Which enzyme is responsible for opening the DNA helix during replication?

The enzyme responsible for opening the DNA helix during replication is helicase. Helicase works by unwinding the double-stranded DNA at the replication fork, separating the two strands to allow the template strands to be accessible for copying. This unwinding is crucial because it prepares the DNA for the synthesis of new strands. The action of helicase is essential for the initiation of DNA replication, as it creates the replication fork structure needed for other enzymes to function properly in the replication process.

While ligase is involved in joining Okazaki fragments on the lagging strand, primase synthesizes short RNA primers needed to start DNA synthesis, and topoisomerase relieves the tension created ahead of the replication fork by making temporary cuts in the DNA strands, it is specifically helicase that primarily initiates the process of separating the DNA strands for replication.