These classes are described and illustrated below.
Class a is comprised of a bundle of a helices connected by loops on the surface of the proteins.
Structure of a class proteins. A. Diagram showing a helical pattern of this class. B. Example of the class, hemoglobin, PDB file 3hhb displayed using Rasmol, using ribbons display and group color. A. B. 3hhb 2. Class b is comprised of antiparallel b sheets, usually two sheets in close contact forming a sandwich.