Receptors for cell signals MCQs With Answer

Receptors for cell signals are central to pharmacology, mediating how drugs and endogenous ligands control cellular responses. This topic covers receptor families such as G-protein coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), ion channel receptors, and intracellular/nuclear receptors, plus concepts like ligand binding, second messengers (cAMP, IP3/DAG, Ca2+), signal transduction, desensitization, internalization, and receptor kinetics (KD, EC50). Understanding agonists, antagonists, partial agonists, inverse agonists, allosteric modulators, and biased signaling is essential for rational drug design and therapeutic targeting. Keywords: GPCR, RTK, ion channel, nuclear receptor, second messenger, signal amplification, pharmacology. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which receptor family primarily signals through heterotrimeric G-proteins to modulate intracellular second messengers?

• Receptor tyrosine kinases
• G-protein coupled receptors
• Ligand-gated ion channels
• Nuclear steroid receptors

Correct Answer: G-protein coupled receptors

Q2. Which second messenger is directly produced by adenylyl cyclase activation?

• Diacylglycerol (DAG)
• Inositol trisphosphate (IP3)
• cAMP
• cGMP

Correct Answer: cAMP

Q3. Receptor tyrosine kinases (RTKs) activate downstream signalling primarily by which immediate molecular event?

• Ligand-gated ion flux
• GTP hydrolysis
• Autophosphorylation on tyrosine residues
• Direct DNA binding

Correct Answer: Autophosphorylation on tyrosine residues

Q4. Which receptor type typically acts as a transcription factor after ligand binding and nuclear translocation?

• GPCRs
• RTKs
• Ligand-gated ion channels
• Nuclear steroid receptors

Correct Answer: Nuclear steroid receptors

Q5. What is the pharmacological definition of a partial agonist?

• A ligand that blocks receptor binding without intrinsic activity
• A ligand that produces a maximal response greater than full agonist
• A ligand that produces lower maximal efficacy than a full agonist
• A ligand that only binds allosteric sites

Correct Answer: A ligand that produces lower maximal efficacy than a full agonist

Q6. Which mechanism describes decreased receptor responsiveness following prolonged exposure to an agonist?

• Upregulation
• Desensitization
• Sensitization
• Allosteric potentiation

Correct Answer: Desensitization

Q7. Arrestins are primarily involved in which receptor-related process for GPCRs?

• Enhancing G-protein activation
• Receptor internalization and signaling bias
• Tyrosine phosphorylation of receptors
• Direct activation of adenylyl cyclase

Correct Answer: Receptor internalization and signaling bias

Q8. The dissociation constant (KD) of a receptor-ligand pair represents:

• The ligand concentration producing half-maximal effect
• The ligand concentration at which half the receptors are occupied
• The maximal response achievable by a ligand
• The rate of receptor internalization

Correct Answer: The ligand concentration at which half the receptors are occupied

Q9. Which secondary messenger results from phospholipase C (PLC) activity?

• cAMP only
• IP3 and DAG
• cGMP and nitric oxide
• ATP

Correct Answer: IP3 and DAG

Q10. Noncompetitive antagonists most commonly reduce agonist response by:

• Competing for the same orthosteric binding site
• Irreversibly or allosterically inhibiting receptor function
• Increasing receptor expression
• Enhancing agonist affinity

Correct Answer: Irreversibly or allosterically inhibiting receptor function

Q11. Which term describes receptors present in excess such that maximal response occurs without full occupancy?

• Allosteric receptors
• Spare receptors
• Desensitized receptors
• Orphan receptors

Correct Answer: Spare receptors

Q12. Biased agonism refers to:

• Agonists that only bind one receptor subtype
• Ligands that selectively activate certain downstream pathways over others via the same receptor
• Agonists that cannot be displaced by antagonists
• Ligands that lack intrinsic efficacy

Correct Answer: Ligands that selectively activate certain downstream pathways over others via the same receptor

Q13. An inverse agonist differs from a neutral antagonist by:

• Binding irreversibly
• Reducing constitutive receptor activity below basal levels
• Increasing agonist efficacy
• Acting only at allosteric sites

Correct Answer: Reducing constitutive receptor activity below basal levels

Q14. Which event follows IP3 generation in many signal transduction pathways?

• Activation of guanylyl cyclase
• Release of Ca2+ from endoplasmic reticulum stores
• Direct phosphorylation of transcription factors
• cAMP degradation

Correct Answer: Release of Ca2+ from endoplasmic reticulum stores

Q15. Which receptor class mediates fastest synaptic transmission by permitting ion flow upon ligand binding?

