Secondary structure

Beta pleated sheet

In beta strand (or beta conformation), the polypeptide backbone is extended, rather than twisted onto itself in a helix. Observe its zig-zag arrangement.

It is common to find this conformation in several segments of the polypeptide chain, which align in parallel forming a beta sheet . Due to the zig-zag arrangement, it is also called a pleated sheet.

The backbone in a beta sheet is mostly planar , and from it protrude to both sides the sidechains of the amino acid residues .

Now let's display the peptide backbone using a fictitious line that joins the alpha carbons, and the sidechains using balls and sticks.

The beta sheets are stabilised by hydrogen bonds (----) between N and O belonging to the peptide bonds, as in alpha helix, but here they are interchain bonds, between the adjacent polypeptide chains: .

Finally, in large proteins beta strands are schematically rendered as a ribbon, that usually ends in an arrowhead to indicate the chain direction (from amino to carboxy termini): Show just the schematic rendering.