The IgG molecule is composed of four polypeptide chains: two identical chains with around 440 amino acid residues (heavy chains, H1 and H2) and two chains, also identical, with around 220 residues (light chains, L1 and L2). The heavy chains are glycoproteins, since they contain an oligosaccharide covalently bound to one of their asparagine residues.
Show each chain: H1 H2 L1 L2 as spacefill trace
As you see, folding of the chains creates several domains (regions with a three-dimensional structure compact and quite independent from the remainder of the molecule). You can appreciate that the structure of them all is very similar; later we will study its details. There are 3 globular domains, each one formed by two associated chains, and a connecting hinge region.
These domains are called Fab and Fc (the origin of these names is explained in the extension section). Fab, Fab, hinge, Fc