Turns are marked in blue, and loop or random coil in white. The parallel beta sheet typically has non polar amino acids on both sides. If all the alpha helices line up on one side of the beta sheet, the beta sheet wraps around to form a parallel beta barrel with alpha helix on the outside. The parallel beta barrel at the core of triose phosphate isomerase. All the arrows run in the same direction.
Arrow heads point towards the carboxylate end of each strand.
A view of the parallel beta barrel component of triose phosphate isomerase from above. All side chain atoms are drawn in yellow. Note how the entire central region of the molecule is filled. Although this protein looks like a donut with a hole in the middle, the hole is fully packed with side chains. A cutaway view of triose phosphate isomerase, seen from above, including the beta barrel core and the alpha helix layer around the outside.