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Which is the "Only enzyme" that has "Capability" to catalyse Initiation, Elongation and Termination in the process of transcription in prokaryotes?
In bacteria, a single DNA-dependent RNA polymerase catalyses all three steps of transcription: it catalyses elongation alone, and binds transiently to initiation factor (sigma, σ) to start, and termination factor (rho, ρ) to end. Match Option (2) in 5 seconds!
In prokaryotes, there is only a single DNA-dependent RNA polymerase responsible for transcribing all three types of RNA (mRNA, tRNA, rRNA): 1. Initiation: The core RNA polymerase enzyme () associates transiently with the initiation factor, sigma () factor, allowing it to recognize and bind the promoter sequence specifically. 2. Elongation: The core enzyme itself unwinds the DNA helix and polymerizes ribonucleoside triphosphates processively in the direction. 3. Termination: Upon reaching the terminator region, the polymerase associates transiently with the termination factor, rho () factor, which dissociates the nascent RNA and halts transcription.
- DNA dependent DNA polymerase: Catalyses semi-conservative DNA replication, not transcription. - DNA Ligase: Catalyses phosphodiester bond formation between Okazaki fragments or recombinant DNA ends. - DNase: Hydrolyses and degrades DNA strands.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Incorrect. This enzyme catalyses DNA replication, not transcription of RNA from a DNA template.
Correct. In bacteria, DNA-dependent RNA polymerase is the sole enzyme that carries out elongation, while recruiting sigma and rho factors to execute initiation and termination.
Incorrect. Ligase joins DNA fragments during replication and repair.
Incorrect. DNase is a catabolic nuclease that breaks down DNA.
Some candidates think sigma and rho are separate independent enzymes that perform initiation and termination alone. NCERT explicitly clarifies that sigma and rho are non-catalytic protein factors that associate with RNA polymerase to confer initiation and termination capabilities.
"In bacteria, a single DNA-dependent RNA polymerase catalyses all three steps of transcription (initiation, elongation, and termination) with the help of sigma and rho factors."
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