Which enzyme is primarily responsible for unwinding the DNA at the fork on the leading strand?

Which enzyme is primarily responsible for unwinding the DNA at the fork on the leading strand?

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

Answer: (C)

Unwinding the double helix at the replication fork is accomplished by helicase. This enzyme uses energy to break the hydrogen bonds between base pairs, separating the two strands so the replication machinery can access the templates. On the leading strand, DNA polymerase then synthesizes DNA continuously as the fork progresses. Primase lays down RNA primers to provide starting points for DNA polymerase but does not unwind DNA. Ligase seals nicks after synthesis, not the unwinding step. Therefore, helicase is the enzyme responsible for unwinding at the fork.

Unwinding the double helix at the replication fork is accomplished by helicase. This enzyme uses energy to break the hydrogen bonds between base pairs, separating the two strands so the replication machinery can access the templates. On the leading strand, DNA polymerase then synthesizes DNA continuously as the fork progresses. Primase lays down RNA primers to provide starting points for DNA polymerase but does not unwind DNA. Ligase seals nicks after synthesis, not the unwinding step. Therefore, helicase is the enzyme responsible for unwinding at the fork.