Final answer:
Helicase is the enzyme that unwinds DNA strands at the origin of replication, initiating the process of DNA replication by creating a replication fork.
Step-by-step explanation:
The enzyme responsible for unwinding the DNA at the start of replication is helicase. Helicase separates the DNA strands at the origin of replication. The process begins as helicase breaks the hydrogen bonds holding the two strands of the DNA double helix together, effectively creating a replication fork. Subsequently, DNA polymerase can attach and synthesize new strands using the original strands as templates.