Cytogenetics Questions and Answers – Repair of DNA Damage: MMR, BER – 2

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This set of Cytogenetics Quiz focuses on “Repair of DNA Damage: MMR, BER – 2”.

1. Which of the following is not a function of APE1?
a) 5’->3’ exonuclease
b) Generating nick at 5’ end
c) Generating abasic site
d) Improving fidelity of pol beta
View Answer

Answer: c
Explanation: While APE1 has a 5’-> 3’ exonuclease activity, it is not a bifunctional glycosylase and can’t generate an abasic site.
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2. Which of the DNA polymerase in prokaryotes is responsible for re-synthesizing the stretch in MMR?
a) DNA polymerase Beta
b) DNA polymerase I
c) DNA polymerase II
d) DNA polymerase III
View Answer

Answer: d
Explanation: Polymerase III is responsible for re-synthesizing the stretch of DNA in MMR between the nick made my Mut H and the mis paired base.

3. GATC sequence on either side of the mismatch can help in MMR.
a) True
b) False
View Answer

Answer: a
Explanation: Mut H binds to hemimethylated GATC sequences, and such sequences on either side of the mismatch can help in MMR. Although even a GATC 1000bp away can help determine the correct stand to cut, it efficiency reduces with increasing distance.
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4. Which DNA polymerase plays a role in repair synthesis in BER in prokaryotes?
a) Pol I
b) Pol II
c) Pol III
d) Pol IV
View Answer

Answer: a
Explanation: While pol III is responsible for the repair synthesis in MMR, pol I is however responsible for repair synthesis in BER in prokaryotes.

5. BER detects wrong bases by __________________
a) Bulges produced in the DNA
b) Strength of bond between the bases
c) Flipping of bases
d) Detected by RNA polymerase stalling
View Answer

Answer: c
Explanation: It has been seen that mis-incorporated bases have a tendency to appear flipped out, these flipped out bases are recognized by the BER. This is because flipping requires less energy than distortions like bulging. RNA pol stalling can trigger NER mainly TC-NER.
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6. AP endonuclease can cleave the DNA at__________ while AP lyase will cleave the DNA at__________
a) 5’, 3’
b) 3’, 3’
c) 3’, 5’
d) 5’, 5’
View Answer

Answer: a
Explanation: The AP endonuclease can cleave at the 5’ end of the Apurinic or Apyrimidine site, while the bifunctional AP lyase cleaves at the 3’ end.

7. Which of the following can’t be repaired by BER?
a) Abasic sites
b) Deamination
c) CPD
d) Oxidative damage
View Answer

Answer: c
Explanation: BER usually deals with single base damages, and NER takes care of the damages involving bulky lesions like CPD. Abasic site generation is the 1st step of BER process so it can carry out the reaction easily.
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8. Which of the bond in the nucleotide is broken 1st in BER?
a) Bond between two consequent bases
b) Bond between base and sugar
c) Bond between base and phosphate
d) Bond between two complementary bases
View Answer

Answer: b
Explanation: The glycosidic bond between the sugar residue and the nitrogenous base is the 1st to be broken by BER glycosylases generating an abasic site.

9. Which of the following will be seen to resolve the flap in eukaryotic short patch BER?
a) dRPases
b) FEN1
c) Pol Beta
d) APE1
View Answer

Answer: c
Explanation: In eukaryotes, there is no requirement of a phosphodiesterase to resolve the short flap generated by short patch BER. It is taken care of by pol beta.
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10. Which factor works in conjugation with FEN1?
a) XRCC
b) PCNA
c) Pol beta
d) RPA
View Answer

Answer: b
Explanation: PCNA or the beta clamp analogue in eukaryotes assists the FEN1 to cleave the long flap generated by long patch BER. This can’t be taken care of by the pol beta alone.

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