Which enzyme is responsible for unzipping/separating the double helix during the first step of DNA replication?

Which enzyme is responsible for unzipping/separating the double helix during the first step of DNA replication?

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

Answer: (C)

Unwinding the double helix at the replication fork is the first step in DNA replication. This job is carried out by helicase, a motor enzyme that uses energy from ATP hydrolysis to separate the two strands by breaking the hydrogen bonds between base pairs. With the strands separated, primase adds RNA primers to provide starting points for DNA synthesis, and DNA polymerase extends from those primers to build new DNA strands. Topoisomerase helps relieve torsional strain ahead of the fork so unwinding can continue smoothly. The unzipping is the specific function of helicase, making it the correct choice.

Unwinding the double helix at the replication fork is the first step in DNA replication. This job is carried out by helicase, a motor enzyme that uses energy from ATP hydrolysis to separate the two strands by breaking the hydrogen bonds between base pairs. With the strands separated, primase adds RNA primers to provide starting points for DNA synthesis, and DNA polymerase extends from those primers to build new DNA strands. Topoisomerase helps relieve torsional strain ahead of the fork so unwinding can continue smoothly. The unzipping is the specific function of helicase, making it the correct choice.