Final answer:
The isotype of an antibody is determined by its heavy chain. There are five types of heavy chains that give rise to different classes of antibodies, such as IgG, IgA, IgM, IgE, and IgD. The light chains play a role in antigen-binding but do not confer the antibody's isotype.
Step-by-step explanation:
The isotype of an antibody, also known as its class, is determined by the type of heavy chain present in its structure. Antibodies are glycoproteins composed of two main types of polypeptide chains: heavy and light chains. A key aspect is that the light chains come in two forms, kappa and lambda, but they do not determine the antibody's class. In contrast, the heavy chain varies among different antibody classes and includes five (5) types designated as gamma (y), alpha (a), mu (μ), epsilon (ε), and delta (δ). Therefore, the specific heavy chain present in an antibody is what confers its isotype, leading to the different classes of antibodies, such as IgG, IgA, IgM, IgE, and IgD.
Furthermore, the heavy chains are responsible for the formation of the Fc region of the antibody, which is essential for binding to various effector cells in the immune system, enhancing the specificity of immune responses. The light chains, while they pair with heavy chains and contribute to the formation of the antigen-binding site, do not determine the antibody's isotype.