The portion of the
immunoglobulin or
antibody molecule which contains the binding site for
antigens. The exact sequence of
amino acids in the area varies widely from molecule to molecule to accommodate a wide variety of antigens which the body may encounter. There are two such regions on each molecule (individually called
Fab fragments or
F-ab fragments). The molecule is shaped like the letter Y and the F(ab)2 fragments are located on the upper halves of the two fork parts. (The rest of the molecule, the stem and the lower parts of the forks, are the
Fc fragment).
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.