Forms of intracellular signaling – contact-dependent, paracrine, synaptic, endocrine MCQs With Answer

Forms of intracellular signaling – contact-dependent, paracrine, synaptic, endocrine MCQs With Answer

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Understanding forms of intracellular signaling—contact-dependent, paracrine, synaptic, and endocrine—is essential for B. Pharm students. These signaling modes differ by distance, speed, mediators and pharmacological targets: contact-dependent (juxtacrine) uses membrane-bound ligands like Notch; paracrine signaling uses local mediators (histamine, nitric oxide); synaptic signaling uses neurotransmitters for rapid, targeted responses; endocrine signaling uses hormones in blood for long-range effects. Key concepts include receptors, ligands, second messengers (cAMP, IP3, DAG, Ca2+), signal transduction pathways, receptor desensitization and drug modulation. Mastery links physiology to therapeutic targeting and adverse effects. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which form of signaling requires direct cell–cell contact via membrane-bound ligands?

  • Contact-dependent (juxtacrine)
  • Paracrine signaling
  • Synaptic signaling
  • Endocrine signaling

Correct Answer: Contact-dependent (juxtacrine)

Q2. Local signaling that affects nearby cells through secreted mediators is called:

  • Paracrine signaling
  • Endocrine signaling
  • Synaptic signaling
  • Contact-dependent signaling

Correct Answer: Paracrine signaling

Q3. Which signaling mode provides the fastest communication between cells?

  • Synaptic signaling
  • Endocrine signaling
  • Paracrine signaling
  • Contact-dependent signaling

Correct Answer: Synaptic signaling

Q4. Signals that travel long distances via the bloodstream are classified as:

  • Endocrine signaling
  • Paracrine signaling
  • Contact-dependent signaling
  • Synaptic signaling

Correct Answer: Endocrine signaling

Q5. Which of the following is a classic paracrine mediator involved in vasodilation?

  • Nitric oxide
  • Insulin
  • Acetylcholine
  • Thyroxine

Correct Answer: Nitric oxide

Q6. Notch–Delta signaling between adjacent cells is an example of:

  • Contact-dependent (juxtacrine) signaling
  • Endocrine signaling
  • Paracrine signaling
  • Synaptic signaling

Correct Answer: Contact-dependent (juxtacrine) signaling

Q7. Which molecule is commonly released into the synaptic cleft as a neurotransmitter?

  • Acetylcholine
  • Insulin
  • Thyroxine
  • Nitric oxide

Correct Answer: Acetylcholine

Q8. Activation of Gs-coupled GPCRs primarily increases which second messenger?

  • cAMP
  • IP3
  • DAG
  • Ca2+

Correct Answer: cAMP

Q9. Ligand binding to many receptor tyrosine kinases commonly initiates which intracellular cascade?

  • MAP kinase (ERK) cascade
  • cAMP pathway
  • NO–cGMP pathway
  • Ligand-gated ion channel opening

Correct Answer: MAP kinase (ERK) cascade

Q10. Which hormone circulates largely bound to carrier proteins, prolonging its half-life?

  • Thyroxine (T4)
  • Acetylcholine
  • Histamine
  • Nitric oxide

Correct Answer: Thyroxine (T4)

Q11. A common paracrine mediator released during allergic reactions is:

  • Histamine
  • Insulin
  • Thyroxine
  • Acetylcholine

Correct Answer: Histamine

Q12. Which signaling type provides the highest spatial specificity to a single target cell?

  • Synaptic signaling
  • Endocrine signaling
  • Paracrine signaling
  • Contact-dependent signaling

Correct Answer: Synaptic signaling

Q13. Compared to paracrine signals, endocrine signals are typically:

  • Long-range and long-lasting effects
  • Rapid and very short-lived
  • Restricted to membrane-bound ligands
  • Always mediated by gases

Correct Answer: Long-range and long-lasting effects

Q14. G-protein coupled receptors belong to which structural class?

