Classification and structure of receptor families MCQs With Answer

Introduction: This quiz set on the classification and structure of receptor families is tailored for M.Pharm students to reinforce core concepts in cellular and molecular pharmacology. Through focused multiple-choice questions, you will review structural motifs, transmembrane organization, domain architecture, dimerization patterns, and principal signaling mechanisms across major receptor families (GPCRs, ionotropic receptors, nuclear receptors, receptor tyrosine kinases, cytokine receptors, guanylyl cyclases, integrins, and innate immune receptors). Questions emphasize molecular details such as zinc-finger domains, SH2/SH3 interactions, G-protein coupling specificity, and ligand-binding domain location—areas frequently tested in advanced pharmacology courses and useful for drug-target analysis.

Q1. Which primary structural criterion is commonly used to classify membrane receptor families?

• Number of transmembrane helices
• Molecular weight of the receptor protein
• Rate of ligand dissociation
• Cellular sublocalization only

Correct Answer: Number of transmembrane helices

Q2. Which structural feature defines the G protein–coupled receptor (GPCR) superfamily?

• Single transmembrane helix and large cytosolic kinase domain
• Seven transmembrane alpha-helices with extracellular N-terminus and intracellular C-terminus
• Tetrameric ion channel with pore-forming beta-sheets
• Intracellular ligand-binding zinc-finger motif

Correct Answer: Seven transmembrane alpha-helices with extracellular N-terminus and intracellular C-terminus

Q3. Which of the following receptors is an ionotropic (ligand-gated ion channel) receptor?

• Nicotinic acetylcholine receptor (nAChR)
• Beta-2 adrenergic receptor
• Insulin receptor
• Glucocorticoid receptor

Correct Answer: Nicotinic acetylcholine receptor (nAChR)

Q4. What is the characteristic DNA-binding structural motif of classical nuclear steroid hormone receptors?

• Leucine zipper motif
• PDZ domain
• Zinc-finger motif (C4-type)
• Pleckstrin homology (PH) domain

Correct Answer: Zinc-finger motif (C4-type)

Q5. Activation of most receptor tyrosine kinases (RTKs) involves which immediate mechanistic step?

• GDP to GTP exchange on small G-proteins
• Ligand-induced dimerization followed by trans-autophosphorylation of tyrosine residues
• Direct binding to intracellular DNA response elements
• Cleavage of an intracellular transcription factor domain

Correct Answer: Ligand-induced dimerization followed by trans-autophosphorylation of tyrosine residues

Q6. Which statement best describes the classical cytokine receptor (type I/II) signaling mechanism?

• They possess intrinsic tyrosine kinase domains and phosphorylate STATs directly
• They are GPCRs that activate adenylyl cyclase
• They lack intrinsic kinase activity and signal by associating with Janus kinases (JAKs) to activate STAT transcription factors
• They function as ion channels increasing intracellular Ca2+

Correct Answer: They lack intrinsic kinase activity and signal by associating with Janus kinases (JAKs) to activate STAT transcription factors

Q7. Which receptor is a membrane-associated guanylyl cyclase that produces cGMP upon ligand binding?

• Atrial natriuretic peptide (ANP) receptor (GC-A)
• Nitric oxide–activated soluble guanylyl cyclase
• Beta adrenergic receptor
• NMDA receptor

Correct Answer: Atrial natriuretic peptide (ANP) receptor (GC-A)

Q8. Which endocytic pathway is most commonly involved in ligand-induced internalization and down-regulation of many cell-surface receptors?

• Clathrin-mediated endocytosis
• Autophagy-mediated sequestration
• Proteasome-mediated internalization
• Passive diffusion across the membrane

Correct Answer: Clathrin-mediated endocytosis

Q9. Integrin receptors are structurally characterized by which arrangement?

• Single polypeptide with seven transmembrane domains
• Heterodimeric assembly of non-covalently associated alpha and beta subunits
• Homodimeric nuclear receptor with zinc-finger DNA binding
• Ion channel tetramer with each subunit composed of beta-sheets

Correct Answer: Heterodimeric assembly of non-covalently associated alpha and beta subunits

Q10. In classical nuclear receptors, where is the primary ligand-binding domain (LBD) located relative to the DNA-binding domain (DBD)?

