to form a complex, it is referred to as the quaternary structure, an example being hemoglobin which is comprised of four polypeptide subunits.