Question

Write the structural features of an antibody molecule. Discuss any one mechanism by which antibodies interact with antigens.

Answer 1

Antibodies are immunoglobulins produced by B-lymphocytes and plasma cells. Antibody domains are compact structures bonded by a disulfide bond. Immunoglobulin monomers consist of two heavy (H chains) and two light (L chains) polypeptide chains linked by a disulfide bond. These chains have constant (C) and variable (V) sections. Papain cleaves the immunoglobulin molecule into two identical antigen-binding fragments - F_ab and F_c.

The active site of antibodies is the antigen-binding site of the Fab fragment of the immunoglobulin formed by the hypervariable regions of the H and L chains, which binds antigen epitopes. In the active center, there are specific complementary regions to specific antigenic epitopes. These epitopes interact with the antigen-binding site via multiple interactions including ionic, hydrophobic, hydrogen, dipole, etc. The affinity of the binding determines the specificity of the antibody molecule to the ceratin antigen type.