Final answer:
The figure represents the antibody structure with light and heavy chains, where the constant domains are linked to antibody class and immune function, and variable domains contribute to antigen specificity.
Step-by-step explanation:
In the figure labeled as Figure Q4-49, we can identify various parts of the antibody structure. The constant domain of the light chain (label A) is the part of the light chain that does not vary among different antibodies of the same isotype. The constant domain of the heavy chain (label B) consists of three or four domains (CH¹, CH², CH³ and C¹´) which determine the class of the antibody and its immune function. The antigen-binding site (label C) is formed by the interaction of variable domains from both the heavy and light chains and is where the antibody binds to a specific epitope on an antigen. The variable domain of the heavy chain (label D) and the variable domain of the light chain (label E) both contribute to the antigen-binding site and are responsible for the specificity of the antibody.