Which enzyme plays a key role in unwinding the DNA helix during replication?

Helicase is the enzyme responsible for unwinding the DNA helix during replication. This process is crucial for DNA replication because it separates the two strands of the double helix, allowing each strand to serve as a template for synthesizing the new complementary DNA strands.

The unwinding action of helicase results in the formation of a replication fork, where the two strands of DNA are temporarily separated. This action is essential for subsequent processes, such as the addition of nucleotides by DNA polymerase, which builds new strands based on the templates provided by the unwound DNA.

In contrast, other enzymes mentioned have different roles: DNA ligase is involved in joining Okazaki fragments on the lagging strand, DNA polymerase synthesizes new DNA strands by adding nucleotides to the existing templates, and restriction enzymes function to cut DNA at specific sequences. Thus, helicase's role in unwinding the DNA is critical for the entire replication process to proceed smoothly.