• N-terminal to the DBD
• C-terminal to the DBD
• Within the transmembrane region
• There is no discrete LBD in nuclear receptors

Correct Answer: C-terminal to the DBD

Q11. Activation of adenylyl cyclase by a receptor through Gs protein results in which immediate change?

• Decrease in intracellular cAMP concentration
• Increase in intracellular cAMP concentration
• Direct phosphorylation of tyrosine residues on the receptor
• Opening of a ligand-gated chloride channel

Correct Answer: Increase in intracellular cAMP concentration

Q12. Which unique biophysical property distinguishes the NMDA subtype of ionotropic glutamate receptors?

• Voltage-dependent Mg2+ block and high Ca2+ permeability
• Exclusive permeability to chloride ions
• Constitutive activity in absence of ligand
• Direct G-protein coupling without second messengers

Correct Answer: Voltage-dependent Mg2+ block and high Ca2+ permeability

Q13. Which modular protein interaction domain specifically recognizes phosphotyrosine-containing motifs on activated receptors?

• SH2 (Src homology 2) domain
• PH (pleckstrin homology) domain
• C2 domain
• EF-hand calcium-binding motif

Correct Answer: SH2 (Src homology 2) domain

Q14. Which receptor family uses intrinsic serine/threonine kinase activity to phosphorylate downstream SMAD proteins?

• TGF-β receptor family (type I/II serine/threonine kinases)
• GPCR family
• Ionotropic glutamate receptors
• Receptor tyrosine phosphatases

Correct Answer: TGF-β receptor family (type I/II serine/threonine kinases)

Q15. What molecular events are central to homologous desensitization of GPCRs after prolonged agonist exposure?

• Proteolytic cleavage of the receptor extracellular domain by metalloproteases
• Phosphorylation by G protein–coupled receptor kinases (GRKs) followed by arrestin binding
• Immediate internalization via ubiquitin-independent lysosomal targeting
• Conversion of GPCR into a nuclear transcription factor

Correct Answer: Phosphorylation by G protein–coupled receptor kinases (GRKs) followed by arrestin binding

Q16. What defines an ‘orphan receptor’ in receptor pharmacology?

• A receptor expressed only during embryogenesis
• A receptor whose endogenous ligand is unknown or has not been identified
• A receptor that signals constitutively without ligand
• A receptor localized only to mitochondria

Correct Answer: A receptor whose endogenous ligand is unknown or has not been identified

Q17. Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns using which extracellular structural motif?

• Leucine-rich repeat (LRR) domains
• Zinc-finger DNA-binding domains
• Seven transmembrane helices
• PDZ interaction motifs

Correct Answer: Leucine-rich repeat (LRR) domains

Q18. What is the typical subunit stoichiometry of the neuronal nicotinic acetylcholine receptor?

• Trimeric assembly of three identical subunits
• Pentameric assembly of five subunits
• Dimeric alpha-beta heterodimer
• Monomeric single-chain pore-forming protein

Correct Answer: Pentameric assembly of five subunits

Q19. Many nuclear receptors (e.g., thyroid hormone receptor) commonly form which type of dimer for high-affinity DNA binding?

• Obligate heterodimer with retinoid X receptor (RXR)
• Heterotrimer with GPCR and RTK
• Membrane-anchored homodimer via transmembrane helices
• Non-specific aggregation without defined dimer interface

Correct Answer: Obligate heterodimer with retinoid X receptor (RXR)

Q20. Which structural organization best describes a typical receptor tyrosine kinase (RTK)?

• Extracellular ligand-binding domain, single transmembrane helix, intracellular tyrosine kinase domain
• Seven transmembrane helices with intracellular G-protein coupling
• Pore-forming beta-barrel spanning the membrane multiple times
• Primarily nuclear localization with zinc-finger DNA-binding domain

Correct Answer: Extracellular ligand-binding domain, single transmembrane helix, intracellular tyrosine kinase domain

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