During DNA replication, which enzyme unwinds the double helix by breaking hydrogen bonds?

• A. DNA Polymerase.
• B. Helicase.
• C. Ligase.
• D. Primase.

Answer: (B)

Hydrogen bonds between base pairs hold the two DNA strands together, so unwinding during replication requires an enzyme that can break those bonds and separate the strands. This role is played by helicase, which uses energy from ATP to move along the DNA and pry apart the strands, forming the replication fork. Once the strands are open, other players take over: primase lays down RNA primers to start synthesis, DNA polymerase builds the new DNA, ligase seals nicks on the lagging strand, and single-strand binding proteins stabilize the exposed templates while topoisomerase relieves twisting tension. The other enzymes don’t unwind the helix—polymerase makes DNA, ligase joins fragments, and primase provides primers.