Structural and functional families of receptors MCQs With Answer

Structural and functional families of receptors MCQs With Answer

This quiz collection is designed for M.Pharm students preparing for Advanced Pharmacology-I. It focuses on the molecular architecture, classification, and signalling mechanisms of major receptor families — including ionotropic receptors, G protein–coupled receptors (GPCRs), receptor tyrosine kinases, cytokine receptors, guanylyl cyclase receptors, and nuclear receptors. Questions probe structural domains, receptor subfamilies, mechanisms of activation and regulation (dimerization, phosphorylation, internalization, biased agonism), and pharmacological implications such as allosteric modulation, receptor reserve, and constitutive activity. The set helps students consolidate conceptual understanding and apply molecular insights to drug action and therapeutic targeting.

Q1. Which structural feature most characterizes class A (rhodopsin-like) G protein–coupled receptors?

• Long extracellular N-terminal domain with ligand-binding LRR repeats
• Seven transmembrane alpha-helices with conserved DRY motif at the cytoplasmic end of TM3
• Single transmembrane helix with intrinsic tyrosine kinase activity
• Intracellular zinc-finger DNA-binding domain

Correct Answer: Seven transmembrane alpha-helices with conserved DRY motif at the cytoplasmic end of TM3

Q2. Which receptor family signals primarily via direct phosphorylation of receptor tyrosine residues and recruitment of SH2-domain adapter proteins?

• Ligand-gated ion channels
• Receptor tyrosine kinases (RTKs)
• Nuclear hormone receptors
• Soluble guanylyl cyclases

Correct Answer: Receptor tyrosine kinases (RTKs)

Q3. Which of the following is a defining functional property of ionotropic (ligand-gated) receptors?

• Activation produces changes in gene transcription via direct DNA binding
• Ligand binding opens an intrinsic ion channel to allow rapid ion flux across the membrane
• Signal transduction exclusively via heterotrimeric G proteins
• Activation causes generation of cyclic GMP through intrinsic cyclase activity

Correct Answer: Ligand binding opens an intrinsic ion channel to allow rapid ion flux across the membrane

Q4. Which receptor is a classic example of a nuclear receptor that acts as a ligand-activated transcription factor?

• Beta-2 adrenergic receptor
• Insulin receptor
• Glucocorticoid receptor
• Nicotinic acetylcholine receptor

Correct Answer: Glucocorticoid receptor

Q5. Soluble guanylyl cyclase (sGC) is activated by which gaseous signalling molecule to increase intracellular cGMP?

• Nitric oxide (NO)
• Carbon dioxide (CO2)
• Oxygen (O2)
• Hydrogen sulfide (H2S)

Correct Answer: Nitric oxide (NO)

Q6. Which mechanism best describes “biased agonism” at GPCRs?

• A ligand that irreversibly blocks the orthosteric site
• A ligand preferentially stabilizes receptor conformations that activate one signalling pathway over another (e.g., G protein vs β-arrestin)
• Complete desensitization caused by prolonged agonist stimulation
• Ligand-induced receptor dimerization required for activation

Correct Answer: A ligand preferentially stabilizes receptor conformations that activate one signalling pathway over another (e.g., G protein vs β-arrestin)

Q7. Which family uses JAK–STAT signalling as a principal downstream pathway?

• Cytokine receptors lacking intrinsic kinase domains
• Ligand-gated chloride channels
• Class C GPCRs such as metabotropic glutamate receptors
• Nuclear receptors like PPARs

Correct Answer: Cytokine receptors lacking intrinsic kinase domains

Q8. Receptor tyrosine kinases often require which event for activation after ligand binding?

• Proteolytic cleavage of the intracellular domain
• Dimerization and trans-autophosphorylation of intracellular kinase domains
• Binding of heterotrimeric G proteins to the C-terminus
• Nuclear translocation as a monomer

Correct Answer: Dimerization and trans-autophosphorylation of intracellular kinase domains

Q9. Which receptor family is characterized by large extracellular ligand-binding Venus flytrap domains and modulatory C-terminal domains, and includes metabotropic glutamate receptors?

• Class A GPCRs
• Class B GPCRs
• Class C GPCRs
• Nuclear hormone receptors

Correct Answer: Class C GPCRs

Q10. Which structural element is typical of ionotropic glutamate receptors (e.g., AMPA, NMDA) but not of GPCRs?

