- The following statements refer to the E. coli replicative DNA polymerase:
(A) DNA POI I displays very limited processivity and possesses 3’à5′ exonuclease activity, allowing fidelity of DNA replication.
(B) DNA POI III is suitable for leading strand DNA synthesis due to its high processivity and 5à3′ exonuclease activity that removes incorrect nucleotides incorporated during DNA synthesis.
(C) DNA POI I possesses 5à3′ exonuclease activity which allows removal of the RNA primer while its 3′ polymerase activity allows it to fill the gap created by removal of the RNA primer
(D) DNA POI III is suitable for lagging strand DNA synthesis due to its low processivity and 5’à3′ exonuclease activity.
Which one of the options below represents the combination of all correct statements?
(1) D only (2) B and C
(3) A and B (4) A and C
Analysis of Each Statement
(A) DNA Pol I displays very limited processivity and possesses 3′→5′ exonuclease activity, allowing fidelity of DNA replication.
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True: DNA polymerase I has limited processivity compared to Pol III and possesses 3′→5′ exonuclease proofreading activity that enhances fidelity during DNA synthesis.
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However, its processivity is low, making it unsuitable for bulk replication.
(B) DNA Pol III is suitable for leading strand DNA synthesis due to its high processivity and 5′→3′ exonuclease activity that removes incorrect nucleotides incorporated during DNA synthesis.
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Partially incorrect: DNA polymerase III is highly processive and suitable for leading strand synthesis.
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However, the proofreading exonuclease activity is 3′→5′, not 5′→3′. The 5′→3′ exonuclease activity is characteristic of Pol I, not Pol III.
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Pol III lacks 5′→3′ exonuclease activity.
(C) DNA Pol I possesses 5′→3′ exonuclease activity which allows removal of the RNA primer while its 3′ polymerase activity allows it to fill the gap created by removal of the RNA primer.
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True: DNA polymerase I uniquely has 5′→3′ exonuclease activity to remove RNA primers and 5′→3′ polymerase activity to fill in the gaps with DNA.
(D) DNA Pol III is suitable for lagging strand DNA synthesis due to its low processivity and 5′→3′ exonuclease activity.
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False: DNA polymerase III has high processivity, essential for lagging strand synthesis.
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It also lacks 5′→3′ exonuclease activity; this activity is present in Pol I.
Summary Table
| Statement | Correctness | Explanation |
|---|---|---|
| A | Correct | Pol I has limited processivity and 3′→5′ exonuclease proofreading activity. |
| B | Incorrect | Pol III is highly processive but does not have 5′→3′ exonuclease activity; proofreading is 3′→5′. |
| C | Correct | Pol I removes RNA primers via 5′→3′ exonuclease and fills gaps with polymerase activity. |
| D | Incorrect | Pol III has high processivity and lacks 5′→3′ exonuclease activity. |
Correct Combination of Statements
(4) A and C
Explanation
-
DNA polymerase I is specialized for primer removal and gap filling with limited processivity but has proofreading ability.
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DNA polymerase III is the main replicative polymerase with high processivity and 3′→5′ exonuclease proofreading activity but lacks 5′→3′ exonuclease activity.
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The 5′→3′ exonuclease activity for primer removal is unique to DNA polymerase I.
Keywords
E. coli DNA polymerase I, DNA polymerase III, processivity, exonuclease activity, 3′→5′ proofreading, 5′→3′ exonuclease, leading strand synthesis, lagging strand synthesis, RNA primer removal, Okazaki fragments
Final Answer:
(4) A and C
21 Comments
Manisha choudhary
July 29, 2025Done sir 👍🏻
Surbhi Rajawat
July 29, 2025Options A and C are correct.
Priya Khandal
July 29, 2025Done sir a and c
Priti Khandal
July 29, 2025Done sir Option 4 is right because polymerase 1 ke pass 3 5 proof reading activity present hoti hai and primer remove bhi karta h
Ankita Pareek
July 30, 2025Poly1 has both 5′-3′ exonuclease activity as well as polymerase activity so that it can fill the gap by polymerase activity and remove the primers by 5′-3′ exonuclease activity
Poly 3 has hi processivity lack 5′-3’exonuclease activity
Sneha Kumawat
July 30, 20254 th is correct pol 1 limited processivity and 3’tp 5 ‘ exonuclease activity and pol 1 possesses 5′ to 3’ exonucleus activity to remove primer
Khushi Agarwal
July 30, 2025Correct answer is 4th
A and c are correct pol 3 has high processivity and lack of 5′-3′ exon. Proofreading
Khushi Vaishnav
July 30, 2025Statement A and C are correct
Vanshika Sharma
July 30, 2025Statement a and c are correct
Anisha jakhar
July 30, 2025A and C are the correct statements
shruti sharma
July 30, 2025A and C IS CORRECT
Santosh Saini
July 31, 2025Statement A and C are correct
Soniya Shekhawat
July 31, 2025The 5′→3′ exonuclease activity for primer removal is present in dna pol 1 and DNA polymerase 3 Have high processivity and 3’to5′ exonuclease Proofreading activity so Aand C is correct
Aafreen
July 31, 2025Ans-4 A and C statement is correct
Kajal
July 31, 2025Option A and c is right
Diksha Chhipa
July 31, 2025A and c are correct because dna pol 1 have less processvity than dna pol3 and dna pol 1 have 5to 3 prime exonuclease activity which used in rna primer removing and gap filling
Dharmpal Swami
August 1, 2025A&C are write
Mahima Sharma
August 3, 2025❓🫤
Varsha Tatla
August 3, 2025Correct combination of statement a,c
Deepika sheoran
August 3, 2025Option 4th is correct answer
Because 5’_3′ exonuclease proof reading Activity .
Polymerase remove Rna primer 5’_3′ exonuclease &fill gaps with polymerase Activity.
Deepika Sheoran
November 7, 2025Option 4 th is correct A and C