Prostaglandins, Leukotrienes & Thromboxanes: Chemistry and relevance MCQs With Answer

Introduction: This quiz collection on Prostaglandins, Leukotrienes & Thromboxanes: Chemistry and relevance is designed for M.Pharm students studying MPC 103T Advanced Medicinal Chemistry. It emphasizes the chemical structures, biosynthetic pathways, stereochemistry, enzymology, receptor pharmacology and therapeutic relevance of eicosanoids. Questions probe deep concepts such as cyclooxygenase and lipoxygenase mechanisms, key intermediates (PGG2/PGH2/LTA4), transcellular synthesis, instability of TXA2, analytical methods and clinically important modulators (aspirin, prostacyclin analogs, leukotriene modifiers). The set is targeted to strengthen conceptual understanding and application in drug design, pharmacology and formulation contexts relevant to advanced pharmacy practice.

Q1. Which fatty acid is the primary precursor for prostaglandin, leukotriene, and thromboxane biosynthesis?

• Arachidonic acid (20:4, ω-6)
• Linoleic acid (18:2, ω-6)
• Eicosapentaenoic acid (20:5, ω-3)
• Palmitic acid (16:0)

Correct Answer: Arachidonic acid (20:4, ω-6)

Q2. What is the immediate enzymatic product of the cyclooxygenase (COX) activity acting on arachidonic acid?

• PGH2
• LTA4
• Thromboxane A2
• PGG2

Correct Answer: PGG2

Q3. Aspirin irreversibly inhibits which enzyme by acetylation of a serine residue, producing long-lasting antiplatelet effects?

• Cyclooxygenase-1 (COX-1) by acetylation of Ser530
• Cyclooxygenase-2 (COX-2) by phosphorylation
• Thromboxane synthase by competitive inhibition
• 5-Lipoxygenase by iron chelation

Correct Answer: Cyclooxygenase-1 (COX-1) by acetylation of Ser530

Q4. Which enzyme is primarily responsible for generating LTA4 from arachidonic acid in leukotriene biosynthesis?

• 5-Lipoxygenase (5-LOX)
• Cyclooxygenase-1 (COX-1)
• 12-Lipoxygenase (12-LOX)
• Prostaglandin synthase

Correct Answer: 5-Lipoxygenase (5-LOX)

Q5. Which receptor mediates thromboxane A2-induced platelet aggregation and vasoconstriction?

• EP1 receptor
• TP receptor
• BLT1 receptor
• CysLT1 receptor

Correct Answer: TP receptor

Q6. Which prostaglandin is primarily responsible for uterine smooth muscle contraction and is used clinically to induce labor?

• PGE2 (Dinoprostone)
• PGF2α (Dinoprost)
• PGI2 (Prostacyclin)
• TXA2 (Thromboxane A2)

Correct Answer: PGF2α (Dinoprost)

Q7. Which prostanoid is a potent vasodilator and inhibitor of platelet aggregation, synthesized by endothelial cells?

• TXA2 (Thromboxane A2)
• PGI2 (Prostacyclin)
• PGE2 (Prostaglandin E2)
• PGF2α (Prostaglandin F2α)

Correct Answer: PGI2 (Prostacyclin)

Q8. Which of the following drugs is a selective cysteinyl leukotriene receptor (CysLT1) antagonist used in asthma?

• Zileuton
• Montelukast
• Aspirin
• Alprostadil

Correct Answer: Montelukast

Q9. Which intermediate is the immediate precursor for synthesis of the cysteinyl leukotrienes (LTC4, LTD4, LTE4)?

• LTA4
• LTB4
• LTE4
• PGH2

Correct Answer: LTA4

Q10. Which statement best describes thromboxane A2 (TXA2) chemical stability?

• Highly stable with a plasma half-life of several hours and excreted unchanged
• Highly unstable with a half-life of seconds and non-enzymatically hydrolyzes to TXB2
• Stable only at acidic pH and converted to isoprostanes enzymatically
• Exists as a stable glycosylated prodrug until activated by platelets

Correct Answer: Highly unstable with a half-life of seconds and non-enzymatically hydrolyzes to TXB2

Q11. Aspirin-triggered lipoxins are formed because acetylated COX-2 produces which stereospecific intermediate?

• 11R-HETE leading to 11-epi-lipoxin formation
• 15R-HETE leading to 15-epi-lipoxin formation
• 5S-HETE leading to LTB4 formation
• 9R-HETE leading to resolvin formation

Correct Answer: 15R-HETE leading to 15-epi-lipoxin formation

Q12. Which analytical technique provides the highest specificity and sensitivity for quantitative profiling of prostaglandins and leukotrienes in biological samples?

• Enzyme-linked immunosorbent assay (ELISA)
• Radioimmunoassay (RIA)
• LC-MS/MS (liquid chromatography–tandem mass spectrometry)
• Thin-layer chromatography (TLC)

Correct Answer: LC-MS/MS (liquid chromatography–tandem mass spectrometry)

Q13. Which endoperoxide acts as the common substrate for downstream synthases that generate specific prostaglandins and thromboxanes?

• PGG2
• PGH2
• LTA4
• Arachidonic acid

Correct Answer: PGH2

Q14. Which of the following is a clinically used prostacyclin (PGI2) analog for pulmonary arterial hypertension?

• Epoprostenol
• Misoprostol
• Dinoprostone
• Zileuton

Correct Answer: Epoprostenol

Q15. Which leukotriene is a major neutrophil chemoattractant and activator implicated in inflammation?

• LTB4
• LTC4
• LTD4
• LTE4

Correct Answer: LTB4

Q16. Which enzyme converts PGH2 to thromboxane A2 (TXA2) in platelets?

• Thromboxane synthase (TXAS)
• Prostacyclin synthase
• Microsomal PGE synthase
• 5-Lipoxygenase

Correct Answer: Thromboxane synthase (TXAS)

Q17. Formation of lipoxins commonly requires transcellular biosynthesis between which two cell types?

• Endothelial cells (12-LOX) and hepatocytes (5-LOX)
• Neutrophils (5-LOX) and platelets (12-LOX)
• Macrophages (COX-2) and red blood cells (15-LOX)
• Fibroblasts (COX-1) and lymphocytes (5-LOX)

Correct Answer: Neutrophils (5-LOX) and platelets (12-LOX)

Q18. Which structural feature is characteristic of the prostaglandin family (PGs)?

• A linear 20-carbon chain with no rings and a terminal alcohol
• A bicyclic steroid nucleus with 4 fused rings and a carboxylate
• A cyclopentane ring bearing hydroxyl group(s) and a terminal carboxylic acid on a 20-carbon backbone
• A glycerol backbone esterified to fatty acids

Correct Answer: A cyclopentane ring bearing hydroxyl group(s) and a terminal carboxylic acid on a 20-carbon backbone

Q19. Which drug specifically inhibits 5-lipoxygenase enzymatic activity and is used to reduce leukotriene synthesis?

• Montelukast
• Zileuton
• Ketoprofen
• Indomethacin

Correct Answer: Zileuton

Q20. The prolonged antiplatelet effect of low-dose aspirin is principally due to which pharmacological reason?

• Aspirin reversibly inhibits COX in megakaryocytes allowing rapid recovery
• Aspirin irreversibly acetylates platelet COX and platelets lack nucleus to resynthesize the enzyme
• Aspirin blocks thromboxane receptor (TP) on platelets competitively
• Aspirin increases PGI2 synthesis in platelets leading to lasting inhibition

Correct Answer: Aspirin irreversibly acetylates platelet COX and platelets lack nucleus to resynthesize the enzyme

Download