Question

The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be ""overwound"" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication?

Answer 1

Answer: The tension is relieved by an enzyme named topoisomerase

Explanation:

As replication starts DNA polymerase needs to move forward of double strand DNA, this creates a lot of tension in the DNA molecule. The tension is relieved by the action of an enzyme named  topoisomerase. The stress relieve is needed for the progresion of the  replication mechanism.

There are to types of topoisomerases:

a) Topoisomerase I

b) Topoisomerase II

Topoisomerase I underwinds the DNA double helix by making a single cut  in one of the strands of the DNA molecule. Once the cut is made, the DNA unwinds and torsional stress is released. Finally the DNA strand , that was cut is ligated ( see attached image)

Topoisomerase II acts when torsional stress is made because two DNA strands cross each other (superhelical stress). Topoisomerase II cuts both strands of a DNA molecule. After this cut is made the DNA unwinds and torsiona stress is relieved ). Finally both  DNA strands are ligated ) see attached image)

Topoisomerases II enzymes require ATP hydrolysis to perform the cut of both of the DNA strands.