So we can have these two linear peptides or polypeptide chains basically point in the opposite directions or they can point in the same direction. So anti parallel directionality basically means they are stacked on top of one another, but they point in opposite directions. And the parallel data sheet basically means they're stacked on top of one another and they point in the same direction. So let's begin with the anti parallel case and let's discuss how the bonding actually takes place within the anti parallel beta pleated sheets. Now, because we essentially have one of these chains running in this direction and the other one is reversed, we see that these groups actually line up with one another perfectly. And what that means is if we examine this amino acid here and this amino acid here, their groups that are able to interact line up perfectly.