<P> There are five types of mammalian Ig heavy chain denoted by the Greek letters: α, δ, ε, γ, and μ . The type of heavy chain present defines the class of antibody; these chains are found in IgA, IgD, IgE, IgG, and IgM antibodies, respectively . Distinct heavy chains differ in size and composition; α and γ contain approximately 450 amino acids, whereas μ and ε have approximately 550 amino acids . </P> <Ol> <Li> Fab region </Li> <Li> Fc region </Li> <Li> Heavy chain (blue) with one variable (V) domain followed by a constant domain (C 1), a hinge region, and two more constant (C 2 and C 3) domains </Li> <Li> Light chain (green) with one variable (V) and one constant (C) domain </Li> <Li> Antigen binding site (paratope) </Li> <Li> Hinge regions </Li> </Ol> <Li> Heavy chain (blue) with one variable (V) domain followed by a constant domain (C 1), a hinge region, and two more constant (C 2 and C 3) domains </Li> <Li> Light chain (green) with one variable (V) and one constant (C) domain </Li>

What provides information about molecules on the cell surface