Final answer:
A noncompetitive antagonist is a type of receptor antagonist that binds to a site on the receptor that is different from the active site and induces a conformational change in the receptor, preventing it from functioning properly.
Step-by-step explanation:
A noncompetitive antagonist is a type of receptor antagonist that binds to a site on the receptor that is different from the active site. This binding induces a conformational change in the receptor, preventing it from functioning properly. Unlike competitive antagonists, noncompetitive antagonists do not compete with the agonist for binding at the active site. Instead, they interfere with the receptor's ability to generate a response to the agonist.
For example, in the case of the neurotransmitter acetylcholine and its receptor, a noncompetitive antagonist may bind to an allosteric site on the receptor, causing a change in the receptor's shape that inhibits the binding of acetylcholine.
Noncompetitive antagonists are often irreversible, meaning that they form a covalent bond with the receptor and permanently inactivate it. This is in contrast to reversible antagonists, which can bind and unbind from the receptor.