Question

Although all immunoglobulin molecules are constructed from a basic unit of 2 heavy chains and 2 light chains, multimers can also be formed. A separate polypeptide chain known as the J (joining) chain promotes polymerization by linking to the cysteines of heavy chains. The immunoglobulin isotypes that can form polymers are?

IgD and IgM
IgM and IgA
IgM and IgE
IgE and IgD
IgA and IgE

Answer 1

The immunoglobulin isotypes that can form polymers with the inclusion of the J chain are IgM and IgA. IgM forms a pentameric structure, while IgA can be found as a dimer in secretions. Other isotypes, such as IgG, IgE, and IgD, typically do not form multimers involving the J chain.

Step-by-step explanation:

The immunoglobulin isotypes that can form polymers and contain the J (joining) chain are IgM and IgA. The J chain promotes polymerization by linking the cysteine residues of the heavy chains in these multimers. IgM is typically a pentamer, where five immunoglobulin molecules are linked together by intermolecular disulfide bonds with a single J chain, making it the largest immunoglobulin molecule. On the other hand, IgA can exist as a monomer or as a dimer in secretions, also involving the J chain in its polymerized form. Other isotypes, like IgG, IgE, and IgD, do not typically form polymers and do not involve the J chain.

All immunoglobulin molecules are composed of 2 identical heavy chains and 2 identical light chains arranged in a 'Y' shape. The basic structure of these molecules is referred to as a monomer, which has a molecular weight of around 150,000 daltons. Variations in the heavy chain characterize different immunoglobulin isotypes, such as IgM (µ chain), IgA (α chain), IgG (γ chain), IgE (ε chain), and IgD (δ chain).