Which enzyme relieves torsional strain during replication?

Which enzyme relieves torsional strain during replication?

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

Answer: (B)

Torsional strain ahead of the replication fork is relieved by a topoisomerase. As helicase unwinds the DNA, the remaining helix becomes increasingly twisted, creating positive supercoiling that would hinder progression. Topoisomerase relieves this by briefly cutting one strand (or both strands in the larger class), letting the DNA rotate and unwind the excess twist, then resealing the breaks. This prevents stalling and keeps replication moving. The other enzymes have different roles: primase lays down RNA primers, DNA polymerase builds the new strand, and DNA ligase seals nicks after fragments are joined.

Torsional strain ahead of the replication fork is relieved by a topoisomerase. As helicase unwinds the DNA, the remaining helix becomes increasingly twisted, creating positive supercoiling that would hinder progression. Topoisomerase relieves this by briefly cutting one strand (or both strands in the larger class), letting the DNA rotate and unwind the excess twist, then resealing the breaks. This prevents stalling and keeps replication moving. The other enzymes have different roles: primase lays down RNA primers, DNA polymerase builds the new strand, and DNA ligase seals nicks after fragments are joined.