Which enzyme unwinds the DNA double helix during replication?

During DNA replication, the enzyme that unwinds the DNA double helix is helicase. This enzyme plays a crucial role in initiating the process of replication by breaking the hydrogen bonds between the complementary base pairs, effectively separating the two strands of the DNA molecule. This unwinding creates a replication fork where the DNA strands are accessible for the next steps of replication.

The activity of helicase is essential for allowing other enzymes, such as DNA polymerase, to synthesize new DNA strands based on the template provided by the unwound strands. Without helicase, the double-stranded structure of DNA would remain intact, and replication could not occur.

Other enzymes mentioned, such as primase, are involved in synthesizing RNA primers necessary for DNA polymerase to start replication, while ligase is responsible for joining Okazaki fragments on the lagging strand. Topoisomerase helps relieve the tension and supercoiling that occurs ahead of the replication fork but does not directly unwind the double helix itself.