Nucleus of a cell: the largest organelle. Surrounded by a double membrane called the nuclear envelope consisting of nuclear pores. These pores regulate what goes in and out of the nucleus. A bulk of the interior of the nucleus is made up of nucleoplasm which contains chromatin and nucleoli.
A receptor antagonist is a type of receptor ligand or drug that blocks or dampens agonist-mediated responses rather than provoking a biological response itself upon binding to a receptor.They are sometimes called blockers; examples include alpha blockers, beta blockers, and calcium channel blockers.n antagonist that binds to the active site of a receptor is said to be non-competitive if the bond between the active site and the antagonist is irreversible or nearly so.
An opioid antagonist is a drug that binds itself to receptors in the brain and blocks the ability of the brain to respond to opiate use. Some drugs used are partial antagonists, while others provide full antagonist effects. An opioid antagonist is often used to combat addiction to opiates.