 Pauling and Coray predicted a second type of secondary structure which they called beta sheets or generally they called that beta confirmations. This is a more extended confirmation of polypeptide chain as compared to alpha helix. So in this beta sheets the backbone of the polypeptide chain is extended into a zigzag structure. So a polypeptide chain that is arranged in a zigzag manner and the zigzag polypeptide chains are then arranged side by side. For example, one polypeptide chain that is zigzag and the other one is also zigzag and these two chains they are arranged side by side. So when they are arranged side by side they resemble a pleated sheet. That's why these structures were called as beta pleated sheets. So here you can see these three polypeptide chains 1, 2, 3 and these three chains are arranged in zigzag manner. And when these three chains zigzag chains they arrange each other side by side. They make a sheet and in this sheet these you can see these are the pleats. So this is called beta pleated sheet in which the chains are arranged side by side. In this sheet the R groups in the adjacent amino acids they protrude out from the sheet from the zigzag structure in the opposite directions. So if this is a polypeptide chain the R groups lie here, here and here. As you saw in case of alpha helix the R groups they lie outside the helix. So here too the R groups lie outside the sheet. This is because the R groups may not create any sort of hindrance. As you can see in this demonstration this is polypeptide chain which is zigzag arranged and the R groups they lie outside. They are actually protruding out of this sheet. And when another polypeptide chain will come to the side of this and like this they will also have their R groups protruding out. So these R groups will not create any hindrance in joining these polypeptide chains. Hydrogen bonds are formed between adjacent segments of polypeptide chains. So when two zigzag polypeptide chains come close to each other hydrogen bonds are formed between different segments of these two polypeptide chains. The adjacent polypeptide chains in a sheet can be either parallel or anti-parallel. So this arrangement of polypeptides is either parallel or anti-parallel. That is meant by parallel and anti-parallel. First let us see the arrangement of hydrogen bonds. So here you can see this is one polypeptide, this is another. They are arranged in a zigzag manner and the hydrogen bonds here you can see these are the hydrogen bonds. And these are present between the adjacent polypeptide chains. So this is anti-parallel polypeptide chain. Anti-parallel means at this corner you can see this is a minogroup and on the other chain here is a carbonyl group. If you see on the other side same one is a minogroup and the other one is carbonyl group. So the direction of these polypeptide chains is like this one is moving in this direction and the other one is moving in this direction. So this is called anti-parallel beta-plated sheet. If we see the parallel beta-plated sheet you can see a minogroup, both are on the same side. So the direction of these polypeptide chains is parallel. Look at the difference between the hydrogen bonding in anti-parallel and parallel beta-plated sheets. The hydrogen bonds are comparatively straight in case of anti-parallel beta-plated sheets while they are slightly distorted in case of parallel beta-plated sheets. That's why anti-parallel beta sheets are more stable as compared to parallel beta-plated sheets.