Final answer:
Topoisomerase relieves torsional strain in DNA replication by breaking and resealing the DNA's phosphate backbone, which prevents supercoiling ahead of the replication fork.
Step-by-step explanation:
In replication, topoisomerase reduces the torsional strain (torque) that builds up ahead of the replication fork as a result of unwinding the DNA helix. Topoisomerase achieves this by making a double-strand break in one segment of the DNA helix, passing another segment through the break, and then resealing the broken end of the DNA. This enzyme manages to relieve the pressure that results from supercoiling by breaking and reforming DNA's phosphate backbone ahead of the replication fork, thus ensuring smooth progression of the replication process without the DNA becoming damaged due to an increase in torsional stress.