So these blue chains are connected, the purple chains by disulfide bonds. And these two heavy chains are connected to each other, but also by disulfide bonds as shown by these red bonds. Now, on that antibody we have a specific region known as the antigen binding side. And the antigen binding side contains a specific sequence of amino acids that has a high affinity for that antigen. Now, if these are the antigens, the antigens also contain a sequence of amino acids that basically bind to that antigen binding side of the antibody. So every antigen contains an epitope, which is a specific sequence of amino acids that binds onto the antigen binding side of that immunoglobulin of that antibody.