19 Questions
What is the defining characteristic of an inverse agonist?
It has a much stronger affinity for the Ri conformation than the Ra state, stabilizing the Ri-D complex
Which of the following is an example of an inverse agonist?
GABA-receptor effectors
What is the defining characteristic of a chemical antagonist?
It interacts directly with the drug being antagonized to remove it or prevent it from reaching its target
What is the defining characteristic of an allosteric antagonist?
It binds to a different binding site, causing a conformational change that prevents the agonist from binding
Which type of antagonist does not depend on interaction with agonist receptors?
Chemical antagonist
Which of the following is an example of a chemical antagonist?
Dimercaprol for lead poisoning
What is the effect of an inverse agonist on constitutive receptor activity?
It decreases constitutive activity
Which type of antagonist binds to a different receptor, producing an effect opposite to that of the drug it is antagonizing?
Inverse agonist
Which type of antagonist binds to a different binding site on the receptor, causing a conformational change that prevents the agonist from binding?
Allosteric antagonist
If a ligand has a much stronger affinity to the Ri conformation than Ra state and stabilizes a large fraction in the Ri-D complex, the ligand will reduce any constitutive activity thus resulting in effects opposite of the effects produced by the full agonist. This is an example of an ______________.
inverse agonist
GABA-receptor effectors (inhibitory) are an example of an ______________ binding to a different receptor producing an effect opposite to that produced by the drug it is antagonizing.
inverse agonist
Dimercaprol for lead poisoning is an example of a ______________ antagonist that interacts directly with the drug being antagonized to remove it or to prevent it from reaching its target.
chemical
Pralidoxime for organophosphate poisoning is an example of a ______________ antagonist that interacts directly with the drug being antagonized to remove it or to prevent it from reaching its target.
chemical
An allosteric antagonist binds to a different binding site that forms a conformational change in the receptor preventing the ______________ to bind.
agonist
An antagonist will bind to the agonist ligand to prevent it from binding to the receptor complex and be excreted through ______________.
urine
Histamine (bronchoconstriction) and Epinephrine (bronchodilation) exemplify an ______________ where one drug produces an effect opposite to that of the other drug it is antagonizing.
inverse agonist
Propranolol and Thyroid hormone in allergy - anaphylaxis shock - decrease in bp scenario demonstrate the effect of an ______________.
inverse agonist
Anaphylactic shock leads to a decrease in BP due to allergy, which is an effect of an ______________ on constitutive receptor activity.
inverse agonist
Allosteric antagonists bind to a different binding site on the receptor, causing a conformational change that prevents the ______________ from binding.
agonist
Study Notes
Receptor Physiology
- Receptors: Protein molecules embedded in the plasma membrane surface, receiving signals from outside the cell, and causing cellular/tissue response when bound to ligands.
Ligand-Receptor Complex
- Ligand: An ion or molecule that donates a pair of electrons to form a coordination complex, derived from the Latin word "ligare," meaning "to bind."
-
Types of Ligands:
- Endogenous (produced by the human body)
- Exogenous (foreign material, such as drugs)
- Xenobiotics (compounds not made by the body)
Intracellular Receptors
- Location: Found in the cytoplasm of the cell
-
Types:
- Tyrosine Kinase Receptor: Normally have large extracellular and intracellular domains, and when ligands bind to the extracellular domain, a signal is transferred through the membrane, activating the enzyme, leading to a response.
- G-Protein Linked Receptors: Binds with a ligand and activates a membrane protein called a G-protein, interacting with either an ion channel or an enzyme in the membrane.
G-Protein Receptors
-
Types:
- Gs Receptor: Stimulative G protein, activates the enzyme adenylyl cyclase.
- Gi Receptor: Inhibitory G protein, inhibits adenylyl cyclase, lowering the level of cAMP in the cell.
- G4 Receptor: Activates a class of phospholipase C (PLC) enzyme, producing two secondary messengers: diacylglycerol (DAG) and inositol triphosphate (IP3).
Forces Affecting Ligand-Receptor Binding
- Covalent Bond: Strong, irreversible, and extremely stable.
- Electrostatic Bond: Weaker than covalent bond, with variable interaction strength.
- Hydrophobic Interactions: Generally weak, but important, and significant in driving interactions between lipophilic compounds and the lipid component of biological membranes.
Ligand-Receptor Interactions
-
Types:
- Agonism: Drugs that occupy receptors and activate them.
- Antagonism: Drugs that occupy receptors but do not activate them.
Antagonists
-
Types:
- Competitive Antagonist: Shifts the response curve to the right, but the same maximal effect is reached, and effects can be overcome by adding more agonist.
- Non-Competitive Antagonist: Causes downward shift in the response curve, and effects cannot be overcome by adding more agonist.
- Physiological Antagonist: Produces an effect that is opposite to the agonist's effect.
- Chemical Antagonist: Interacts directly with the drug being antagonized to remove it or prevent it from reaching its target.
- Allosteric Antagonist: Binds to a different binding site, forming a conformational change in the receptor, preventing the agonist from binding.
Variations in Receptor Response
- Tolerance: Repeated exposure to a ligand can lead to decreased receptor response.
- Receptor Desensitization: Repeated exposure to a ligand can lead to a decrease in receptor response due to receptor conformational changes.
Test your knowledge on the concept of LUNA and how cells respond to hydrophobic ligand molecules. Learn about intracellular receptors and the role of ligands in cellular signaling.
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