The correct answer is - Primary structure.
Proteins are macromolecules made of amino acids. Thus, amino acids are units of a protein. The simplest level of protein structure is the primary structure. In primary structure, amino acids are linked in a sequence by peptide bonds. The amino group of one amino acid and the carboxyl group of another amino acid is linked to form a dipeptide and many amino acids linked in a sequence to form polypeptide, the primary structure of a protein.
