So we have these two light chains that are bonded via disulfide bridges to these two heavy chains. And the two heavy chains are also bonded to each other by these disulfide bonds. Now, on every single antibody, we have a region known as the constant region and we have a region known as the variable region. Now, if we take a look at the following diagram of the antibody, these boxed in regions are the variable regions and the rest is the constant region. Now, what exactly is the variable region? Well, as the name applies, these variable regions actually contain specific types of sequences that can bind to that antigen.