A paratope, also called an antigen-binding site, is a part of an antibody which recognizes and binds to an antigen. It is a small region (of 15 to 22 amino acids) of the antibody's Fv region, part of the fragment antigen-binding (Fab region), and contains parts of the antibody's heavy and light chains. Each arm of the Y shape of an antibody monomer is tipped with a paratope, which is a set of complementarity determining regions.
The part of the antigen to which the paratope binds is called an epitope. This can be mimicked by a mimotope. The figure given on the right hand side depicts the antibody commonly found on a B leukocyte. The engraved inner portions of idiotype (encircled region no.5) is the paratope where the epitope of the antigen binds.
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