Classification of receptors is a foundational topic in pharmacology for B.Pharm students. Understanding receptor types — including ionotropic (ligand-gated channels), metabotropic G-protein coupled receptors (GPCRs), enzyme-linked receptors (receptor tyrosine kinases), intracellular/nuclear receptors, guanylyl cyclase receptors, and cytokine receptors — clarifies how drugs produce effects via signal transduction. Key concepts covered are ligand specificity, transducer mechanisms, second messengers, receptor affinity and efficacy, desensitization, and receptor regulation. Linking receptor classification to pharmacodynamics and drug design helps predict therapeutic responses and adverse effects, with examples such as adrenergic, cholinergic and steroid receptors. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which class of receptor directly forms an ion-selective pore that opens on ligand binding?
- G-protein coupled receptor
- Receptor tyrosine kinase
- Ligand-gated ion channel
- Nuclear receptor
Correct Answer: Ligand-gated ion channel
Q2. Which receptor family primarily signals through heterotrimeric G proteins and second messengers?
- Ionotropic receptors
- G-protein coupled receptors (GPCRs)
- Receptor tyrosine kinases (RTKs)
- Nuclear steroid receptors
Correct Answer: G-protein coupled receptors (GPCRs)
Q3. Receptor tyrosine kinases (RTKs) typically exert their effect by:
- Opening ion channels directly
- Activating intrinsic kinase activity and phosphorylating tyrosine residues
- Binding DNA as transcription factors without phosphorylation
- Directly generating cyclic GMP
Correct Answer: Activating intrinsic kinase activity and phosphorylating tyrosine residues
Q4. Nuclear receptors usually regulate cellular responses by:
- Altering membrane ion permeability
- Activating G proteins at the cell surface
- Binding ligand, then DNA to modulate gene transcription
- Directly phosphorylating cytosolic enzymes
Correct Answer: Binding ligand, then DNA to modulate gene transcription
Q5. Which receptor type is most associated with rapid synaptic transmission in the CNS?
- Nuclear receptors
- Ligand-gated ion channels
- Receptor tyrosine kinases
- Cytokine receptors
Correct Answer: Ligand-gated ion channels
Q6. The beta-adrenergic receptor is best categorized as which receptor class?
- Ionotropic receptor
- GPCR (metabotropic)
- Receptor tyrosine kinase
- Intracellular nuclear receptor
Correct Answer: GPCR (metabotropic)
Q7. Which receptor mechanism commonly uses cAMP as a second messenger?
- Guanylyl cyclase receptors
- GPCRs coupled to Gs proteins
- Receptor tyrosine kinases activating Ras
- Nuclear receptors binding hormone response elements
Correct Answer: GPCRs coupled to Gs proteins
Q8. Cytokine receptors typically signal via which intracellular cascade?
- cAMP-PKA pathway
- JAK-STAT pathway
- Direct ion flux through pores
- cGMP-dependent protein kinase only
Correct Answer: JAK-STAT pathway
Q9. Which property describes receptor affinity?
- Maximal response produced by a drug
- Concentration of ligand producing half-maximal effect
- Tendency of a receptor to be internalized
- Strength of binding between ligand and receptor
Correct Answer: Strength of binding between ligand and receptor
Q10. A partial agonist is best defined as a ligand that:
- Produces no response and blocks agonists
- Produces a maximal response like a full agonist
- Produces less than maximal response even at full receptor occupancy
- Irreversibly activates receptors
Correct Answer: Produces less than maximal response even at full receptor occupancy
Q11. Spare receptors refer to:
- Receptors that are permanently inactive
- Excess receptors such that maximal response occurs without full occupancy
- Receptors located only in intracellular compartments
- Receptors that bind irreversible antagonists
Correct Answer: Excess receptors such that maximal response occurs without full occupancy
Q12. Desensitization of GPCRs often involves:
- Increased gene transcription by nuclear receptors
- Phosphorylation by GRKs and arrestin binding
- Direct cleavage of receptors by proteases at the synapse
- Conversion to ligand-gated ion channels
Correct Answer: Phosphorylation by GRKs and arrestin binding
Q13. An inverse agonist differs from a neutral antagonist by:
- Binding irreversibly to the receptor
- Reducing constitutive receptor activity below basal levels
- Activating the receptor to produce a response
- Only blocking ligand binding without affecting basal activity
Correct Answer: Reducing constitutive receptor activity below basal levels
Q14. Which receptor class directly synthesizes cGMP when activated?
