Amino acids play central roles both as building blocks of proteins and as intermediates in metabolism. The 20 amino acids that are found within proteins convey a huge array of chemical versatility. Tertiary Structure of a Protein. The precise amino alkanoic acid content, and therefore the sequence of these amino acids, of a selected protein, is decided by the sequence of the bases in the gene that encodes that protein. The chemical properties of the amino acids of proteins determine the biological activity of the protein. Proteins not only Catalyze all (or most) of the reactions in living cells, they control virtually all cellular process. In addition, proteins contain within their amino acid sequences the necessary information to determine how that protein will fold into a three Dimensional structure, and the stability of the resulting structure. The field of folding and stability has been a critically important area of research for years, and remains today one among the good unsolved mysteries. It is, however, being actively investigated, and progress is being made a day.