Production and damaging reactions of free radicals on lipids, proteins, carbohydrates, nucleic acids MCQs With Answer

Free radicals—reactive oxygen species (ROS) and reactive nitrogen species (RNS)—are produced endogenously (mitochondria, enzymatic systems) and exogenously (radiation, xenobiotics). Their chain reactions cause lipid peroxidation, protein oxidation, carbohydrate modification and nucleic acid damage, driving oxidative stress and disease. Key damaging products include malondialdehyde, 4-hydroxynonenal, protein carbonyls and 8-oxo‑2′‑deoxyguanosine; transition metals and Fenton chemistry amplify harm. Antioxidant defenses (SOD, catalase, glutathione peroxidase, vitamins) and repair systems limit injury. Understanding mechanisms, biomarkers, assays (TBARS, DNPH, Comet) and protective strategies is essential for B.Pharm students studying pharmacology, toxicology and drug design. This concise review emphasizes mechanisms, clinical implications and laboratory approaches relevant to drug development and therapeutics. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary initiating radical in classical lipid peroxidation?

• Superoxide anion (O2•−)
• Hydroxyl radical (•OH)
• Peroxyl radical (ROO•)
• Alkoxyl radical (RO•)

Correct Answer: Hydroxyl radical (•OH)

Q2. Which assay is commonly used to estimate malondialdehyde (MDA) as a marker of lipid peroxidation?

• DNPH carbonyl assay
• TBARS assay
• Comet assay
• ELISA for SOD

Correct Answer: TBARS assay

Q3. Which product is a reactive aldehyde formed during lipid peroxidation and can form protein adducts?

• 8-oxo-2′-deoxyguanosine (8-oxo-dG)
• 4-hydroxynonenal (4-HNE)
• Protein carbonyl
• Advanced glycation end-product (AGE)

Correct Answer: 4-hydroxynonenal (4-HNE)

Q4. The Fenton reaction generates hydroxyl radical from hydrogen peroxide in the presence of which ion?

• Calcium (Ca2+)
• Iron (Fe2+)
• Sodium (Na+)
• Magnesium (Mg2+)

Correct Answer: Iron (Fe2+)

Q5. Which enzyme catalyzes dismutation of superoxide anion to hydrogen peroxide and oxygen?

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

Correct Answer: Superoxide dismutase (SOD)

Q6. Protein oxidation commonly results in formation of which stable biomarker?

• Protein carbonyls
• Mitochondrial DNA deletions
• Lipid hydroperoxides
• 8-oxo-dG

Correct Answer: Protein carbonyls

Q7. Peroxynitrite (ONOO−) is formed by reaction between nitric oxide (NO•) and which radical?

• Hydroxyl radical (•OH)
• Superoxide anion (O2•−)
• Alkoxyl radical (RO•)
• Singlet oxygen (1O2)

Correct Answer: Superoxide anion (O2•−)

Q8. Oxidative damage to DNA producing 8-oxo-dG primarily affects which base?

• Adenine
• Cytosine
• Guanine
• Thymine

Correct Answer: Guanine

Q9. Which DNA repair pathway primarily removes oxidized bases like 8-oxo-dG?

• Base excision repair (BER)
• Nucleotide excision repair (NER)
• Mismatch repair (MMR)
• Homologous recombination (HR)

Correct Answer: Base excision repair (BER)

Q10. The Comet assay is used to detect which type of cellular damage?

• Protein carbonylation
• Lipid peroxidation
• DNA strand breaks and alkali-labile sites
• AGE cross-links

Correct Answer: DNA strand breaks and alkali-labile sites

Q11. Glutathione peroxidase reduces hydrogen peroxide using which cofactor or substrate?

• NADPH
• Glutathione (GSH)
• Vitamin C
• Thioredoxin

Correct Answer: Glutathione (GSH)

Q12. Which of the following best describes chain propagation step in lipid peroxidation?

• Initiation of lipid radical by •OH
• Peroxyl radical abstracts hydrogen from adjacent lipid forming new lipid radical
• Termination by combination of two radicals
• Repair of oxidized lipids by enzymes

Correct Answer: Peroxyl radical abstracts hydrogen from adjacent lipid forming new lipid radical

Q13. Advanced glycation end-products (AGEs) formed on carbohydrates and proteins contribute to damage by which mechanism?

• Direct DNA strand cleavage
• Cross-linking proteins and promoting inflammation
• Scavenging free radicals efficiently
• Stimulating catalase activity

Correct Answer: Cross-linking proteins and promoting inflammation

Q14. Which transition metal chelator is commonly used experimentally to inhibit Fenton chemistry?

