Biological significance of cyclic AMP MCQs With Answer

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Introduction: The biological significance of cyclic AMP MCQs with answer offers B. Pharm students a focused, exam-oriented review of cAMP signaling, regulation, and pharmacological relevance. This concise guide covers cAMP synthesis by adenylate cyclase, degradation by phosphodiesterases, key effectors like PKA and EPAC, physiological roles in heart, smooth muscle, metabolism, immune responses, and clinical drug targets (forskolin, PDE inhibitors, β-agonists/antagonists). Ideal for improving conceptual clarity and retention, these MCQs emphasize mechanisms, assays, and therapeutic implications relevant to pharmacology and drug development. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which enzyme catalyzes the conversion of ATP to cyclic AMP (cAMP)?

  • Adenylate cyclase
  • Guanylate cyclase
  • Phosphodiesterase
  • Protein kinase A

Correct Answer: Adenylate cyclase

Q2. Which G protein alpha subunit stimulates adenylate cyclase activity?

  • Gi alpha
  • Gq alpha
  • Gs alpha
  • G12/13 alpha

Correct Answer: Gs alpha

Q3. cAMP primarily exerts its intracellular effects by activating which protein?

  • Protein kinase C (PKC)
  • Protein kinase A (PKA)
  • MAP kinase
  • Tyrosine kinase

Correct Answer: Protein kinase A (PKA)

Q4. Which drug directly activates adenylate cyclase and increases intracellular cAMP?

  • Forskolin
  • Propranolol
  • Sildenafil
  • Nifedipine

Correct Answer: Forskolin

Q5. Which family of enzymes degrades cAMP to 5′-AMP?

  • Adenylyl cyclases
  • Phosphodiesterases (PDEs)
  • Kinases
  • Phosphatases

Correct Answer: Phosphodiesterases (PDEs)

Q6. Which PDE inhibitor is commonly used as a bronchodilator in COPD due to PDE4 inhibition?

  • Milrinone
  • Roflumilast
  • Sildenafil
  • Theophylline

Correct Answer: Roflumilast

Q7. Binding of cAMP to the regulatory subunit of PKA causes what immediate event?

  • Degradation of catalytic subunits
  • Autophosphorylation of regulatory subunit
  • Release of active catalytic subunits
  • Translocation of PKA to lysosomes

Correct Answer: Release of active catalytic subunits

Q8. Which transcription factor is phosphorylated by PKA to regulate gene expression?

  • NF-κB
  • CREB (cAMP response element-binding protein)
  • STAT3
  • HIF-1α

Correct Answer: CREB (cAMP response element-binding protein)

Q9. Which effector is an alternative direct target of cAMP besides PKA?

  • PKC
  • EPAC (Exchange Protein directly Activated by cAMP)
  • PI3K
  • Ras

Correct Answer: EPAC (Exchange Protein directly Activated by cAMP)

Q10. Cholera toxin causes secretory diarrhea by modifying which component to increase cAMP?

  • Gi alpha, inhibiting adenylate cyclase
  • Gs alpha, constitutively activating adenylate cyclase
  • Gq alpha, activating PLC
  • Regulatory subunit of PKA

Correct Answer: Gs alpha, constitutively activating adenylate cyclase

Q11. Pertussis toxin increases intracellular cAMP by ADP-ribosylating which protein?

  • Gs alpha, enhancing inhibition
  • Gi alpha, preventing inhibition of adenylate cyclase
  • Gq alpha, activating PLC
  • Ras, blocking GTP hydrolysis

Correct Answer: Gi alpha, preventing inhibition of adenylate cyclase

Q12. Which physiological hormone increases cAMP in hepatocytes to promote gluconeogenesis?

  • Insulin
  • Glucagon
  • Somatostatin
  • Leptin

Correct Answer: Glucagon

Q13. In adipocytes, increased cAMP activates HSL (hormone-sensitive lipase) via PKA resulting in:

  • Increased lipogenesis
  • Decreased fatty acid release
  • Increased lipolysis and free fatty acid release
  • Decreased glycerol release

Correct Answer: Increased lipolysis and free fatty acid release

Q14. Which cardiac effect is mediated by β1-adrenergic receptor activation and increased cAMP?

