Which one of the following enzymes help the DNA to overcome the tension generated by the unwinding during replication?
Which one of the following enzymes help the DNA to overcome the tension generated by the unwinding during replication?
Select an option to attempt
Correct Answer: Option C
Explanation
Role of Topoisomerase at the replication fork:During DNA replication, helicase unwinds the double helix ahead of the replication fork. This unwinding creates POSITIVE SUPERCOILING (overwinding) ahead of the fork, creating torsional strain.Topoisomerase I: Cuts one strand, allows rotation, re-ligates — relieves supercoiling without ATP.Topoisomerase II (in bacteria: Gyrase): Cuts BOTH strands, passes another duplex through, re-ligates — relieves positive supercoiling and introduces negative supercoiling.Function at replication fork:• Topoisomerase (especially gyrase in bacteria) relieves the positive supercoiling (torsional stress) that accumulates AHEAD of the advancing replication fork.• Helicase unwinds DNA but does NOT relieve the resulting torsional strain — topoisomerase is needed for that.Answer: Topoisomerase relieves torsional strain (supercoiling) ahead of the replication fork.