Final answer:
As DNA strands are separated at the replication fork, the dsDNA in front of the fork becomes positively supercoiled. Topoisomerase enzymes break and reform the DNA's sugar backbone ahead of the fork to relieve the pressure caused by supercoiling.
Step-by-step explanation:
As the strands of DNA are separated at the replication fork, the dsDNA in front of the fork becomes increasingly positively supercoiled. This supercoiling is caused by the action of helicase, which unwinds the DNA strands, and the formation of the replication bubble. Topoisomerase enzymes break and reform the DNA's sugar backbone ahead of the replication fork to relieve the pressure caused by supercoiling. Single-strand binding proteins prevent the rewinding of the DNA.