- Nuclear steroid receptors
- Membrane guanylyl cyclase receptors
- Ligand-gated ion channels
- Receptor tyrosine kinases
Correct Answer: Membrane guanylyl cyclase receptors
Q15. Pattern recognition receptors (PRRs) like Toll-like receptors are primarily important for:
- Synaptic neurotransmission
- Innate immune detection of pathogens
- Steroid hormone-mediated gene regulation
- Regulating ion channel opening in muscle
Correct Answer: Innate immune detection of pathogens
Q16. The dissociation constant (Kd) of a ligand-receptor interaction represents:
- Ligand concentration at which receptor is fully saturated
- Ligand concentration at which half of receptors are occupied
- Maximum possible effect of a drug
- Rate of receptor internalization
Correct Answer: Ligand concentration at which half of receptors are occupied
Q17. Which statement correctly contrasts ionotropic and metabotropic receptors?
- Ionotropic receptors are slower and use second messengers; metabotropic are fast ion channels
- Ionotropic receptors form channels for ions; metabotropic receptors act via G proteins and second messengers
- Both types always act as transcription factors
- Metabotropic receptors are localized only in the nucleus
Correct Answer: Ionotropic receptors form channels for ions; metabotropic receptors act via G proteins and second messengers
Q18. Which receptor subtype primarily mediates smooth muscle contraction via IP3 and DAG production?
- Beta-2 adrenergic receptor
- Alpha-1 adrenergic receptor
- Muscarinic M2 receptor
- Glucocorticoid receptor
Correct Answer: Alpha-1 adrenergic receptor
Q19. Biased agonism refers to:
- An agonist that only binds irreversibly
- A ligand preferentially activating one signaling pathway over another via the same receptor
- A ligand that produces identical responses in all tissues
- Only antagonists that block biased receptors
Correct Answer: A ligand preferentially activating one signaling pathway over another via the same receptor
Q20. Which receptor classification is based on the cellular location of receptors (surface vs intracellular)?
- Classification by ligand potency
- Classification by transducer mechanism
- Classification by localization (membrane vs intracellular)
- Classification by therapeutic index
Correct Answer: Classification by localization (membrane vs intracellular)
Q21. A competitive antagonist typically changes which characteristic of an agonist dose-response curve?
- Decreases maximal response without shifting curve
- Shifts the curve to the right without changing the maximal response
- Increases potency of the agonist
- Converts agonist into inverse agonist
Correct Answer: Shifts the curve to the right without changing the maximal response
Q22. Which receptor family includes insulin receptors?
- GPCR family
- Receptor tyrosine kinase (RTK) family
- Ligand-gated ion channel family
- Nuclear receptor family
Correct Answer: Receptor tyrosine kinase (RTK) family
Q23. Allosteric modulators act at sites:
- Identical to the endogenous ligand binding site only
- Different from the orthosteric site and modify receptor response
- That permanently activate receptors regardless of ligand
- That always cause receptor internalization
Correct Answer: Different from the orthosteric site and modify receptor response
Q24. Which measurement estimates the total number of receptors in a tissue (Bmax) using radioligand binding?
- EC50
- Kd
- Bmax
- Therapeutic index
Correct Answer: Bmax
Q25. Which receptor responds to intracellular steroid hormones like cortisol?
- Nuclear steroid receptors
- Ligand-gated ion channels
- GPCRs coupled to Gi proteins
- Membrane guanylyl cyclase receptors
Correct Answer: Nuclear steroid receptors
Q26. Tachyphylaxis refers to:
- Slow genomic effects of nuclear receptors
- A rapid decrease in response to repeated drug administration
- Enhanced response after continuous exposure
- Only observed with irreversible antagonists
Correct Answer: A rapid decrease in response to repeated drug administration
Q27. Which receptor type commonly dimerizes upon ligand binding to initiate signaling?
- Receptor tyrosine kinases
- Ligand-gated ion channels exclusively
- Nuclear receptors never dimerize
- All GPCRs always dimerize
Correct Answer: Receptor tyrosine kinases
Q28. Which classification criterion groups receptors by the chemical nature of the ligand (e.g., peptide, steroid, amine)?
- Classification by transducer mechanism
- Classification by ligand type
- Classification by anatomical location
- Classification by receptor turnover rate
Correct Answer: Classification by ligand type
Q29. The muscarinic M2 receptor mainly produces cardiac effects by:
- Activating Gs to increase cAMP
- Activating Gi to decrease cAMP and opening K+ channels
- Directly phosphorylating tyrosine residues
- Entering the nucleus to alter gene expression
Correct Answer: Activating Gi to decrease cAMP and opening K+ channels
Q30. Which concept explains why two drugs with similar affinity produce different maximal effects?
- Different intrinsic efficacy (efficacy differences)
- Identical receptor reserve always
- Same potency implies same maximal effect
- Affinity is the sole determinant of maximal effect
Correct Answer: Different intrinsic efficacy (efficacy differences)
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.
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