Light and heavy chains

Every  molecule  of  immunoglobulin G or IgG  is  Y-shaped  and  consists  of  four polypeptide  chains  connected  together  through disulfide  bonds;  two identical  copies  of light L chains about 220 amino acids long and two identical  copies of heavy H  chains  about  440  amino  acids  long.   The  N-terminal  ends  of one heavy  chain  and  its  neighboring   light  chain  cooperate   to  form  an  antigen binding site, so which the immunoglobulin G  molecule has two binding sites for antigen, which is, it is bivalent.  Since of this, a single antibody molecule can bind so cross-link and two antigen molecules and precipitate antigens out of solution.