Antibody structure Antibodies minimally consist of four proteins Two long proteins heavy chains Two shorter proteins light chains Constant region of each protein is similar in all antibodies Variable region of each protein is diverse. Antigen binding sites are pockets where antigen is held. Idiotypes are sites in direct contact with antigen. The portion of the antigen contacting the antibody is called the epitope. Antibody structure • Antibodies minimally consist of four proteins • Two long proteins = heavy chains • Two shorter proteins = light chains • Constant region of each protein is similar in all antibodies. • Variable region of each protein is diverse. • Antigen binding sites are pockets where antigen is held. • Idiotypes are sites in direct contact with antigen. • The portion of the antigen contacting the antibody is called the epitope