Free radicals pharmacology: generation and biological roles MCQs With Answer

Free radicals pharmacology: generation and biological roles MCQs With Answer

This quiz collection addresses generation, chemistry, biological roles and pharmacological modulation of free radicals and reactive oxygen/nitrogen species (ROS/RNS) for M.Pharm students. Questions cover enzymatic and non-enzymatic sources (mitochondria, NADPH oxidase, xanthine oxidase, cytochrome P450), key radical species (superoxide, hydroxyl, hydrogen peroxide, peroxynitrite), major reaction pathways (Fenton, Haber–Weiss), oxidative damage mechanisms (lipid peroxidation, protein/DNA oxidation), measurement techniques (EPR, DCFH-DA, isoprostanes) and therapeutic strategies (antioxidants, metal chelators, enzyme inhibitors, Nrf2 activators). Designed at an advanced level, the MCQs test mechanistic understanding and pharmacological implications in disease and drug development.

Q1. Which of the following is the primary enzymatic source of superoxide anion (O2•−) during the phagocytic oxidative burst?

• NADPH oxidase (NOX2)
• Mitochondrial complex I
• Xanthine oxidase
• Cytochrome P450

Correct Answer: NADPH oxidase (NOX2)

Q2. The Fenton reaction describes formation of the highly reactive hydroxyl radical (•OH) from hydrogen peroxide in the presence of which metal ion?

• Iron (Fe2+)
• Copper (Cu2+)
• Zinc (Zn2+)
• Magnesium (Mg2+)

Correct Answer: Iron (Fe2+)

Q3. Peroxynitrite (ONOO−) is formed by the rapid reaction between which two species?

• Nitric oxide (NO•) and superoxide (O2•−)
• Hydrogen peroxide (H2O2) and hydroxyl radical (•OH)
• Singlet oxygen (1O2) and hydrogen peroxide (H2O2)
• Nitrite (NO2−) and hydrogen peroxide (H2O2)

Correct Answer: Nitric oxide (NO•) and superoxide (O2•−)

Q4. Which antioxidant enzyme catalyzes the dismutation of superoxide into hydrogen peroxide and molecular oxygen?

• Superoxide dismutase (SOD)
• Catalase
• Glutathione peroxidase (GPx)
• Peroxiredoxin

Correct Answer: Superoxide dismutase (SOD)

Q5. Glutathione peroxidase requires which cofactor to reduce hydrogen peroxide to water?

• Reduced glutathione (GSH)
• NADPH
• Iron-sulfur cluster
• Vitamin C (ascorbate)

Correct Answer: Reduced glutathione (GSH)

Q6. Which reaction pair describes the Haber–Weiss sequence often invoked in biological oxidative stress?

• Superoxide reduces ferric iron to ferrous; ferrous iron reacts with H2O2 to produce •OH (net Haber–Weiss/Fenton chemistry)
• Hydrogen peroxide is converted to water by catalase; superoxide is converted to oxygen by SOD
• Nitric oxide reacts with oxygen to form nitrogen dioxide which then oxidizes lipids
• Singlet oxygen formation from excited chlorophyll in photosynthetic tissues

Correct Answer: Superoxide reduces ferric iron to ferrous; ferrous iron reacts with H2O2 to produce •OH (net Haber–Weiss/Fenton chemistry)

Q7. Which of the following is a widely used iron chelator that can limit hydroxyl radical production in experimental or clinical settings?

• Deferoxamine
• Allopurinol
• Edaravone
• Tempol

Correct Answer: Deferoxamine

Q8. Xanthine oxidase contributes to ROS formation particularly during ischemia–reperfusion by oxidizing hypoxanthine to xanthine and producing which species?

• Superoxide (O2•−)
• Hydroxyl radical (•OH)
• Singlet oxygen (1O2)
• Peroxynitrite (ONOO−)

Correct Answer: Superoxide (O2•−)

Q9. Which of these pharmacological agents directly inhibits xanthine oxidase and is used to reduce ROS-mediated injury in gout and ischemia models?

• Allopurinol
• N-acetylcysteine (NAC)
• Deferoxamine
• Vitamin E (α-tocopherol)

Correct Answer: Allopurinol

Q10. Electron paramagnetic resonance (EPR) spin trapping is the most specific method for detecting which of the following?

