Phases of transcription by Escherichia coli RNA polymerase: how is the process classically divided? Choose the correct description.
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AFour phases known as initiation, propagation, elongation, and termination
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BThree phases known as initiation, elongation, and termination
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CTwo phases known as initiation and termination
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DNone of the above
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EFive phases including promoter melting and proofreading as separate stages
Answer
Correct Answer: Three phases known as initiation, elongation, and termination
Explanation
Introduction / Context:Transcription is commonly described in phases to simplify a complex, dynamic pathway. In bacteria, the canonical phases are initiation, elongation, and termination.
Given Data / Assumptions:
- Initiation includes promoter binding, isomerization to open complex, and initial transcript synthesis.
- Elongation involves processive RNA synthesis and RNA polymerase pausing mechanisms.
- Termination ends RNA synthesis via intrinsic or rho-dependent pathways.
Concept / Approach:The standard tripartite division effectively captures the major mechanistic transitions without inventing a separate 'propagation' phase. Sub-steps exist, but the top-level framework remains three phases.
Step-by-Step Solution:List recognized phases: initiation → elongation → termination.Exclude nonstandard labels such as 'propagation.'Select the option describing three phases.
Verification / Alternative check:Biochemistry texts, lecture notes, and primary literature adopt this three-phase terminology for bacterial transcription.
Why Other Options Are Wrong:Adding 'propagation' is nonstandard. Two-phase and 'none of the above' options do not accurately describe established pedagogy.
Common Pitfalls:Confusing sub-steps within initiation (open complex formation) as separate phases.
Final Answer:Three phases known as initiation, elongation, and termination.