9. Which statement is correct regarding functioning of topoisomerase II?
(1) Separate double stranded DNA
(2) Act as primer
(3) Renature the SS DNA
(4) Attach to super coiled DNA and relax it
Introduction
Topoisomerase II is a vital enzyme that manages DNA topology during crucial cellular processes such as DNA replication, transcription, and chromosome segregation. Unlike topoisomerase I, which cuts one strand of DNA, topoisomerase II transiently cleaves both strands of the DNA helix to relieve supercoiling and untangle intertwined DNA molecules. This article explains the correct functioning of topoisomerase II and clarifies its role in relaxing supercoiled DNA.
How Does Topoisomerase II Function?
-
Double-Strand Breaks:
Topoisomerase II binds to DNA and introduces a transient double-stranded break in one segment of the DNA helix (called the G-segment or gate segment). -
Strand Passage:
It then passes another segment of double-stranded DNA (the T-segment) through this break. -
Resealing:
After passage, the enzyme reseals the break, restoring the integrity of the DNA. -
ATP Dependence:
This reaction requires ATP hydrolysis, which drives conformational changes in the enzyme necessary for strand passage and resetting the enzyme for another catalytic cycle. -
Relaxation of Supercoils:
By cutting and passing DNA strands through one another, topoisomerase II removes positive or negative supercoils, decatenates linked DNA circles, and resolves knots, thereby relaxing DNA and facilitating replication and transcription.
Why Option (4) Is Correct: “Attach to Supercoiled DNA and Relax It”
-
Topoisomerase II attaches to supercoiled DNA to relieve torsional stress.
-
It does so by cutting both strands, passing another DNA segment through, and then rejoining the strands.
-
This process relaxes supercoiling and resolves DNA tangles.
Why Other Options Are Incorrect
| Option | Description | Correctness & Explanation |
|---|---|---|
| (1) | Separate double stranded DNA | Incorrect: Topoisomerase II transiently cuts but does not permanently separate strands |
| (2) | Act as primer | Incorrect: Primers are RNA molecules synthesized by primase, not topoisomerase |
| (3) | Renature the SS DNA | Incorrect: Topoisomerase II does not renature single-stranded DNA; it modifies DNA topology |
Summary Table of Topoisomerase II Functions
| Function | Description |
|---|---|
| DNA Binding | Binds to supercoiled or tangled DNA |
| Double-Strand Break | Creates transient double-strand breaks |
| Strand Passage | Passes another DNA segment through the break |
| Resealing | Seals the DNA breaks to restore integrity |
| ATP Hydrolysis | Provides energy for conformational changes |
| DNA Relaxation and Decatenation | Removes supercoils and untangles DNA |
Conclusion
Topoisomerase II plays a critical role in managing DNA supercoiling by attaching to supercoiled DNA, introducing transient double-strand breaks, passing DNA segments through the break, and resealing the DNA. This mechanism relaxes supercoiled DNA and is essential for proper DNA replication and transcription. Therefore, the correct statement about topoisomerase II function is:
Answer:
(4) Attach to supercoiled DNA and relax it
30 Comments
Manisha choudhary
July 25, 2025Phli baar pta chla h topoisomer 1 and 2 m difference wow 🔥🔥
Diksha chhipa
July 29, 2025Topoisomerase 2 bind with supercoil dna and break the strand then strand passage and resealing the both strand. after atp hydrolysis dna become in relax state
Mansukh Kapoor
July 29, 2025The correct answer is TOPOISOMERASE 2 because it attach the supercoiled DNA and relax it in it’s orginal condition
Khushi Agarwal
July 29, 2025Option 4 is correct answer
Topoisomerase cut the both strands of Dna and remove twisting and then again joining the both strands
anurag giri
July 29, 2025Ans 4 Topoisomerase II mamage DNA supercoiling by attaching to supercoiled DNA, and breks bonds and passing DNA segments through the break, and resealing the DNA. This mechanism relaxes supercoiled DNA
Vanshika Sharma
July 29, 2025Ans is 4 topoisomerase 2 bcz it relaxes the supercoiled dna
Surbhi Rajawat
July 29, 2025Topoisomerase primarily works to relieve supercoiling that occurs in DNA due to helical unwinding. Therefore answer is 4
HIMANI FAUJDAR
July 29, 2025Topoisomerase bind with supercooled DNA and relax it so answer is 4
Heena
July 29, 2025Topoisomerase II relieves supercoiling produced due to activity of helicase enzyme
shruti sharma
July 29, 2025attach to super coiled DNA and relax it
Monika jangid
July 29, 2025Topoisomerase II bind with supercoiled dna after binding dna strand come in relax form
Juber Khan
July 30, 2025Topoisomerase break only one strand of dna and topoisomerase 2 break both strands of dna so topoisomerase 2 essential for cutting dna strand to allow another segment to pass through thereby relaxing the super coil dna
Priya Dhakad
July 30, 2025Topoisomerase 2 are bind with supercoiled DNA and DNA strand comes in relax form
Sneha Kumawat
July 30, 2025Attached to supercoil DNA and relax it.. oppo ISO mere second dono strand ko break krta h and atp ka use kr dna ko untangle krta h
Sneha Kumawat
July 30, 2025Attached to supercoil DNA and relax it.. topoisomerase second dono strand ko break krta h and atp ka use kr dna ko untangle krta h top
Aafreen
July 30, 20254th is correct, Its primary function is to relieve supercoiling in DNA.
Niti tanwar
July 30, 2025Option 4 is correct bcz topoisomarase attached to supercoiled dna .
Deepika Sheoran
July 30, 2025The right answer is topoisomerase second
Is an enzyme that helps relieve the strain on dna by attaching to the supercoiled dna relaxing it back to the original condition.
Aman Choudhary
July 30, 2025Option 4 Attach to super coiled DNA and relax it ek previous question ke explanation me padh tha ye wale question ka concept easy hogaya 😊
Anisha jakhar
July 31, 2025Option 4. Topoisomerase 2 relaxes the supercoiling of DNA.
Khushi Mehra
July 31, 2025Topoisomerase 2nd binds to the super coiled dna and break the phosohodiester bond and unwind the dna strands to relax the supercoiling pd DNA
Shivani
July 31, 2025Attach to super coiled DNA and relax it.
Avni
July 31, 2025topoisomerase II relax supercoiled DNA
Dipti Sharma
July 31, 2025Topoisomerase II relaxes supercoiling and resolves dna tangles.
Mahima Sharma
August 2, 20254th
Vijay Marmat
August 2, 20254 done ✔️
Soniya Shekhawat
August 3, 2025Topoisomease 2 is primarily function to relax supercoiling of DNA.
Anita Choudhary
August 28, 2025Correct answer is 4 because topoisomerase ll binds super coild dna and relax it and double stranded DNA break
Alec
August 30, 2025Topoisomerase 2 because because it attaches the supercoiled Dna and helps it to relax.
Deepika Sheoran
November 6, 2025Topoisomerase second is an enzyme that helps relieve the strain on DNA by attaching to the supercoiled DNA relaxing it back to the original condition.