Which enzyme unwinds the DNA helix during replication?

Which enzyme unwinds the DNA helix during replication?

• A. Helicase
• B. Topoisomerase
• C. DNA polymerase
• D. Ligase

Answer: (A)

During DNA replication, the double helix must be opened so the polymerases can read the templates. The enzyme that does this opening is helicase. It binds at the replication fork and uses energy from ATP hydrolysis to separate the two strands, creating single-stranded templates for synthesis. This unwinding is the essential first step before new DNA can be synthesized. Other enzymes have important roles but don’t unwind the helix themselves: topoisomerase relieves torsional stress ahead of the fork, DNA polymerase builds the new strands, and ligase seals remaining nicks between fragments.

During DNA replication, the double helix must be opened so the polymerases can read the templates. The enzyme that does this opening is helicase. It binds at the replication fork and uses energy from ATP hydrolysis to separate the two strands, creating single-stranded templates for synthesis. This unwinding is the essential first step before new DNA can be synthesized. Other enzymes have important roles but don’t unwind the helix themselves: topoisomerase relieves torsional stress ahead of the fork, DNA polymerase builds the new strands, and ligase seals remaining nicks between fragments.