Q.8 During transcription

• (A) DNA Gyrase introduces negative supercoils and DNA Topoisomerase I removes negative supercoils
• (B) DNA Topoisomerase I introduces negative supercoils and DNA Gyrase removes negative supercoils
• (C) Both DNA Gyrase and DNA Topoisomerase I introduce negative supercoils
• (D) Both DNA Gyrase and DNA Topoisomerase I remove negative supercoils

  Transcription by RNA polymerase generates torsional stress: positive supercoils ahead, negative supercoils behind (twin-domain model). Topoisomerases regulate this in bacteria. This article solves the MCQ, identifying (A) as correct for exam success in biotechnology.

  Supercoiling Dynamics in Transcription

  RNA polymerase rotation unwinds DNA ahead (+ supercoils) and overwinds behind (- supercoils). DNA gyrase (type II topoisomerase) uses ATP to introduce negative supercoils, countering positive ones ahead. DNA topoisomerase I relaxes negative supercoils behind, maintaining template topology.​

  Correct Answer: (A) DNA Gyrase introduces negative supercoils and DNA Topoisomerase I removes negative supercoils
  Gyrase resolves positive supercoils by converting them to negative ones; Topo I specifically relaxes excess negative supercoils. This balance supports processive transcription in E. coli and relatives.

  Explanation of All Options

  Evaluate each based on enzymatic mechanisms:

  • (A) DNA Gyrase introduces negative supercoils and DNA Topoisomerase I removes negative supercoils
    Correct. Gyrase acts ahead of RNAP; Topo I behind, as validated by ChIP-seq showing co-recruitment to transcription units.

  • (B) DNA Topoisomerase I introduces negative supercoils and DNA Gyrase removes negative supercoils
    Incorrect. Topo I relaxes (removes) negative supercoils via single-strand nicks; gyrase introduces them.

  • (C) Both DNA Gyrase and DNA Topoisomerase I introduce negative supercoils
    Incorrect. Topo I relaxes, doesn’t introduce; only gyrase does via ATP-dependent double-strand passage.

  • (D) Both DNA Gyrase and DNA Topoisomerase I remove negative supercoils
    Incorrect. Gyrase introduces negative supercoils; both don’t remove them—Topo I relaxes negatives, gyrase targets positives indirectly.

  Option	Gyrase Action	Topo I Action	Accurate?
  (A)	Introduces negatives	Removes negatives	Yes ​
  (B)	Removes negatives	Introduces negatives	No
  (C)	Introduces negatives	Introduces negatives	No
  (D)	Removes negatives	Removes negatives	No

  Biotech Relevance

  Gyrase inhibitors (quinolones) block transcription; Topo I poisons aid research. For bioinformatics, model supercoiling in sequence analysis—align with molecular biology workflows.