The order of amino acids is the structure of proteins. a. stereo b. quaternary c. tertiary d. primary e. secondary

There are 4 level of protein structure known as Primary, secondary, tertiary and Quaternary. Primary refers to the sequence of amino acids in a linear pattern. Secondary undergoes repetitive folding of the polypeptide. Tertiary structure refers to the 3D structure of protein and compact making it the overall folding of the protein. Quaternary Structure describes how the different sub-unit of polypeptide interact with each other to form a single protein. Thus, the answer to the question is letter D.