Video Transcript
The figure shows a drawing of the
bacterium Vibrio cholerae that causes cholera. Most of the symptoms of the disease
are caused by a toxin that it secretes. How do antibodies reduce the
symptoms of a cholera infection? (A) They bind to the toxin,
preventing it from causing its effects. (B) They hydrolyze the toxin
directly so that it is no longer active. (C) They enable the kidneys to
excrete the toxin in the urine. (D) They trigger a chemical attack
by natural killer cells. Or (E) they raise body temperature,
leading to toxin denaturation.
To answer this question, let’s
first remove the answer choices so we have more room to work with.
This question is asking us about
the bacterium that causes cholera and how antibodies can reduce its symptoms. In order to answer this question,
let’s first review the structure and function of an antibody. Antibodies are produced by
activated and differentiated B cells, which are part of the adaptive immune
system. They are usually depicted as
Y-shaped molecules with each tip of the Y exhibiting a specific antigen binding
site. An antigen refers to a foreign
substance or toxin that antibodies recognize and bind to.
In the case of cholera, the disease
is caused by a toxin secreted by the bacterium. The adaptive immune system is able
to produce B cells and antibodies that are specific for this toxin. Once the antibody binds to the
toxin, it can no longer cause its effects. Therefore, antibodies reduce the
symptoms of a cholera infection by binding to the toxin, preventing it from causing
its effects.
