Q.18 The enzyme responsible for removal of DNA supercoils is
- Helicase
- Topoisomerase
- DNA ligase
- DNA polymerase
Topoisomerase is the enzyme responsible for removing DNA supercoils.
Option Analysis
Helicase unwinds the DNA double helix at the replication fork by breaking hydrogen bonds between strands, but it does not address supercoiling tension ahead of the fork. This creates positive supercoils that need separate relief.
Topoisomerase cuts one (type I) or both (type II) DNA strands, allows rotation to relieve torsional stress from supercoiling, then religates the strands without net unwinding. It prevents DNA tangling during replication and transcription.
DNA ligase joins Okazaki fragments on the lagging strand by forming phosphodiester bonds between 3′-OH and 5′-phosphate ends, but plays no role in supercoil management.
DNA polymerase synthesizes new DNA strands by adding nucleotides to the 3′ end using the template, without impacting supercoils.
The enzyme responsible for removal of DNA supercoils is topoisomerase, essential in molecular biology for managing DNA topology during replication and transcription. Supercoils arise as helicase unwinds DNA, creating torsional stress that topoisomerase relieves by strand breakage and rejoining.
Role in DNA Processes
Topoisomerase prevents overwinding ahead of the replication fork, ensuring smooth progression. Type I enzymes nick one strand for rotation; type II (like DNA gyrase) cut both strands, using ATP for decatenation.
Why Not Other Enzymes?
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Helicase separates strands but generates supercoils.
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DNA ligase seals nicks post-replication.
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DNA polymerase extends primers.
Enzyme Function Handles Supercoils? Helicase Unwinds DNA No Topoisomerase Relieves supercoils Yes DNA ligase Joins fragments No DNA polymerase Synthesizes DNA No This makes topoisomerase the clear answer for removal of DNA supercoils in exams like yours.
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