Receptor theories MCQs With Answer

Introduction: Receptor theories MCQs With Answer provide B. Pharm students a focused way to master pharmacodynamics concepts such as receptor theory, occupancy models, two‑state and rate theories, agonist and antagonist classifications, affinity, efficacy, potency, dose‑response relationships, spare receptors, allosteric modulation, Schild analysis, and signal transduction pathways. These targeted multiple‑choice questions reinforce key principles like Kd, Bmax, partial and inverse agonism, competitive versus noncompetitive antagonism, and mechanisms of desensitization and receptor regulation. Clear explanations with answers help consolidate understanding for exams and clinical application. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement best describes the occupancy theory of drug action?

• The magnitude of response is independent of receptor binding.
• Response is proportional to the number of occupied receptors.
• Only receptor desensitization determines response magnitude.
• Agonists and antagonists produce equal efficacy.

Correct Answer: Response is proportional to the number of occupied receptors.

Q2. What does the term “affinity” describe in receptor pharmacology?

• The maximal effect a drug can produce.
• The tendency of a drug to bind to its receptor.
• The speed at which a drug is metabolized.
• The ability of a bound drug to activate a receptor.

Correct Answer: The tendency of a drug to bind to its receptor.

Q3. How is “efficacy” defined for an agonist?

• The dose required to produce 50% of maximal effect.
• The capacity of a drug to bind its receptor tightly.
• The ability of an agonist to produce a maximal biological response.
• The duration of receptor occupancy.

Correct Answer: The ability of an agonist to produce a maximal biological response.

Q4. Which term best describes “potency” of a drug?

• The maximum response achievable with the drug.
• The concentration required to produce a defined fraction (e.g., 50%) of the maximal response.
• The fraction of receptors occupied at zero drug concentration.
• The inverse of intrinsic efficacy.

Correct Answer: The concentration required to produce a defined fraction (e.g., 50%) of the maximal response.

Q5. What is the equilibrium dissociation constant (Kd)?

• The dose that causes toxicity in 50% of subjects.
• The drug concentration at which 50% of receptors are occupied.
• The maximal number of binding sites in a tissue.
• The rate constant for receptor internalization.

Correct Answer: The drug concentration at which 50% of receptors are occupied.

Q6. What does Bmax represent in receptor binding studies?

• The concentration of ligand producing 50% effect.
• The total number of available receptor binding sites in a tissue.
• The binding affinity of a ligand for a receptor.
• The maximum intrinsic activity of an agonist.

Correct Answer: The total number of available receptor binding sites in a tissue.

Q7. How does a reversible competitive antagonist affect a graded dose‑response curve?

• It reduces the maximal response (Emax).
• It produces a leftward shift of the curve.
• It causes a parallel rightward shift without reducing Emax.
• It converts a full agonist into an inverse agonist.

Correct Answer: It causes a parallel rightward shift without reducing Emax.

Q8. Which effect is characteristic of a noncompetitive antagonist?

• Surmountable antagonism by increasing agonist concentration.
• Selective increase in potency without affecting Emax.
• Irreversible or functionally non‑surmountable reduction in Emax.
• Enhancement of agonist binding affinity at the orthosteric site.

Correct Answer: Irreversible or functionally non‑surmountable reduction in Emax.

Q9. What defines a partial agonist at a receptor?

• A ligand that produces no intrinsic activity but blocks agonists.
• A ligand that produces a submaximal response even when occupying all receptors.
• A ligand that irreversibly activates the receptor.
• A ligand that only binds allosteric sites.

Correct Answer: A ligand that produces a submaximal response even when occupying all receptors.

Q10. What is an inverse agonist?

• A drug that increases receptor expression on the membrane.
• An antagonist that blocks agonist binding without affecting basal activity.
• A ligand that decreases constitutive receptor activity below basal level.
• A ligand that only binds in the presence of the agonist.

Correct Answer: A ligand that decreases constitutive receptor activity below basal level.

Q11. What is meant by “spare receptors”?

• Extra receptors that do not bind ligand under any condition.
• The presence of more receptors than are required to produce a maximal response.
• Receptors only expressed during disease states.
• Receptors located exclusively inside the nucleus.

Correct Answer: The presence of more receptors than are required to produce a maximal response.

Q12. Schild analysis is used to determine which pharmacological parameter?

• The intrinsic efficacy of an agonist.
• The pA2 value of a competitive antagonist.
• The Bmax of a receptor preparation.
• The rate of receptor internalization.

Correct Answer: The pA2 value of a competitive antagonist.

Q13. The two‑state model of receptors proposes what concept?

• Receptors are either upregulated or downregulated only by gene expression.
• Receptors exist in equilibrium between active and inactive conformations.
• All agonists convert receptors irreversibly to an active state.
• Ligands bind only when receptors are phosphorylated.

Correct Answer: Receptors exist in equilibrium between active and inactive conformations.

Q14. Which mechanisms commonly underlie receptor desensitization?

• Increased agonist diffusion and enhanced binding affinity.
• Phosphorylation of the receptor, arrestin binding, and internalization.
• Permanent mutation of receptor genes within hours.
• Conversion of agonists into antagonists by metabolism.

Correct Answer: Phosphorylation of the receptor, arrestin binding, and internalization.

Q15. How do allosteric modulators act on receptors?

• They bind the orthosteric site and directly activate the receptor like full agonists.
• They bind a distinct site and modify the affinity or efficacy of orthosteric ligands.
• They irreversibly block receptor gene transcription.
• They only act by decreasing receptor density on the membrane.

