Molecular Biology Multiple Choice Questions on “Chemical Mutagens Damage DNA”.
1. Which base undergoes spontaneous damage under physiological conditions?
A. Thymine
B. Cytosine
C. Uracil
D. Guanine
Answer: B
Explanation: The most frequent and important kind of hydrolytic damage is deamination of the base cytosine. Under normal physiological conditions, cytosine undergoes deamination thereby generating the unnatural base uracil.
2. With which base uracil pairs in the opposite strand upon replication?
A. Adenine
B. Guanine
C. Cytosine
D. Thymine
Answer: A
Explanation: Uracil preferentially pairs with adenine and thus introduces that base in the opposite strand upon replication. This uracil is generated by the deamination of cytosine.
3. Which base is generated due to the deamination of adenine?
A. Guanine
B. Cytosine
C. Uracil
D. Hypoxanthine
Answer: D
Explanation: Deamination converts adenine to hypoxanthine. Hypoxanthine forms a hydrogen bond to cytosine rather than to thymine.
4. Which base is generated by the deamination of guanine?
A. Xanthine
B. Cytosine
C. Hypoxanthine
D. Thymine
Answer: A
Explanation: Deamination converts guanine to Xanthine. Xanthine forms a hydrogen bond to cytosine.
5. Bases in the mRNA undergo depurination.
A. True
B. False
Answer: B
Explanation: mRNA does not undergo depurination where as DNA does. DNA undergoes depurination by spontaneous hydrolysis of the N-glycosyl linkage, and this produces and abasic site in the DNA.
6. In vertebrate DNA, which base is frequently present in place of cytosine on which methyl transferase acts?
A. Hypoxanthine
B. 5-methylcytosine
C. Xanthine
D. Adenine
Answer: B
Explanation: Vertebrate DNA frequently contains 5-methylcytosine in place of cytosine. This base has a role in transcriptional silencing.
7. Which base is generated by the deamination of 5-methylcytosine?
A. Thymine
B. Adenine
C. Guanine
D. Uracil
Answer: A
Explanation: Deamination of 5-methylcytosine generates thymine. This thymine pairs with the thymine in the next round of replication.
8. Which laboratory mutagen is prone to mutation of DNA?
A. N-methyl, N1-nitro, N-nitrosoguanidine
B. N-methyl, N2-nitro, N-nitrosoguanidine
C. N1-methyl, N1-nitro, N-nitrosoguanidine
D. N-methyl, N-nitro, N-nitrosoguanidine
Answer: A
Explanation: DNA is vulnerable to damage from adenylation, oxidation and radiation. The most potent laboratory mutagen is N-methyl, N1-nitro, N-nitrosoguanidine.
9. Which site of guanine is the site for mutation?
A. C-4
B. C-6
C. C-1
D. C-2
Answer: B
Explanation: The most vulnerable site of alkylation is the keto-group of carbon atom 6 of the guanine residue. The product of this alkylation is C6-methyl guanine.
10. What is the product by mutation by oxidation of DNA?
A. 2,7-dihydro-8-oxoguanine
B. 1,7-dihydro-7-oxoguanine
C. 7,8-dihydro-8-oxoguanine
D. 7,4-dihydro-8-oxoguanine
Answer: C
Explanation: The potent oxidizing agents are generated by ionizing radiation and by chemical agents that generate free radicals. Oxidation of guanine generates 7,8-dihydro-8-oxoguanine.
11. To which base OXOG base pairs?
A. A, C
B. A, G
C. G, C
D. A, T
Answer: A
Explanation: The OXOG highly base pairs with adenine as well as cytosine. In the second round of replication of gives rise to a G : C to T : A transversion.
12. In the case of thymine dimer which type of ring compound is formed?
A. Cyclohexane
B. Cyclobutane
C. Cyclopropane
D. Cycloheptane
Answer: B
Explanation: The bonding of two thymine bases generates thymine dimer. This comprises a cyclobutane ring generated by links between carbon atom 5 and carbon atom 6 of thymine.
13. 5-bromouracil is the analog of which base?
A. Thymine
B. Guanine
C. Cytosine
D. Uracil
Answer: A
Explanation: 5-bromouracil is the analog of thymine. This substitution allows the base to mispair with guanine via the enol-tautomer.
14. Bleomycin is the anticancer agent.
A. True
B. False
Answer: A
Explanation: Bleomycin acts as an anticancer agent which causes breaks in the DNA of the cancer cells. Those agents that cause the DNA to break are said to be as clastogenic agents.
15. In the following compound which is one of the intercalating agents?
A. Ethidium
B. 5-bromouracil
C. Purine
D. Clastrogen
Answer: A