Which enzyme stabilizes the DNA strand and prevents it from breaking?

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

Answer: (D)

Relief of torsional stress in the DNA during unwinding is the key idea. As the double helix opens, positive supercoils build up ahead of the fork. If this tension isn’t managed, the strands can become damaged or break. DNA gyrase does the essential job of relieving this stress by creating transient breaks in the DNA, passing another segment through, and then resealing. This relieves supercoiling and adds negative supercoils, helping stabilize the backbone and prevent breakage during replication and transcription. The other enzymes have different roles: helicase unwinds the strands, which increases the need to manage torsion but doesn’t prevent breakage by itself; primase synthesizes RNA primers for initiation; DNA polymerase synthesizes new DNA and checks for errors, but it isn’t the main factor in preventing backbone breakage due to torsional stress.