This page contains the pdb files referred to in the notes on beta sheets which you can use to help you understand beta sheet structure. Please use Jmol to view, and manipulate, these images.
Note the 'pleated' structure of the polypeptide backbone, alternate side chains pointing in the opposite direction (side chains are shown 'above' and 'below' the plane of the sheet in Figures 2.2 and 2.3), and the 'helix-like' structure of the strand where the strand is a 'helix' with n=2. The file is: beta strand
Figure 2.5 Beta sheets in OmpF (Outer membrane protein F)
Use Jmol to manipulate the protein and isolate the beta sheet. The pdb data file is 2omf.pdb by S.W.Cowan