The polypeptide starts at lower centre, runs up the left beta strand to the top left, back down the alpha helix and then up the second beta strand in the centre. This arranges the beta strands so that they run parallel. Beta sheet amino acids may be present but are randomly scattered throughout the sequence. The protein shown is myoglobin,depicted as a ribbon tracing the path of the polypeptide chain.
Alpha helix preferring amino acids are present, but scattered randomly throughout the sequence.
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.