MP Board · Class 12 · Biology · Human Health and DiseasesDescribe the basic chemical structure of an antibody molecule with reference to its peptide chains and binding sites.

An antibody molecule consists of four polypeptide chains held together by disulfide bonds, which gives it a Y-shaped structure.

1. Peptide Chains: Out of the four chains, two are small and called light (L) chains, and two are longer and called heavy (H) chains. Hence, an antibody is represented as $H_2L_2$.
2. Variable and Constant Regions: Both light and heavy chains have a variable region at the N-terminal end and a constant region at the C-terminal end. The variable regions form the antigen-binding site.
3. Antigen-Binding Site (Paratope): Each antibody has two identical antigen-binding sites located at the tips of the 'Y' arms. These sites specifically recognize and bind to the epitopes on specific antigens, forming an antigen-antibody complex. \nDifferent classes of antibodies produced in the human body include IgA, IgM, IgE, and IgG.