Which class of antibody is characterized by having "y" chains?

The class of antibody characterized by having "y" chains is IgG. This class of immunoglobulin is known for its monomeric structure, consisting of two heavy chains and two light chains, which together form a Y-shaped molecule. The Y structure allows for effective binding to antigens, enhancing both the neutralization of pathogens and the activation of the immune system.

IgG is the most abundant antibody in the serum and plays a crucial role in immune responses by opsonizing pathogens, activating complement, and facilitating antibody-dependent cellular cytotoxicity. Its ability to cross the placenta also provides passive immunity to the fetus.

In contrast, while IgE, IgA, and IgM are also important classes of antibodies, they each have distinct structures that do not fit the "y" chain characterization. IgE is typically associated with allergic responses, IgA exists mainly in a dimeric form in secretions, and IgM is usually found as a pentamer composed of five monomer units. Understanding the distinct structural features of these antibody classes is essential for appreciating their roles in the immune response.