Slide 1
Binding to a receptor does not always activate it
A receptor is a molecular receiving site. A substance can bind to it and activate signaling, or bind without producing that same response.
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Affinity describes how readily binding occurs; efficacy concerns the response a bound substance can produce. Strong binding and strong activation are different properties.
Slide 2
An agonist activates a receptor response
An agonist activates a receptor-associated response. Its effect depends on the receptor and the signaling machinery of the cell.
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An endogenous hormone or neurotransmitter can be an agonist, as can a medicine. The category describes an action at a target rather than whether a substance is natural or manufactured.
Slide 3
An antagonist reduces the agonist’s action
An antagonist reduces an agonist’s action without activating the receptor in the same way. Blocking can occur through different molecular arrangements.
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A competitive antagonist can occupy the same binding site as an agonist. Other forms of interference do not follow that exact competition, so the term antagonist covers more than one mechanism.
Slide 4
A partial agonist has a lower response ceiling
A partial agonist produces a smaller maximum response than a full agonist in the same system. More binding does not always remove that limit.
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When both compete for receptors, the partial agonist can reduce the response that a full agonist would otherwise produce. Its role depends on what other signaling is present.
Slide 5
The surrounding tissue shapes the medicine’s effects
A receptor-level label does not describe every effect of a medicine. Different tissues and targets can produce different consequences.
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Laboratory response curves help characterize a mechanism, but clinical benefit also depends on distribution, duration and unwanted effects. Molecular classification is a starting point for evaluation.
Sources
- Pharmacokinetics & Pharmacodynamics
Open RN, Nursing Pharmacology; NCBI Bookshelf
- Pharmacological Characterization of GPCR Agonists, Antagonists, Allosteric Modulators and Biased Ligands
Assay Guidance Manual; NCBI Bookshelf