Which enzyme unwinds the DNA double helix ahead of the replication fork?

Which enzyme unwinds the DNA double helix ahead of the replication fork?

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

Answer: (D)

During DNA replication, the double helix must be opened to expose the template strands. The enzyme that does this unwinding is helicase, which sits at the replication fork and uses energy from ATP to separate the two strands, creating the fork and generating single-stranded templates for DNA polymerases to copy. As the helix opens, torsional strain builds up ahead of the fork. Topoisomerase relieves this strain by making temporary cuts and resealing the DNA, preventing the strands from becoming over-wound. Primase then lays down short RNA primers on the single-stranded templates to provide starting points for DNA polymerases to begin synthesis. Finally, DNA ligase seals nicks between Okazaki fragments on the lagging strand to produce a continuous DNA strand.

During DNA replication, the double helix must be opened to expose the template strands. The enzyme that does this unwinding is helicase, which sits at the replication fork and uses energy from ATP to separate the two strands, creating the fork and generating single-stranded templates for DNA polymerases to copy.

As the helix opens, torsional strain builds up ahead of the fork. Topoisomerase relieves this strain by making temporary cuts and resealing the DNA, preventing the strands from becoming over-wound.

Primase then lays down short RNA primers on the single-stranded templates to provide starting points for DNA polymerases to begin synthesis. Finally, DNA ligase seals nicks between Okazaki fragments on the lagging strand to produce a continuous DNA strand.