Beta sheet (antiparallel) model.  Structure is derived from 1AXC (human PCNA), residues A158-Q184.  The sequence was converted to Gly-Ala24-Gly manually and with the assistance of PyMOL, then rendered in Chimera.  Includes backbone hydrogen bonds and side chains represented as sticks, as well as the "cardinal" backbone representation to more accurately follow the atoms in the backbone within the ribbon.  Prints especially well at 3X size, for use in the classroom to aid students in learning secondary structure relationships.