  • Seven-transmembrane (GPCR) receptors
  • Receptor tyrosine kinases
  • Ligand-gated ion channels
  • Nuclear receptors

Correct Answer: Seven-transmembrane (GPCR) receptors

Q15. Nitric oxide exerts many effects by:

  • Activating guanylyl cyclase and increasing cGMP
  • Inhibiting adenylate cyclase and lowering cAMP
  • Directly opening sodium channels
  • Binding to nuclear steroid receptors

Correct Answer: Activating guanylyl cyclase and increasing cGMP

Q16. Receptor desensitization often involves which cellular process?

  • Phosphorylation followed by receptor internalization
  • Immediate transcription of new receptors
  • Permanent ligand binding without removal
  • Secretion of ligand-degrading enzymes into blood

Correct Answer: Phosphorylation followed by receptor internalization

Q17. When a cell secretes a factor that acts back on the same cell, this is called:

  • Autocrine signaling
  • Paracrine signaling
  • Endocrine signaling
  • Synaptic signaling

Correct Answer: Autocrine signaling

Q18. Activation of phospholipase C produces which pair of second messengers?

  • IP3 and DAG
  • cAMP and cGMP
  • Ca2+ and cAMP
  • NO and cGMP

Correct Answer: IP3 and DAG

Q19. Juxtacrine signaling is typically mediated by:

  • Membrane-bound ligands such as Notch/Delta and ephrins
  • Circulating peptide hormones
  • Volatile gases only
  • Diffusible blood-borne carriers

Correct Answer: Membrane-bound ligands such as Notch/Delta and ephrins

Q20. Which hormone acts via intracellular nuclear receptors to modulate gene transcription?

  • Cortisol
  • Acetylcholine
  • Histamine
  • Insulin

Correct Answer: Cortisol

Q21. The typical width of a chemical synaptic cleft is approximately:

  • 20 nanometers
  • 1 micrometer
  • 1 millimeter
  • 1 nanometer

Correct Answer: 20 nanometers

Q22. Which statement best contrasts paracrine and endocrine signaling?

  • Paracrine acts locally and is rapidly degraded; endocrine travels in blood to distant targets
  • Paracrine travels in blood; endocrine acts only on neighboring cells
  • Both always require membrane-bound ligands
  • Endocrine signaling never uses carrier proteins

Correct Answer: Paracrine acts locally and is rapidly degraded; endocrine travels in blood to distant targets

Q23. Beta-adrenergic blockers primarily antagonize which receptor class?

  • Beta-adrenergic receptor (GPCR)
  • Insulin receptor (RTK)
  • Nicotinic acetylcholine receptor (ion channel)
  • Thyroid hormone receptor (nuclear)

Correct Answer: Beta-adrenergic receptor (GPCR)

Q24. Homeostatic regulation of many endocrine axes is achieved mainly by:

  • Negative feedback loops
  • Positive feedback loops only
  • Autocrine amplification exclusively
  • Destruction of receptors

Correct Answer: Negative feedback loops

Q25. A principal role of intracellular second messengers is to:

  • Amplify and distribute the signal within the cell
  • Serve as long-range blood carriers
  • Function only as extracellular matrix components
  • Trigger immediate cell lysis

Correct Answer: Amplify and distribute the signal within the cell

Q26. Which enzyme synthesizes cAMP from ATP?

  • Adenylate cyclase
  • Phospholipase C
  • Guanylyl cyclase
  • Protein kinase A

Correct Answer: Adenylate cyclase

Q27. Activation of many receptor tyrosine kinases requires which immediate event?

  • Ligand-induced dimerization and autophosphorylation
  • G-protein activation without phosphorylation
  • Direct DNA binding by the receptor
  • Formation of gap junctions

Correct Answer: Ligand-induced dimerization and autophosphorylation

Q28. Endocrine glands secrete hormones directly into the:

  • Bloodstream
  • Synaptic cleft
  • Extracellular matrix only
  • Cell membrane bilayer

Correct Answer: Bloodstream

Q29. Which molecule can act both as a neurotransmitter and as a hormone when released into blood?

  • Norepinephrine
  • Insulin
  • Histamine
  • Erythropoietin

Correct Answer: Norepinephrine

Q30. A common downstream consequence of activating many signaling pathways is:

  • Changes in gene transcription and protein expression
  • Immediate membrane rupture in all cases
  • Permanent loss of all receptors
  • No change in cellular behavior

Correct Answer: Changes in gene transcription and protein expression

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