  • Negative inotropy
  • Decreased heart rate
  • Positive inotropy and chronotropy
  • Coronary vasoconstriction only

Correct Answer: Positive inotropy and chronotropy

Q15. Which of these drugs is a selective PDE3 inhibitor used in heart failure to increase cAMP?

  • Milrinone
  • Sildenafil
  • Roflumilast
  • Rolipram

Correct Answer: Milrinone

Q16. How does increased intracellular cAMP generally affect platelet aggregation?

  • Enhances aggregation
  • Has no effect
  • Inhibits aggregation
  • Causes platelet lysis

Correct Answer: Inhibits aggregation

Q17. Which experimental assay is commonly used in the lab to quantify cAMP levels?

  • Western blot for cAMP
  • cAMP ELISA or immunoassay
  • Mass spectrometry only
  • Glucose oxidase assay

Correct Answer: cAMP ELISA or immunoassay

Q18. Which statement about spatial regulation of cAMP is true?

  • cAMP diffuses freely and uniformly throughout the cell
  • AKAPs (A-kinase anchoring proteins) localize PKA and create microdomains of cAMP signaling
  • Phosphodiesterases have no role in compartmentalization
  • Only the nucleus experiences cAMP signaling

Correct Answer: AKAPs (A-kinase anchoring proteins) localize PKA and create microdomains of cAMP signaling

Q19. Which molecule terminates the action of cAMP by hydrolyzing it to 5′-AMP?

  • Adenylate cyclase
  • Phosphodiesterase
  • Protein phosphatase
  • cAMP synthase

Correct Answer: Phosphodiesterase

Q20. Which drug is a nonselective PDE inhibitor and also an adenosine receptor antagonist used as a bronchodilator?

  • Theophylline
  • Sildenafil
  • Milrinone
  • Atropine

Correct Answer: Theophylline

Q21. Which PDE isoform is most closely associated with immune cell regulation and is a target in COPD therapy?

  • PDE1
  • PDE3
  • PDE4
  • PDE5

Correct Answer: PDE4

Q22. Which of the following best describes EPAC function in cAMP signaling?

  • EPAC degrades cAMP
  • EPAC is a guanine nucleotide exchange factor activated by cAMP that modulates Rap GTPases
  • EPAC is a phosphatase inhibited by cAMP
  • EPAC phosphorylates CREB directly

Correct Answer: EPAC is a guanine nucleotide exchange factor activated by cAMP that modulates Rap GTPases

Q23. Which ion channel activity is directly enhanced in cardiac cells by PKA phosphorylation downstream of cAMP?

  • Voltage-gated potassium channels only
  • L-type calcium channels
  • Chloride channels exclusively
  • Gap junction hemichannels

Correct Answer: L-type calcium channels

Q24. Which receptor type typically couples to Gi to reduce cAMP formation?

  • β1-adrenergic receptor
  • Muscarinic M2 receptor
  • β2-adrenergic receptor
  • Histamine H1 receptor

Correct Answer: Muscarinic M2 receptor

Q25. What is the immediate intracellular product when cAMP is hydrolyzed by PDE?

  • ATP
  • 5′-AMP
  • GTP
  • cGMP

Correct Answer: 5′-AMP

Q26. Which bacterial regulatory protein uses cAMP as a co-activator for transcription in E. coli?

  • Lac repressor
  • CRP (cAMP receptor protein) / CAP
  • Sigma factor 70
  • Rho factor

Correct Answer: CRP (cAMP receptor protein) / CAP

Q27. Which physiological effect is commonly mediated by cAMP in bronchial smooth muscle?

  • Bronchoconstriction
  • Bronchodilation through PKA-mediated reduction in intracellular Ca2+
  • Production of mucus only
  • Increased smooth muscle proliferation

Correct Answer: Bronchodilation through PKA-mediated reduction in intracellular Ca2+

Q28. Which second messenger system is primarily activated by Gq-coupled receptors (not cAMP-dependent)?

