Beta pleated sheet

Beta pleated sheet is an example of the secondary structure of a protein.  The beta sheet is composed of beta strands which are polypeptides which are linked by hydrogen bonding .  Beta strands have a 2 residues repeat and when the polypeptide is fully extended it has 3.5 A is the distance between adjacent amino acids. The side chains of  adjacent amino acids point in opposite directions which respect to each other. Valine, threonine, histidine, tyrosine and isoleucine are most likely to found in beta sheets.   Whereas leucine, glutamate and alanine tend to be present in alpha helices. 

Beta sheets come in two form; anti-parallel and parallel. In anti-parallel the adjacent beta strands run in opposite direction, hydrogen bonding occurs between the NH group of one beta strand the C) group of the adjacent strand. This forms regular straight bonds. The parallel beta sheet consists of the both strands running in the same direction. The NH group hydrogen bonds to the CO group on the partner strand, but he CO group hydrogen bonds to the NH group on the adjacent strand two amino acids residues farther along the chain. . 

Beta sheets can be parallel or antiparallel or be mixture of the two .