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Immunoglobulin (Antibody) Structure

APBIO-2M0VDL

All immunoglobulins, regardless of their type (e.g., IgG, IgM, etc.) have a common structure. They are polypeptides (denoted by the amino and carboxyl ends) and resemble the letter "Y" (featured below).

By user:Y_tambe - Y_tambe's file, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1573513

Region 1 represents the "head region" (amino) of the antibody.

Region 2 represents the "tail region" (carboxyl) of the antibody.

Region 3 represents both heavy chains (light blue/dark blue/purple) with one variable and one constant domain (segment of the protein chain).

Region 4 represents the two (light-green/dark-green and light-green/blue ) light chains attached to the heavy chain with disulfide bonds. These chains also contain one variable and one constant domain (segment of the protein chain).

Region 5 represents the amino end of both light and heavy chains.

Region 6 represents the hinge region that connects either heavy chain in the middle of the protein.

Which of the following statements accurately describes the structure and/or function of the antibody (AKA immunoglobulin)?

A

The antigen is recognized by and attaches to Region 5 because the protein sequences in both heavy and light chains are unique for each antibody; therefore, it can attach to a wide range of potential antigens.

B

The antigen is recognized by and attaches to Region 2. This end of the antibody is ionic and adheres to all other ionic antigens.

C

The antigen is recognized by and attaches to Region 4 (only the light chains) whereas the heavy chain is only responsible for attaching the antibody to the B cell surface.

D

The antigen is recognized by and attaches to Region 6 because the hinge region can flex in order to adjust to a wide variety of potential antigens.