• GPCRs
• Ionotropic (ligand-gated) ion channel receptors
• RTKs
• Nuclear receptors

Correct Answer: Ionotropic (ligand-gated) ion channel receptors

Q16. Which process commonly follows agonist-induced phosphorylation of GPCRs by G protein-coupled receptor kinases (GRKs)?

• Receptor tyrosine phosphorylation
• Ubiquitin-independent degradation
• Arrestin recruitment and internalization
• Direct activation of adenylyl cyclase

Correct Answer: Arrestin recruitment and internalization

Q17. The MAPK/ERK pathway is typically activated downstream of which receptor family?

• Voltage-gated ion channels
• Receptor tyrosine kinases and some GPCRs
• Nuclear receptors only
• Ligand-gated chloride channels

Correct Answer: Receptor tyrosine kinases and some GPCRs

Q18. Allosteric modulators bind to:

• The orthosteric (active) binding site exclusively
• Distinct sites on the receptor to modulate function
• Receptor mRNA to alter translation
• Cell membrane lipids to change fluidity

Correct Answer: Distinct sites on the receptor to modulate function

Q19. JAK-STAT signalling is primarily associated with which receptor type?

• G-protein coupled receptors
• Cytokine receptors lacking intrinsic kinase activity
• Ligand-gated ion channels
• Nuclear hormone receptors

Correct Answer: Cytokine receptors lacking intrinsic kinase activity

Q20. Which parameter best describes drug potency in functional assays?

• KD (dissociation constant)
• EC50 (concentration producing 50% maximal effect)
• Bmax (maximum binding capacity)
• pKb (antagonist equilibrium constant)

Correct Answer: EC50 (concentration producing 50% maximal effect)

Q21. Heterodimerization of receptors can lead to:

• Loss of ligand specificity only
• Novel signalling properties and altered pharmacology
• Immediate receptor degradation only
• Universal receptor insensitivity

Correct Answer: Novel signalling properties and altered pharmacology

Q22. Which type of antagonist increases the apparent KD of an agonist without changing the maximal response (if surmountable)?

• Noncompetitive antagonist
• Allosteric antagonist
• Competitive reversible antagonist
• Irreversible antagonist

Correct Answer: Competitive reversible antagonist

Q23. Which receptor-targeted strategy can provide tissue-selective modulation while sparing global receptor blockade?

• Using high doses of orthosteric antagonists
• Designing subtype-selective orthosteric ligands or allosteric modulators
• Using non-specific enzyme inhibitors
• Blocking receptor gene transcription systemically

Correct Answer: Designing subtype-selective orthosteric ligands or allosteric modulators

Q24. Which phrase best describes receptor upregulation after chronic antagonist treatment?

• Decrease in receptor number
• Increase in receptor number or sensitivity
• Immediate receptor internalization
• Permanent receptor gene mutation

Correct Answer: Increase in receptor number or sensitivity

Q25. Which enzyme degrades cAMP to terminate its signaling?

• Phospholipase C
• Adenylyl cyclase
• Protein kinase A
• Phosphodiesterase

Correct Answer: Phosphodiesterase

Q26. A drug that shifts the agonist dose-response curve to the right without reducing the maximal response is likely a:

• Noncompetitive antagonist
• Competitive antagonist
• Partial agonist
• Inverse agonist

Correct Answer: Competitive antagonist

Q27. Which molecular feature is characteristic of GPCRs?

• Single transmembrane helix
• Seven transmembrane helices
• Intrinsic tyrosine kinase domain
• DNA-binding zinc fingers

Correct Answer: Seven transmembrane helices

Q28. Which downstream effector is directly activated by Gq alpha subunit?

• Adenylyl cyclase
• Phospholipase C-β (PLC-β)
• Guanylyl cyclase
• Tyrosine kinase

Correct Answer: Phospholipase C-β (PLC-β)

Q29. Which assay best measures receptor-ligand binding affinity independent of functional response?

• Functional cAMP accumulation assay
• Radioligand binding assay measuring KD and Bmax
• Calcium imaging only
• Western blot for downstream kinases

Correct Answer: Radioligand binding assay measuring KD and Bmax

Q30. Orphan receptors are defined as:

• Receptors with no known endogenous ligand or function
• Receptors permanently active without ligands
• Receptors exclusively located in mitochondria
• Only bacterial receptors

Correct Answer: Receptors with no known endogenous ligand or function

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