Final answer:
A topoisomerase is the enzyme responsible for breaking and resealing the DNA strand ahead of the replication fork, thereby relieving supercoiling tension during DNA replication.
Step-by-step explanation:
An enzyme that breaks DNA, dispels the tension, and reseals the strand ahead of a DNA replication fork is called a topoisomerase. This enzyme plays a critical role in DNA replication by relieving the pressure that results from supercoiling. As the DNA helix unwinds to allow for replication, it creates tension ahead of the replication fork, which can lead to supercoiling and strain on the DNA molecule. To mitigate this, the topoisomerase makes controlled cuts in the DNA’s phosphate backbone, allowing the DNA to relax and then resealing the breaks. This action prevents the strands from becoming too tightly wound and potentially breaking, ensuring the smooth progress of DNA replication.