Correct Answer: They bind a distinct site and modify the affinity or efficacy of orthosteric ligands.

Q16. What is the main difference between graded and quantal dose‑response curves?

• Graded curves measure all‑or‑none responses; quantal measure magnitude.
• Graded curves show population variability; quantal show single subject response.
• Graded curves depict continuous change in effect magnitude; quantal curves show the fraction of a population achieving a defined effect.
• There is no difference; both terms are interchangeable.

Correct Answer: Graded curves depict continuous change in effect magnitude; quantal curves show the fraction of a population achieving a defined effect.

Q17. ED50 is defined as:

• The dose that is lethal to 50% of subjects.
• The dose that produces 50% of the maximal effect.
• The concentration that occupies 50% of receptors in a binding assay.
• The dose that causes 50% receptor internalization.

Correct Answer: The dose that produces 50% of the maximal effect.

Q18. How is the therapeutic index (TI) calculated?

• TI = ED50 / TD50.
• TI = TD50 / ED50.
• TI = Kd / Bmax.
• TI = intrinsic efficacy × potency.

Correct Answer: TI = TD50 / ED50.

Q19. A Schild plot with a slope close to 1 typically indicates which type of antagonism?

• Noncompetitive antagonism.
• Allosteric modulation.
• Competitive reversible antagonism.
• Irreversible agonism.

Correct Answer: Competitive reversible antagonism.

Q20. The inhibition constant Ki obtained from a radioligand displacement assay represents:

• The maximal number of binding sites.
• The concentration of inhibitor producing 50% of the maximal response.
• The binding affinity of the inhibitor for the receptor.
• The intrinsic efficacy of the inhibitor.

Correct Answer: The binding affinity of the inhibitor for the receptor.

Q21. Activation of G protein‑coupled receptors (GPCRs) commonly leads to:

• Direct DNA replication.
• Synthesis of membrane lipids only.
• Generation of second messengers such as cAMP, IP3 and DAG.
• Immediate receptor degradation without signaling.

Correct Answer: Generation of second messengers such as cAMP, IP3 and DAG.

Q22. Receptor tyrosine kinases (RTKs) are typically activated by which mechanism?

• Ligand‑induced dimerization followed by autophosphorylation.
• Direct G protein exchange.
• Binding of small anions to the orthosteric site.
• Ubiquitin‑mediated nuclear import.

Correct Answer: Ligand‑induced dimerization followed by autophosphorylation.

Q23. A positive allosteric modulator (PAM) generally does what?

• Directly activates the receptor to its full maximal response without agonist.
• Enhances the efficacy or potency of an orthosteric agonist while binding at a different site.
• Irreversibly blocks the orthosteric binding site.
• Causes complete receptor internalization and loss of function.

Correct Answer: Enhances the efficacy or potency of an orthosteric agonist while binding at a different site.

Q24. What does Emax represent in a dose‑response study?

• The dose required to reach 50% receptor occupancy.
• The maximal achievable effect of a drug in that system.
• The equilibrium dissociation constant of an antagonist.
• The baseline activity of receptors without ligand.

Correct Answer: The maximal achievable effect of a drug in that system.

Q25. Which statement is true about surmountable antagonism?

• It cannot be overcome by increasing agonist concentration.
• It is typically seen with irreversible antagonists.
• It can be overcome by increasing agonist concentration, characteristic of competitive antagonists.
• It always reduces the Emax of the agonist.

Correct Answer: It can be overcome by increasing agonist concentration, characteristic of competitive antagonists.

Q26. Non‑surmountable antagonism implies:

• The antagonism can be reversed by adding more agonist.
• The antagonism reduces the maximal response even with high agonist concentrations.
• The antagonist increases agonist potency without affecting Emax.
• The antagonist functions as a positive allosteric modulator.

Correct Answer: The antagonism reduces the maximal response even with high agonist concentrations.

Q27. How does an inverse agonist differ from a neutral antagonist?

• Inverse agonists produce the same effect as full agonists.
• Inverse agonists reduce constitutive receptor activity, whereas neutral antagonists block agonist binding without altering basal activity.
• Neutral antagonists decrease basal activity, inverse agonists do not bind receptors.
• There is no pharmacological difference between them.

Correct Answer: Inverse agonists reduce constitutive receptor activity, whereas neutral antagonists block agonist binding without altering basal activity.

Q28. Which finding suggests the presence of spare receptors in a tissue?

• A Kd value much lower than EC50.
• EC50 is less than Kd, indicating a lower concentration is needed for half‑maximal effect than for half receptor occupancy.
• A maximal response cannot be achieved even at very high agonist concentrations.
• Linear correlation between Bmax and EC50.

Correct Answer: EC50 is less than Kd, indicating a lower concentration is needed for half‑maximal effect than for half receptor occupancy.

Q29. In the presence of a full agonist, a partial agonist will often act as:

• A full agonist producing increased maximal effect.
• An inverse agonist reducing basal activity only.
• An antagonist that reduces the response by competing for receptors.
• A neutral ligand with no effect on response.

Correct Answer: An antagonist that reduces the response by competing for receptors.

Q30. Which statement about Kd and affinity is correct?

• A higher Kd indicates greater affinity of ligand for receptor.
• Kd is unrelated to binding affinity and measures efficacy.
• A lower Kd indicates a higher affinity of the ligand for the receptor.
• Kd equals the maximal response divided by potency.

Correct Answer: A lower Kd indicates a higher affinity of the ligand for the receptor.

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com