Beta pleated sheet, illustration. This is a secondary structure formed from a protein's polypeptide chain of amino acids. This structure arises when two or more segments of the polypeptide line up next to each other and hydrogen bonds (white lines) form between the carbonyl group (a carbon atom double bonded to an oxygen atom) of one amino acid and the amino group (a nitrogen atom and two hydrogen atoms) of another. A complete beta pleated sheet is shown at left, the same beta pleated sheet without external side chain hydrogens is shown in the centre, and the same beta pleated sheet without any side chains (backbone only) is shown at right.