Which enzyme unwinds the DNA double helix and separates the strands in preparation for replication?

Which enzyme unwinds the DNA double helix and separates the strands in preparation for replication?

• A. Helicase
• B. Ligase
• C. Topoisomerase
• D. Primase

Answer: (A)

Unwinding the DNA double helix to expose the template strands is the job of helicase. It uses energy from ATP to break the hydrogen bonds between base pairs, pulling the two strands apart and forming a replication fork so DNA polymerases can access single-stranded templates for synthesis. Without this opening step, replication cannot begin. Other enzymes have different roles: ligase joins fragments on the lagging strand, topoisomerase relieves twisting tension ahead of the fork, and primase lays down RNA primers to start DNA synthesis. So the enzyme that unwinds and separates the strands is helicase.

Unwinding the DNA double helix to expose the template strands is the job of helicase. It uses energy from ATP to break the hydrogen bonds between base pairs, pulling the two strands apart and forming a replication fork so DNA polymerases can access single-stranded templates for synthesis. Without this opening step, replication cannot begin. Other enzymes have different roles: ligase joins fragments on the lagging strand, topoisomerase relieves twisting tension ahead of the fork, and primase lays down RNA primers to start DNA synthesis. So the enzyme that unwinds and separates the strands is helicase.