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BIO NMDCAT Structure of DNA
nmdcat.online July 3, 2026

86. A molecular analysis of a mutant bacterial strain reveals a defect in DNA topoisomerase I. During gene transcription, this enzyme deficiency will result in the

A. Failure of the spliceosome to remove structural introns
B. Accumulation of excessive positive supercoiling ahead of the transcription bubble, stalling transcription
✓
C. Spontaneous conversion of the template strand into an RNA-DNA virus
D. Immediate loss of the poly-A tail from the structural transcripts

📝 Explanation

Unwinding the helix creates torsional strain and positive supercoils ahead of the moving polymerase; without topoisomerase to relieve this stress, transcription stalls.

📖 Additional Information

  • Failure of the spliceosome to remove structural introns
  • Accumulation of excessive positive supercoiling ahead of the transcription bubble, stalling transcription
  • Spontaneous conversion of the template strand into an RNA-DNA virus
  • Immediate loss of the poly-A tail from the structural transcripts

Unwinding the helix creates torsional strain and positive supercoils ahead of the moving polymerase; without topoisomerase to relieve this stress, transcription stalls.

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