Which enzyme relieves torsional stress in DNA by cutting and rejoining strands?

Which enzyme relieves torsional stress in DNA by cutting and rejoining strands? The answer is topoisomerase. These enzymes temporarily break DNA strands, allow the molecule to rotate or pass through itself, and then reseal the breaks.

DNA becomes twisted and strained when it is unwound for replication or transcription. The strain can build up ahead of a replication fork, much like kinks forming in a twisted rope. Topoisomerases prevent this torsional stress from blocking essential cellular processes.

Type I topoisomerases generally cut one DNA strand at a time, while type II topoisomerases cut both strands and pass another DNA segment through the break. The enzyme then reseals the DNA, changing its linking and supercoiling state.

DNA ligase also joins broken DNA, but its usual role is sealing nicks, such as those between Okazaki fragments. Helicase separates the two DNA strands, and DNA polymerase builds a new strand. Those enzymes work alongside topoisomerases, but they do not perform the same stress-relieving cutting-and-rejoining function.