Which enzyme is responsible for unwinding the double helix at the replication fork on the leading strand?

Which enzyme is responsible for unwinding the double helix at the replication fork on the leading strand?

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

Answer: (A)

Unwinding the double helix at the replication fork is accomplished by helicase. Helicase binds at the fork and uses energy from ATP hydrolysis to break the hydrogen bonds between base pairs, separating the two DNA strands and creating single-stranded templates. This opening allows the leading strand to be copied continuously by DNA polymerase in the 5' to 3' direction toward the fork, with single-strand binding proteins stabilizing the exposed strands to prevent re-annealing. Primase makes the RNA primer needed to start synthesis, but it does not unwind the helix. DNA polymerase builds the new DNA, while ligase seals nicks after synthesis. So the enzyme responsible for unwinding is helicase.

Unwinding the double helix at the replication fork is accomplished by helicase. Helicase binds at the fork and uses energy from ATP hydrolysis to break the hydrogen bonds between base pairs, separating the two DNA strands and creating single-stranded templates. This opening allows the leading strand to be copied continuously by DNA polymerase in the 5' to 3' direction toward the fork, with single-strand binding proteins stabilizing the exposed strands to prevent re-annealing. Primase makes the RNA primer needed to start synthesis, but it does not unwind the helix. DNA polymerase builds the new DNA, while ligase seals nicks after synthesis. So the enzyme responsible for unwinding is helicase.