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Name the enzyme that facilitates opening of DNA helix during transcription.
In DNA replication, DNA Helicase opens the double helix. But in TRANSCRIPTION, RNA polymerase is a versatile holoenzyme that binds the promoter, unwinds/opens the DNA helix to create the transcription bubble, and catalyzes RNA chain elongation! Mark RNA polymerase (Option 4) in 5 seconds.
In replication, a dedicated DNA helicase unwinds the duplex DNA ahead of the replication fork, followed by single-stranded binding proteins (SSBs).
In transcription, RNA polymerase binds to the promoter sequence (with the assistance of sigma factor in prokaryotes) and possesses intrinsic helicase-like activity that melts roughly 14 base pairs of DNA to form an open promoter complex (transcription bubble).
NCERT states: "RNA polymerase facilitates opening of the helix and continues elongation." It is capable of catalyzing the polymerization as well as unwinding the DNA template without needing a separate helicase.
DNA ligase joins Okazaki fragments; DNA helicase functions in replication; DNA polymerase synthesizes DNA. Only RNA polymerase performs this function during transcription.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Incorrect; DNA ligase catalyzes phosphodiester bond formation between DNA fragments (molecular glue), having no unwinding function.
Incorrect; DNA helicase unwinds DNA during replication, not during transcription.
Incorrect; DNA polymerase synthesizes DNA during replication and cannot transcribe RNA.
Factually exact; RNA polymerase facilitates opening of the DNA helix during transcription and catalyzes RNA elongation.
DNA replication uses DNA Helicase to unwind DNA. Transcription uses RNA Polymerase itself to open the helix!
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