A Level Biology Practice Exam

Which enzyme is responsible for the unwinding of DNA during replication?

1. DNA ligase

2. DNA polymerase

3. DNA helicase

4. RNA polymerase

The correct answer is: DNA helicase

The correct choice is indeed the enzyme DNA helicase. DNA helicase plays a crucial role in DNA replication by unwinding the double-stranded DNA helix, separating the two strands and allowing each strand to be copied individually. This is essential as it creates a replication fork, where the DNA can be accessed and replicated by other enzymes. Other enzymes listed do not perform this function; DNA ligase, for instance, is involved in joining Okazaki fragments together on the lagging strand during replication. DNA polymerase is responsible for synthesizing new DNA strands by adding nucleotides complementary to the template strand. RNA polymerase, although important for transcription (the process of synthesizing RNA from a DNA template), is not involved in DNA replication itself. Therefore, DNA helicase's specific role in unwinding the DNA makes it the correct answer in this context.