Question: Receptors (proteins)

Answer: A specific protein in either the plasma membrane or the interior of a target ell that a chemical messenger binds with, thereby invoking a biologically relevant response in that cell.

Question: Signal Transduction

Answer: A sequence of events in the cell leading to the cell’s response to a messenger.

Question: Specificity

Answer: The ability of a receptor to bind only one type or a limited number of structurally related types of chemical messengers.

Question: Saturation

Answer: The degree to which receptors are occupied by messengers. If all are occupied, the receptors are fully ____; if half are occupied, the ____ is 50% and so on.

Question: Affinity

Answer: The strength with which a chemical messenger binds to its receptor.

Question: Competition

Answer: The ability of different molecules to compete with a ligand for binding to its receptor. Competitors generally are similar in structure to the natural ligand.

Question: Antagonist

Answer: A molecule that competes with a ligand for binding to its receptor but does not activate signaling normally associated with the natural ligand. Therefore, it prevents the actions of the natural ligand. Antihistamines are examples.

Question: Agonist

Answer: A chemical messenger that binds to a receptor and triggers the cell’s response; often refers to a drug that mimics a normal messenger’s action. Decongestants are an example.

Question: Signal Transduction Pathways

Answer: The diverse sequences of events that link receptor activation to cellular responses.

Question: steroid-hormone-receptor

Answer: Found on the plasma membrane, in the cytosol, and also in the nucleus of the target cell. They are generally intracellular receptors (typically cytoplasmic) and initiate signal transduction for steroid hormones which lead to changes in gene expression over a time period of hours to days.