5.1 Receptors

Affinity

Strength with which ligand binds to its binding site

Agonists

Chemical messengers that bind to receptor and trigger cell’s response; often refer to drugs that mimic action of chemical normally in the body

Antagonist

Molecule that competes with another for a receptor and binds to the receptor but does not trigger the cell’s response

Antihistamine

Antagonists that block histamine from binding to its receptors on mast cells and triggering an allergic response

Beta-Andrenergic Receptor Blocker

Plasma membrane receptors for epinephrine and norepinephrine

Competition

Ability of similar molecules to combine with the same binding site or receptor

Down-Regulation

Decrease in number of target-cell receptors for a given messenger in response to a chronic high concentration of that messenger

Internalization

Down-regulation of plasma membrane receptors by receptor-mediated endocytosis

Oxymetazoline and Phenylephrine

Decongestant drugs that mimic the action of epinephrine on alpha-adrenergic receptors which result in the narrowing of blood vessels in the nose contract

Receptors

Protein either on cell surface, in the cytosol, or in the nucleus that binds a chemical messenger such as a hormone or neurotransmitter and mediates its actions

Saturation

Occupation of all available binding sites by their ligand

Signal Transduction

The process by which a messenger molecule initiates a sequence of intracellular events that leads to a cell’s response to that messenger

Specificity

Selectivity; ability of binding site to react with only one, or a limited number of, types of molecules

Up-Regulation

Increase in number of target-cell receptors for given messenger in response to chronic low extracellular concentration of that messenger