Which enzyme is a subtype of DNA topoisomerase found in bacteria and plants?

Which enzyme is a subtype of DNA topoisomerase found in bacteria and plants?

• A. DNA gyrase
• B. Topoisomerase I
• C. DNA ligase
• D. RNA polymerase

Answer: (A)

DNA topoisomerases manage DNA twist by cutting and rejoining strands. Type II topoisomerases cut both strands and use ATP to pass another duplex through, changing the DNA's overall supercoiling. DNA gyrase fits this role and is unique in bacteria (and in plant chloroplasts) for actively introducing negative supercoils into DNA, which helps genome compaction and makes replication and transcription more efficient. This characteristic—a bacterial/plant type II topoisomerase that creates negative supercoils—is why it’s the correct choice. Topoisomerase I, by contrast, is a type I enzyme that relieves supercoils by making single-strand breaks and does not introduce negative supercoils. DNA ligase seals nicks in the DNA backbone but isn’t a topoisomerase. RNA polymerase synthesizes RNA and doesn’t alter DNA supercoiling as its primary function.

DNA topoisomerases manage DNA twist by cutting and rejoining strands. Type II topoisomerases cut both strands and use ATP to pass another duplex through, changing the DNA's overall supercoiling. DNA gyrase fits this role and is unique in bacteria (and in plant chloroplasts) for actively introducing negative supercoils into DNA, which helps genome compaction and makes replication and transcription more efficient. This characteristic—a bacterial/plant type II topoisomerase that creates negative supercoils—is why it’s the correct choice.

Topoisomerase I, by contrast, is a type I enzyme that relieves supercoils by making single-strand breaks and does not introduce negative supercoils. DNA ligase seals nicks in the DNA backbone but isn’t a topoisomerase. RNA polymerase synthesizes RNA and doesn’t alter DNA supercoiling as its primary function.