• Short-lived free radical species (e.g., •OH, O2•−)
• Total antioxidant capacity of plasma
• Levels of malondialdehyde by TBARS assay
• 8-OHdG as a marker of DNA oxidation

Correct Answer: Short-lived free radical species (e.g., •OH, O2•−)

Q11. Lipid peroxidation chain propagation is primarily initiated by which radical attacking a polyunsaturated fatty acid?

• Hydroxyl radical (•OH)
• Nitric oxide (NO•)
• Singlet oxygen (1O2)
• Hydrogen peroxide (H2O2)

Correct Answer: Hydroxyl radical (•OH)

Q12. Which biomarker is considered a sensitive and specific indicator of oxidative damage to DNA?

• 8-hydroxy-2′-deoxyguanosine (8-OHdG)
• Malondialdehyde (MDA)
• Protein carbonyls
• Isoprostanes

Correct Answer: 8-hydroxy-2′-deoxyguanosine (8-OHdG)

Q13. Nitric oxide synthase (NOS) uncoupling in endothelial cells shifts NO production toward superoxide generation. Which cofactor deficiency contributes to NOS uncoupling?

• Tetrahydrobiopterin (BH4)
• Flavin adenine dinucleotide (FAD)
• Iron-sulfur cluster
• NADH

Correct Answer: Tetrahydrobiopterin (BH4)

Q14. Which drug is a clinically used free radical scavenger approved for acute ischemic stroke in some countries and acts by trapping hydroxyl radicals?

• Edaravone
• N-acetylcysteine (NAC)
• Deferoxamine
• Apocynin

Correct Answer: Edaravone

Q15. Activation of the Nrf2 pathway provides cytoprotection mainly by upregulating genes encoding which of the following?

• Antioxidant and phase II detoxifying enzymes (e.g., HO-1, GST, GCL)
• Mitochondrial electron transport chain proteins
• Pro-inflammatory cytokines
• Matrix metalloproteinases

Correct Answer: Antioxidant and phase II detoxifying enzymes (e.g., HO-1, GST, GCL)

Q16. In the context of ROS biology, why are mitochondria considered both major sources and targets of oxidative stress?

• Electron leakage from complexes I and III generates ROS, and mitochondrial membranes and mtDNA are susceptible to oxidative damage impairing respiration
• Mitochondria produce only hydrogen peroxide which is harmless to their components
• Mitochondria synthesize all cellular antioxidant enzymes, making them immune to ROS
• Mitochondria export ROS to lysosomes where they are neutralized

Correct Answer: Electron leakage from complexes I and III generates ROS, and mitochondrial membranes and mtDNA are susceptible to oxidative damage impairing respiration

Q17. Which intracellular thiol is central to redox buffering and is required for glutathione peroxidase activity and detoxification reactions?

• Glutathione (GSH)
• Thioredoxin
• Cysteine protease
• Coenzyme A

Correct Answer: Glutathione (GSH)

Q18. Tempol is an example of a pharmacological agent described as a:

• Membrane-permeable SOD mimetic and redox-cycling nitroxide
• Specific inhibitor of NADPH oxidase subunit p47phox
• Iron chelator that blocks Fenton chemistry
• Selective inhibitor of inducible NOS (iNOS)

Correct Answer: Membrane-permeable SOD mimetic and redox-cycling nitroxide

Q19. Which pathological process is most directly linked to oxLDL (oxidized low-density lipoprotein) and ROS-mediated endothelial dysfunction?

• Atherosclerosis
• Parkinson’s disease
• Type I diabetes mellitus
• Osteoarthritis

Correct Answer: Atherosclerosis

Q20. The dichotomous role of ROS in cells includes physiological signaling and pathological damage. Which of the following best exemplifies a physiological ROS signaling role?

• Redox-dependent modulation of protein tyrosine phosphatases during growth factor signaling
• Lipid peroxidation-mediated cell membrane rupture during necrosis
• DNA strand breaks leading to mutagenesis
• Protein carbonylation causing proteasomal degradation

Correct Answer: Redox-dependent modulation of protein tyrosine phosphatases during growth factor signaling

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