Final answer:
All IgM antibodies have four constant domains in their heavy chain, which is typical of the IgM class and contributes to their classification and immunological functions. The Fc region is also common among all antibodies.
Step-by-step explanation:
All IgM antibodies have a common feature in their structure: they all contain four constant domains in their heavy chain. These constant domains are denoted as CH1, CH2, CH3, and C₄. The presence of these four constant domains is characteristic of IgM antibodies, which allows them to be classified within their specific immunoglobulin class. Meanwhile, the variable domain of the antibodies, which can be found in both the light and heavy chains, is responsible for the antigen-binding specificity. The constant domain, on the other hand, determines the antibody's class and its immunological functions.
The Fc region of an antibody, which is formed by the heavy chains coming together, is critical for the interaction with effector cells of the immune system through Fc receptors.