Question

This is for an immunology course.

Thank you!

14) Draw the fundamental structure of an immunoglobulin. Label the parts and be sure to label: light chain, heavy chain, antigen binding site, Fc, Fab, domains, hinge region, disulfide bonds, and variable region. With respect to antibody, what are allotype,

Answer 1

Structure of antibodies:

Antibodies are the “Y shaped” protienious structures (immunoglobulins) secreted by “plasma cells” (differentiated form of B cells and T cells). The different types of antibodies present in our body are, IgA, IgD, IgE, IgG and IgM. Among these, an IgG antibody provides resistance against a wide range of viruses and bacteria, and they make up about 80% of our antibody count.

The structure of antibody contains two polypeptide chains arranged in parallel; they are “one heavy chain and one light chain.” The two identical heavy chains are attached together by disulfide bonds, and form the base of the antibody. Similarly, the light chain and heavy chain are also attached together by disulfide bonds in both the halves of antibody molecule.

Both heavy chain and light chain contains “constant segments and variable segments.” Variable segment is present towards the free tip of the antibody; these free tips of two variable segments form the “antigen binding sites.” The antigen binding sites of antibodies bind to “antigenic determinant sites” of specific antigens (antigen-antibody complex) and inactivate them or stimulate the release of other molecules involved in immune response.

The variable regions show most diversity of pathogenic recognition sequences, because each antibody specifically binds to a specific antigen. The variable regions and constant regions have a specific region called “complementary determining regions.”

The amino acid sequences of these complementary determining regions (CDRs) (antigen-binding sites) are highly variable, for each group of antibodies. These CDRs are also called hyper variable regions.

The variable (V) type immunoglobulin regions have the CDRs on the V_L and V_H chains, namely CDR1, CDR2, and CDR3. Within the CDRs, a small number of amino acids show high diversity and specificity and they are called Framework regions. The constant (C) immunoglobulin regions differ from the variable (V) type immunoglobulin regions, based on the amino acid sequences or Framework regions. The difference in the amino acids is due to the mutations or recombination processes.

Antigen-binding site Antigen-binding site Heavy chain (H) LVariable CH1 regions (V) Light chain (L) Hinge region S-S S-S CH2 CH2 Constant regions (C) Interchain CH3 disulfide bonds CH3 STRUCTURE OF AN ANTIBODY