  • cAMP-PKA pathway
  • IP3/DAG pathway via PLC activation
  • cGMP-PKG pathway
  • cAMP-EPAC exclusively

Correct Answer: IP3/DAG pathway via PLC activation

Q29. In endocrine pancreatic β-cells, increased cAMP generally has which effect on insulin secretion?

  • Inhibits insulin release
  • Enhances insulin secretion
  • No effect on insulin release
  • Causes β-cell apoptosis immediately

Correct Answer: Enhances insulin secretion

Q30. Which laboratory biosensor technique can dynamically monitor cAMP changes in living cells?

  • FRET-based cAMP sensors
  • Standard histology staining
  • Colorimetric glucose tests
  • Electron microscopy

Correct Answer: FRET-based cAMP sensors

Q31. Which statement best reflects cAMP’s role in immune cells?

  • cAMP is pro-inflammatory and increases cytokine release
  • Elevated cAMP generally suppresses immune cell activation and inflammatory responses
  • cAMP has no effect on immune signaling
  • cAMP directly lyses pathogens

Correct Answer: Elevated cAMP generally suppresses immune cell activation and inflammatory responses

Q32. Which drug primarily targets PDE5 and affects cGMP rather than cAMP?

  • Sildenafil
  • Milrinone
  • Roflumilast
  • Rolipram

Correct Answer: Sildenafil

Q33. Which cellular process is directly influenced by cAMP-mediated phosphorylation of transcription factors?

  • Immediate ion channel opening only
  • Long-term changes in gene expression
  • Complete degradation of mRNA
  • Permanent DNA mutation

Correct Answer: Long-term changes in gene expression

Q34. Which statement about PKA isoforms is correct?

  • All cells express only one identical PKA form
  • Different tissues express specific PKA regulatory and catalytic isoforms contributing to signaling specificity
  • PKA does not bind cAMP
  • PKA is a membrane-bound receptor

Correct Answer: Different tissues express specific PKA regulatory and catalytic isoforms contributing to signaling specificity

Q35. Which pharmacological class includes drugs that block β-adrenergic receptors and thus reduce cAMP in target cells?

  • β-agonists
  • β-blockers (β-adrenergic antagonists)
  • ACE inhibitors
  • Calcium channel blockers

Correct Answer: β-blockers (β-adrenergic antagonists)

Q36. What effect does activation of Gi-coupled receptors have on cAMP and PKA activity?

  • Increase cAMP and stimulate PKA
  • No change in cAMP
  • Decrease cAMP and reduce PKA activity
  • Convert cAMP to cGMP

Correct Answer: Decrease cAMP and reduce PKA activity

Q37. Which cellular compartment is commonly involved in cAMP-mediated regulation of gene transcription?

  • Lysosome only
  • Nucleus via phosphorylated CREB and coactivators
  • Mitochondrial matrix exclusively
  • Extracellular matrix

Correct Answer: Nucleus via phosphorylated CREB and coactivators

Q38. Which process in skeletal muscle is promoted by β-adrenergic receptor activation and cAMP signaling?

  • Increased glycogen synthesis
  • Glycogenolysis via activation of phosphorylase kinase
  • Immediate protein degradation exclusively
  • Decrease in glucose uptake only

Correct Answer: Glycogenolysis via activation of phosphorylase kinase

Q39. Which pharmacological agent is known to increase cardiac contractility by increasing intracellular cAMP?

  • Propranolol
  • Dobutamine
  • Carvedilol
  • Verapamil

Correct Answer: Dobutamine

Q40. Which molecular mechanism allows rapid termination of PKA signaling after cAMP decreases?

  • PKA catalytic subunits are permanently active once released
  • Rebinding of regulatory subunits to catalytic subunits when cAMP levels fall
  • Immediate proteolytic degradation of regulatory subunits only
  • Translocation of PKA out of the cell

Correct Answer: Rebinding of regulatory subunits to catalytic subunits when cAMP levels fall

Q41. Which type of receptor uses cAMP as a second messenger to mediate hormone action in many tissues?

