DNA functioning and replication MCQs With Answer

Introduction: DNA functioning and replication MCQs With Answer is designed for B. Pharm students to reinforce core concepts of DNA structure, replication mechanisms, enzymology, and pharmacological targets. This resource covers DNA replication, semiconservative replication, replication fork dynamics, DNA polymerases, helicase, primase, ligase, Okazaki fragments, proofreading, mismatch repair, telomerase, and replication inhibitors like quinolones and topoisomerase inhibitors. Emphasis is on replication fidelity, replication licensing (MCM), sliding clamps (PCNA), and drug interactions relevant to pharmacology. Clear explanations and targeted multiple-choice questions enhance clinical and pharmaceutical understanding of molecular mechanisms and drug actions. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which classic experiment provided direct evidence for semiconservative DNA replication?

• Meselson-Stahl experiment
• Hershey-Chase experiment
• Avery-MacLeod-McCarty experiment
• Watson-Crick model proposal

Correct Answer: Meselson-Stahl experiment

Q2. Which enzyme unwinds the DNA double helix at the replication fork?

• DNA ligase
• Helicase
• DNA polymerase
• Topoisomerase

Correct Answer: Helicase

Q3. Which enzyme synthesizes the short RNA primer needed to initiate DNA synthesis?

• Primase
• DNA polymerase I
• DNA ligase
• Topoisomerase II

Correct Answer: Primase

Q4. DNA polymerases synthesize DNA in which direction and proofread using which exonuclease activity?

• 3’→5′ synthesis; 5’→3′ proofreading
• 5’→3′ synthesis; 3’→5′ proofreading
• 5’→3′ synthesis; 5’→3′ proofreading
• 3’→5′ synthesis; 3’→5′ proofreading

Correct Answer: 5’→3′ synthesis; 3’→5′ proofreading

Q5. Which strand of DNA is synthesized discontinuously, producing Okazaki fragments?

• Leading strand
• Lagging strand
• Both strands continuously
• Neither strand is synthesized discontinuously

Correct Answer: Lagging strand

Q6. Which enzyme joins Okazaki fragments into a continuous DNA strand?

• DNA polymerase III
• DNA ligase
• Primase
• Helicase

Correct Answer: DNA ligase

Q7. What is the primary replicative DNA polymerase in bacteria responsible for high-processivity synthesis?

• DNA polymerase I
• DNA polymerase II
• DNA polymerase III
• DNA polymerase IV

Correct Answer: DNA polymerase III

Q8. Which enzyme in prokaryotes removes RNA primers using its 5’→3′ exonuclease activity?

• DNA polymerase III
• DNA polymerase I
• RNase H
• DNA ligase

Correct Answer: DNA polymerase I

Q9. How does DNA replication initiate at origins in bacteria and many eukaryotic chromosomes?

• Unidirectional replication from multiple dispersed points
• Bidirectional replication from a defined origin
• Replication from telomeres only
• Random initiation anywhere without origins

Correct Answer: Bidirectional replication from a defined origin

Q10. Which enzyme extends telomeres using an RNA template and has reverse transcriptase activity?

• Telomerase
• Topoisomerase I
• DNA polymerase δ
• RNA polymerase II

Correct Answer: Telomerase

Q11. Which bacterial enzyme introduces negative supercoils and is the target of fluoroquinolone antibiotics?

• Topoisomerase I
• DNA gyrase (topoisomerase II)
• Helicase
• Primase

Correct Answer: DNA gyrase (topoisomerase II)

Q12. Fluoroquinolones exert antibacterial action primarily by inhibiting which process?

• RNA transcription by RNA polymerase
• DNA gyrase-mediated DNA supercoiling
• Peptidoglycan cross-linking
• Protein synthesis at the ribosome

Correct Answer: DNA gyrase-mediated DNA supercoiling

Q13. Which eukaryotic DNA polymerase primarily synthesizes the leading strand during replication?

• DNA polymerase α
• DNA polymerase β
• DNA polymerase δ
• DNA polymerase ε

Correct Answer: DNA polymerase ε

Q14. What is the name of the sliding clamp protein that increases processivity in eukaryotic DNA replication?

