What is the structure of an antibody?

An antibody has a 3D, Y-shaped structure, with a vertical leg (the base of the antibody) and two arms that extend upward from the vertical base. Each antibody is composed of a total of 4 protein chains – 2 light chains that weigh approximately 25 kilodaltons (kDa) and 2 heavy chains that weigh approximately 50 kDa. The chains are arranged in a light-heavy-heavy-light structure. The tip of the antibody, which is the paratope or the antigen-binding site, consists of both light and heavy chain portions.