Question

which of the following is not true of antibodies?
a they have a constant region that binds to an antigen.
b they are a y - shaped protein molecule.
c there are five classes of antibodies.
d they may act by neutralization.
e they have a variable region that binds to an antigen.

Explanation:

To determine the incorrect statement about antibodies:

• Option B: Antibodies are Y - shaped protein molecules (immunoglobulins), so this is true.
• Option C: There are five main classes of antibodies (IgG, IgA, IgM, IgD, IgE), so this is true.
• Option D: Antibodies can act by neutralizing antigens (e.g., neutralizing toxins or viruses), so this is true.
• Option E: The variable region of an antibody is responsible for binding to the antigen, so this is true.
• Option A: The variable region, not the constant region, of an antibody binds to the antigen. The constant region is involved in other functions like activating the immune system. So this statement is not true.

Answer:

A. They have a constant region that binds to an antigen.