Which parts of an antibody molecule are different for IgG anitbody than IgM that attacks the same antigen?

The variable regions of the light and heavy chains are different between IgG and IgM antibodies that target the same antigen. These variable regions are responsible for binding to the antigen, and the differences in their amino acid sequences allow each type of antibody to bind to a different epitope on the antigen.

In addition, the constant regions of the heavy chains are different between IgG and IgM antibodies. These constant regions are responsible for the effector functions of antibodies, such as binding to complement proteins or Fc receptors on immune cells. The differences in the constant regions of IgG and IgM antibodies allow them to have different effector functions.

For example, IgG antibodies can bind to complement proteins and activate the complement cascade, which leads to the destruction of target cells. IgM antibodies cannot bind to complement proteins, but they can bind to Fc receptors on immune cells and activate them, leading to the release of inflammatory mediators.