• SSB
• PCNA
• RFC
• MCM

Correct Answer: PCNA

Q15. Which complex is loaded onto origins to license DNA replication and functions as the replicative helicase?

• RFC complex
• MCM complex
• PCNA complex
• RPA complex

Correct Answer: MCM complex

Q16. Which protein stabilizes single-stranded DNA at the replication fork in bacteria?

• RPA (replication protein A)
• SSB (single-stranded DNA-binding protein)
• PCNA
• DNA ligase

Correct Answer: SSB (single-stranded DNA-binding protein)

Q17. In the Meselson–Stahl experiment, which heavy isotope of nitrogen was used to label parental DNA?

• Nitrogen-14 (14N)
• Nitrogen-15 (15N)
• Carbon-14 (14C)
• Oxygen-18 (18O)

Correct Answer: Nitrogen-15 (15N)

Q18. DNA polymerases require which chemical group on a primer to add new nucleotides?

• 5′ phosphate group
• 3′ hydroxyl group
• 2′ hydroxyl group
• 3′ phosphate group

Correct Answer: 3′ hydroxyl group

Q19. Typical Okazaki fragment length in eukaryotic cells is approximately:

• 1000–2000 nucleotides
• 100–200 nucleotides
• 10–50 nucleotides
• 3000–5000 nucleotides

Correct Answer: 100–200 nucleotides

Q20. Which cofactor is used by many bacterial DNA ligases to seal nicks in DNA?

• ATP
• NAD+
• GTP
• FAD

Correct Answer: NAD+

Q21. Which repair system corrects base–base mismatches that escape proofreading after DNA replication?

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

Correct Answer: Mismatch repair (MMR)

Q22. Camptothecin and its derivatives act as anticancer agents by inhibiting which enzyme?

• Topoisomerase I
• Topoisomerase II
• DNA polymerase α
• Telomerase

Correct Answer: Topoisomerase I

Q23. Which nucleoside analog is a thymidine analog used as a chain terminator in anti-HIV therapy?

• Acyclovir
• Zidovudine (AZT)
• Ribavirin
• Ganciclovir

Correct Answer: Zidovudine (AZT)

Q24. Which protein complex functions as the clamp loader to place PCNA around DNA in eukaryotes?

• RFC (replication factor C)
• MCM complex
• RPA complex
• SSB protein

Correct Answer: RFC (replication factor C)

Q25. Which bacterial enzyme has both polymerase and 5’→3′ exonuclease activities important for primer removal and gap filling?

• DNA polymerase III
• DNA polymerase I
• DNA ligase
• RNase H

Correct Answer: DNA polymerase I

Q26. Which DNA repair pathway primarily removes bulky helix-distorting lesions such as UV-induced thymine dimers?

• Base excision repair (BER)
• Nucleotide excision repair (NER)
• Mismatch repair (MMR)
• Non-homologous end joining (NHEJ)

Correct Answer: Nucleotide excision repair (NER)

Q27. The model describing continuous synthesis on one strand and discontinuous synthesis on the other is termed:

• Conservative replication
• Dispersive replication
• Semidiscontinuous replication
• Rolling circle replication

Correct Answer: Semidiscontinuous replication

Q28. In eukaryotes, which polymerase-associated activity primes DNA synthesis and is part of the Pol α complex?

• DNA ligase activity
• Primase (RNA primer synthesis)
• Topoisomerase activity
• Proofreading exonuclease activity

Correct Answer: Primase (RNA primer synthesis)

Q29. Which eukaryotic DNA polymerase is primarily responsible for lagging-strand synthesis and has 3’→5′ proofreading?

• DNA polymerase α
• DNA polymerase β
• DNA polymerase δ
• DNA polymerase ε

Correct Answer: DNA polymerase δ

Q30. Which thymidine analog is commonly used to label newly synthesized DNA in replication studies?

• AZT (zidovudine)
• BrdU (bromodeoxyuridine)
• 5-FU (5-fluorouracil)
• Acyclovir

Correct Answer: BrdU (bromodeoxyuridine)

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