Structure of an antibody

An antibody molecule is comprised of four polypeptides; two identical heavy chains and two identical light chains connected by a disulfide bond.

An antibody molecule is Y-shaped, with two antigen binding sites at the tips of the Y. The light and heavy chains both contribute to the antigen binding sites. The areas on the antibody that recognize a unique antigen are called variable domains and are located at the amino-terminal end. The variable regions show considerable variation in the amino acid composition. The antibody base is composed of constant domains which are located at the carboxyl-terminal end.

The straight, lower half of an antibody is called the constant region which consists of two heavy chains. The two branches at the top are called the variable region consisting of two light chains. The chains are connected via disulphide bridges. At the tip of each branch is the antigen binding sites.

Figure 1: Antibody structure (simple)

The Y shape of an antibody can be divided into Fab and Fc regions. Fab regions contain the variable domain that binds to a specific antigen. The Fc regions contain a binding site for endogenous Fc receptors on the surface of lymphocytes, and is also the binding site for secondary antibodies.

Antibody

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Antibody structure variation and class

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Antibody