• Deferoxamine
• EDTA at high concentrations
• Ascorbic acid
• Glutathione

Correct Answer: Deferoxamine

Q15. Which reactive species is most likely produced by neutrophil myeloperoxidase from hydrogen peroxide and chloride?

• Singlet oxygen
• Hypochlorous acid (HOCl)
• Peroxynitrite
• Hydroxyl radical

Correct Answer: Hypochlorous acid (HOCl)

Q16. Measurement of protein thiol oxidation often targets which amino acid residue?

• Lysine
• Cysteine
• Phenylalanine
• Proline

Correct Answer: Cysteine

Q17. Which antioxidant vitamin can regenerate vitamin E and acts as a reducing agent in aqueous compartments?

• Vitamin K
• Vitamin C (ascorbate)
• Vitamin A
• Vitamin D

Correct Answer: Vitamin C (ascorbate)

Q18. Which biomarker specifically indicates oxidative damage to DNA rather than lipids or proteins?

• Malondialdehyde (MDA)
• Protein carbonyls
• 8-oxo-2′-deoxyguanosine (8-oxo-dG)
• 4-hydroxynonenal (4-HNE)

Correct Answer: 8-oxo-2′-deoxyguanosine (8-oxo-dG)

Q19. Which of the following reactions describes Haber–Weiss chemistry overall (net conversion)?

• O2 + H2O → H2O2 + O2•−
• O2•− + H2O2 → O2 + •OH + OH−
• NO• + O2 → NO2
• H2O2 → H2O + 1/2 O2

Correct Answer: O2•− + H2O2 → O2 + •OH + OH−

Q20. Oxidative deamination of amino acids by ROS leads to which functional consequence on proteins?

• Increased enzymatic activity
• Formation of carbonyl groups and loss of function
• Glycosylation of lysine residues
• Phosphorylation of serine residues

Correct Answer: Formation of carbonyl groups and loss of function

Q21. Which enzyme family repairs oxidized pyrimidines and bulky adducts rather than small oxidized bases?

• Nucleotide excision repair (NER) enzymes
• Base excision repair (BER) enzymes
• DNA glycosylases specific for 8-oxo-dG
• Mismatch repair (MMR) proteins

Correct Answer: Nucleotide excision repair (NER) enzymes

Q22. Which technique directly detects protein carbonyl groups as a measure of protein oxidation?

• TBARS assay
• DNPH (dinitrophenylhydrazine) derivatization and spectrophotometry
• Comet assay
• ELISA for 8-oxo-dG

Correct Answer: DNPH (dinitrophenylhydrazine) derivatization and spectrophotometry

Q23. What is the effect of lipid peroxidation on membrane properties?

• Increased membrane fluidity and decreased permeability
• Decreased membrane fluidity and increased permeability
• No effect on membrane structure
• Instant membrane repair by peroxidases

Correct Answer: Decreased membrane fluidity and increased permeability

Q24. Which small-molecule antioxidant is a tripeptide that maintains intracellular redox balance?

• Ascorbic acid
• Glutathione (GSH)
• Alpha-tocopherol
• Uric acid

Correct Answer: Glutathione (GSH)

Q25. Which enzyme reduces lipid hydroperoxides within membranes using glutathione?

• Glutathione peroxidase 4 (GPx4)
• Catalase
• Superoxide dismutase
• Glutathione reductase

Correct Answer: Glutathione peroxidase 4 (GPx4)

Q26. Which oxidative modification to nucleic acids can cause GC → TA transversion mutations?

• Thymine glycol formation
• 8-oxo-2′-deoxyguanosine (8-oxo-dG) mispairing
• Uracil incorporation
• Interstrand cross-links

Correct Answer: 8-oxo-2′-deoxyguanosine (8-oxo-dG) mispairing

Q27. Which cellular organelle is the major endogenous source of ROS during aerobic metabolism?

• Golgi apparatus
• Mitochondria
• Peroxisomes exclusively
• Lysosomes only

Correct Answer: Mitochondria

Q28. Nitrosative stress often results in tyrosine modification forming which residue?

• Nitrotyrosine
• Phosphotyrosine
• S-nitrosocysteine
• Hydroxyproline

Correct Answer: Nitrotyrosine

Q29. Which cellular antioxidant enzyme catalyzes decomposition of hydrogen peroxide to water and oxygen?

• Catalase
• Glutathione peroxidase
• Superoxide dismutase
• Monoamine oxidase

Correct Answer: Catalase

Q30. In the context of drug-induced oxidative stress, which strategy is best for reducing radical-mediated macromolecule damage?

• Inhibition of DNA repair enzymes
• Enhancing antioxidant defenses and metal chelation
• Increasing transition metal availability
• Suppressing glutathione synthesis

Correct Answer: Enhancing antioxidant defenses and metal chelation

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