Antibodies are immunoglobulins(Igs) which are produced in the body in response to antigen or foreign bodies. Antibodies are produced by B lymphocytes and plasma cells. An antibody molecule consists of the following parts :

a) Heavy and light chains : An antibody molecule is made up of 4 peptide chains, two small called light chains and two longer called heavy chains. Antibody is thus represented as H2L2. The heavy chains have larger number of aminoacids while light chains have less aminoacids.

b) Constant and Variable regions : There are two different regions the constant and the variable region in each chain of the antibody.

c) Disulphide Bonds and Hinge region : A disulphide bond joins a light chain with a heavy chain. Two disulphide bond also link the two heavy chains. This part of the antibody displays considerable flexibility and is called hinge region.