• Seven transmembrane helices
• Ligand-binding domain formed by dimerization of extracellular S1/S2 segments and a transmembrane ion pore formed by multiple subunits
• Intrinsic tyrosine kinase activity in the intracellular tail
• DNA-binding zinc-finger domain

Correct Answer: Ligand-binding domain formed by dimerization of extracellular S1/S2 segments and a transmembrane ion pore formed by multiple subunits

Q11. Constitutive activity of a receptor refers to which phenomenon?

• Receptor is permanently internalized and inactive
• Agonist binding is required for any signalling output
• Receptor exhibits baseline signalling activity in the absence of ligand
• Only inverse agonists can bind

Correct Answer: Receptor exhibits baseline signalling activity in the absence of ligand

Q12. Which receptor type is the primary pharmacological target for benzodiazepines?

• NMDA receptor (ionotropic glutamate)
• GABA-A receptor (ligand-gated chloride channel)
• Beta-adrenergic receptor (GPCR)
• Estrogen receptor (nuclear receptor)

Correct Answer: GABA-A receptor (ligand-gated chloride channel)

Q13. Receptor internalization following agonist stimulation often involves recruitment of which protein that promotes clathrin-mediated endocytosis and can mediate signalling independently?

• Guanine nucleotide exchange factor (GEF)
• β-arrestin
• SH2-domain protein Grb2
• Heat shock protein 90 (Hsp90)

Correct Answer: β-arrestin

Q14. Which receptor type directly generates an intracellular second messenger (cAMP) via activation of intrinsic cyclase activity?

• GPCR coupled to Gs that stimulates membrane adenylate cyclase
• Particulate guanylyl cyclase receptor that produces cGMP
• RTK that phosphorylates tyrosines to generate cAMP
• Cytokine receptor that uses JAK to produce cAMP

Correct Answer: GPCR coupled to Gs that stimulates membrane adenylate cyclase

Q15. Allosteric modulators of receptors typically bind to which site relative to the orthosteric ligand-binding site?

• To the same orthosteric site exclusively, displacing endogenous ligand
• To a distinct topographically separate site that modifies receptor response to the orthosteric ligand
• To intracellular DNA response elements
• To transmembrane beta-sheet regions found only in nuclear receptors

Correct Answer: To a distinct topographically separate site that modifies receptor response to the orthosteric ligand

Q16. Which nuclear receptor heterodimer partner is commonly required for many steroid and thyroid hormone receptors to bind DNA and regulate transcription?

• β-arrestin
• Retinoid X receptor (RXR)
• G protein beta-gamma subunit
• Tyrosine kinase Src

Correct Answer: Retinoid X receptor (RXR)

Q17. Receptor reserve (spare receptors) means which of the following?

• A population of receptors that are permanently inactive and unavailable for signalling
• Maximum tissue response can be achieved without occupancy of all available receptors
• Receptors that are only present during development
• Receptors exclusively located in intracellular organelles

Correct Answer: Maximum tissue response can be achieved without occupancy of all available receptors

Q18. Which molecular mechanism commonly underlies tachyphylaxis (rapid desensitization) to agonists acting on GPCRs?

• Upregulation of receptor transcription
• Receptor phosphorylation by GRKs followed by β-arrestin binding and internalization
• Increased affinity of receptor for G protein
• Conversion of receptor from GPCR class C to class A

Correct Answer: Receptor phosphorylation by GRKs followed by β-arrestin binding and internalization

Q19. Which statement best differentiates soluble guanylyl cyclase (sGC) from membrane-bound particulate guanylyl cyclase receptors?

• sGC is directly activated by peptide hormones while particulate GC is activated by NO
• sGC is a cytosolic heme-containing enzyme activated by NO; particulate GC is a transmembrane receptor activated by natriuretic peptides to produce cGMP
• Both are nuclear receptors that control gene transcription
• Particulate GC generates cAMP whereas sGC generates cGMP

Correct Answer: sGC is a cytosolic heme-containing enzyme activated by NO; particulate GC is a transmembrane receptor activated by natriuretic peptides to produce cGMP

Q20. Which pharmacological strategy can selectively target receptor function without competing at the orthosteric binding site?

• Using a competitive orthosteric antagonist
• Developing an allosteric modulator that changes receptor conformation and efficacy
• Increasing ligand concentration to outcompete antagonist
• Mutating the receptor gene in patients

Correct Answer: Developing an allosteric modulator that changes receptor conformation and efficacy

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