4.5 Mutagens, Base Analogs & DNA Repair — Test 2

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4.5 Mutagens, Base Analogs & DNA Repair — Test 2

Q1. X-rays and gamma rays act as:✓ High-energy physical mutagens

Q2. Which of the following is a particulate (corpuscular) radiation?✓ Alpha particles

Q3. Thymine-thymine (T-T) dimers are formed mainly by:✓ Non-ionising (ultraviolet) radiation

Q4. 5-Bromouracil is a base analog of:✓ Thymine

Q5. 2-Aminopurine, a mutagenic base analog, resembles and substitutes for:✓ Adenine

Q6. The formation of 7-ethylguanine in DNA is caused by an:✓ Alkylating agent

Q7. Ethyl methanesulfonate (EMS) and nitrogen mustard are examples of which class of mutagen?✓ Alkylating agents

Q8. Treatment of cytosine with nitrous acid (HNO₂) converts it to:✓ Uracil

Q9. Deamination of adenine (e.g. by nitrous acid) produces:✓ Hypoxanthine

Q10. Acridine dyes (e.g. proflavine) cause mutations by:✓ Intercalating between bases, causing insertions/deletions (frameshifts)

Q11. Thymine dimers in bacteria can be directly reversed by:✓ Photoreactivation (photolyase)

Q12. Bulky lesions such as pyrimidine dimers are removed (in the dark) mainly by:✓ Nucleotide excision repair

Q13. A single damaged or incorrect base (e.g. uracil in DNA) is removed by:✓ Base excision repair (via a DNA glycosylase)

Q14. Errors that escape proofreading during replication are corrected by:✓ Mismatch repair

Q15. The Ames test uses bacteria to detect whether a chemical is a:✓ Mutagen (and potential carcinogen)

Q16. A likely cellular response of a damaged cell to ionising radiation is:✓ Cell-cycle (growth) arrest to allow repair

Q17. Ultraviolet (UV) light damages DNA principally by forming:✓ Pyrimidine (e.g. thymine) dimers

Q18. Xeroderma pigmentosum, a disorder of extreme UV sensitivity, results from a defect in:✓ Nucleotide excision repair

Q19. Which agent causes mutations by being mistakenly incorporated into DNA in place of a normal base?✓ A base analog (e.g. 5-bromouracil)

Q20. Match each mutagen with its mechanism and select the correct option.✓ A-ii, B-i, C-iv, D-iii