Functional proteins are characterized not only by their amino acid sequence (primary structure) but also by their exact geometrical arrangement in space (called the secondary, tertiary, and quaternary structure). Most proteins contain one of both of the fundamental regular peptide backbone arrays, i.e. the a-helix or the b-sheet. These not only confer mech. stability on the protein but also protect active centers, create the correct microenvironment for the catalyzed reaction, or even participate in the catalytic process. Certain combinations of secondary superstructures are often found in proteins and control their structure and function. A brief discussion on protein structure detn. is provided.