Life Science Practice Exam

During DNA replication, the two strands must be separated so each can serve as a template. This separation is performed by helicase, an enzyme that uses energy from ATP hydrolysis to disrupt the hydrogen bonds between the base pairs, effectively unzipping the double helix and forming the replication fork. Once the strands are separated, DNA polymerases can access each template to synthesize new strands. Other enzymes assist in the process: topoisomerase relieves the twisting ahead of the fork to prevent tangling, ligase seals the gaps after fragments are synthesized, but the step that actually unzips the DNA is carried out by helicase.