Question

Explain the structure of a typical antibody molecule.

Answer 1

Structure of an Antibody (Gk. anri-against, body-body) Antibody is a glycoprotein, called immunoglobulin, that has a specific amino acid sequence by which it can interact with specific antigens. Antibodies form 20% of the plasma proteins. Each antibody has a combination of at least 2 light (L) and 2 heavy (H) polypeptide chains. The heavy chains have a larger number of amino acids, while the lighter chain has a smaller number of them. Usually, the polypeptides form a Y-shaped configuration. The stem of Y is exclusively formed by heavy chains. In the arms of Y, both light and heavy chains occur parallel to each other except for antigen-binding sites. Attachments and bendings occur by means of disulphide bonds (S-S). In certain immunoglobulins, the number of chain pairs can be JO. An antibody has a variable portion in the arms. It is called V-region or antigen-binding fragment, Fab. The remainder of the antibody is called constant portion or crystalline fragment, Fc.

Most of the antibodies function as monomers. A few, such as IgA and IgM, can occur both as monomers and polymers.