DNA gyrase, a type II topoisomerase in bacteria, primarily introduces negative supercoils into circular DNA. This action compacts the genome and facilitates strand separation for essential processes.

Correct Answer

Negative supercoiling is the key function of DNA gyrase in circular DNA.

Option Breakdown

Negative supercoiling

DNA gyrase uses ATP to create negative supercoils, counteracting positive supercoils ahead of replication forks in closed circular bacterial DNA. This underwinds the helix, promoting unwinding for replication and transcription.

✅ Correct: Essential for bacterial genome maintenance.

Positive supercoiling

Positive supercoiling overwinds DNA, increasing torsional stress; gyrase does the opposite by removing it via negative supercoiling. Other enzymes like topoisomerase I relax positive supercoils.

❌ Incorrect: Gyrase actively prevents this.

DNA packaging

Packaging in bacteria involves nucleoid-associated proteins like HU or H-NS, not gyrase. While supercoiling aids compaction indirectly, gyrase’s direct role is topological control.​

❌ Incorrect: Not gyrase’s primary enzymatic function.

DNA degradation

Gyrase transiently breaks and rejoins DNA strands without degradation; it preserves integrity during topology changes. Degradative enzymes like nucleases perform breakdown.​

❌ Incorrect: Gyrase protects, does not destroy DNA.