  • Ionotropic receptors
  • G protein-coupled receptors (GPCRs) coupled to Gs or Gi
  • Nuclear steroid receptors exclusively
  • Toll-like receptors

Correct Answer: G protein-coupled receptors (GPCRs) coupled to Gs or Gi

Q42. Which effect does increased cAMP have on hepatic PKA targets involved in gluconeogenesis?

  • PKA inactivates transcription factors for gluconeogenesis
  • PKA phosphorylates and activates transcription factors (e.g., CREB) that promote gluconeogenic genes
  • PKA immediately degrades gluconeogenic enzymes
  • cAMP reduces glucose production via insulin-like action

Correct Answer: PKA phosphorylates and activates transcription factors (e.g., CREB) that promote gluconeogenic genes

Q43. Which therapeutic approach targets cAMP signaling to reduce inflammation in COPD?

  • β-agonists only
  • PDE4 inhibitors like roflumilast to raise cAMP in inflammatory cells
  • Sildenafil to increase cGMP only
  • ACE inhibitors to lower blood pressure

Correct Answer: PDE4 inhibitors like roflumilast to raise cAMP in inflammatory cells

Q44. Which statement about cAMP and learning/memory is supported by molecular studies?

  • cAMP-PKA-CREB signaling is implicated in synaptic plasticity and long-term memory formation
  • cAMP has no role in neuronal function
  • Increased cAMP always impairs memory
  • cAMP only affects peripheral tissues

Correct Answer: cAMP-PKA-CREB signaling is implicated in synaptic plasticity and long-term memory formation

Q45. Which of the following is a clinical consequence of excessive cAMP in intestinal epithelial cells?

  • Decreased fluid secretion
  • Secretory diarrhea due to increased chloride and fluid secretion
  • Constipation due to slowed transit
  • Increased nutrient absorption only

Correct Answer: Secretory diarrhea due to increased chloride and fluid secretion

Q46. Which molecular technique could be used to assess PKA substrate phosphorylation as a readout of cAMP activity?

  • RT-PCR for cAMP
  • Western blot using phospho-specific antibodies against PKA substrates
  • Flow cytometry for DNA content only
  • Gram staining

Correct Answer: Western blot using phospho-specific antibodies against PKA substrates

Q47. Which regulatory proteins anchor PKA near substrates and contribute to cAMP signaling specificity?

  • A-kinase anchoring proteins (AKAPs)
  • Heat shock proteins only
  • GAPs exclusively
  • Translation initiation factors

Correct Answer: A-kinase anchoring proteins (AKAPs)

Q48. Which physiological response in vascular smooth muscle is generally promoted by elevated cAMP?

  • Vasoconstriction through increased Ca2+
  • Vasodilation via reduced myosin light chain phosphorylation
  • Endothelial cell apoptosis only
  • Increased platelet aggregation in vessels

Correct Answer: Vasodilation via reduced myosin light chain phosphorylation

Q49. Which of these best explains how cAMP influences metabolic enzyme activity acutely?

  • cAMP irreversibly modifies enzymes by acetylation
  • PKA-mediated phosphorylation rapidly alters enzyme activity (activation or inhibition)
  • cAMP directly binds and degrades enzymes
  • cAMP causes enzyme transcription only after days

Correct Answer: PKA-mediated phosphorylation rapidly alters enzyme activity (activation or inhibition)

Q50. Which pharmacological strategy could decrease pathological cAMP elevation caused by cholera toxin?

  • Administration of forskolin to further increase cAMP
  • Use of agents that inhibit adenylate cyclase or enhance PDE activity to lower cAMP
  • Injecting cAMP directly into intestinal lumen
  • Blocking insulin receptors

Correct Answer: Use of agents that inhibit adenylate cyclase or enhance PDE activity to lower cAMP

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