Final answer:
Helicase and topoisomerase play key roles in breaking and separating the DNA strands for replication.
Step-by-step explanation:
The DNA strand must be broken for it to separate. Helicase is responsible for separating the DNA strands at the origin of replication. It unwinds the DNA helix by breaking the hydrogen bonds between the base pairs. Topoisomerase breaks and reforms the phosphate backbone of DNA ahead of the replication fork, relieving the pressure that occurs due to the winding and unwinding of the DNA strands.