Q.174 Zoology ⭐ 360° Option Elimination Active
NEET 2025 Zoology Question 174 Solution
Topic: Molecular Basis of Inheritance · Official NTA Booklet Code 45
Question
Which factor is important for termination of transcription?
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Verified Against NTA Final Answer Key
Option (3) : ρ (rho)
📚 Molecular Basis of Inheritance Easy
📋 Given Parameters & Problem Setup
Process Bacterial transcription termination
Target Molecular Factor Protein factor responsible for terminating RNA synthesis
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⏱️ Save ~10 seconds The 30-Second Exam Hall Shortcut: ⚡ Bacterial Transcription Factors Fingerprint
Sigma (σ) factor initiates transcription! Rho (ρ) factor terminates transcription! Rho = RHO-cks the enzyme off the DNA (TERMINATION)!
1 Recall NCERT Section 6.5.2 (Transcription in Prokaryotes) verbatim:
2 - In bacteria, a single DNA-dependent RNA polymerase catalyzes transcription of all three types of RNA.
3 - "It associates transiently with initiation-factor (σ) and termination-factor (ρ) to initiate and terminate the transcription, respectively."
4 - Initiation factor = (sigma).
5 - Termination factor = (rho).
6 Direct answer: (rho)!
7 Select Option (3) (rho)!
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Why You Can 100% Trust This Shortcut: Genetic Code Characteristics (NCERT Biology · Molecular Basis of Inheritance: Triplet, degenerate, unambiguous, non-overlapping).
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Catalytic Activity of Bacterial RNA Polymerase Core Enzyme
Bacterial RNA polymerase core enzyme (alpha_2 eta eta' omega) is catalytically competent for chain elongation but cannot recognize promoters or terminate faithfully on its own:
- • To ensure stage-specific regulation, the core enzyme associates reversibly with auxiliary protein factors.
- • Initiation: The core enzyme binds the sigma () factor to form the holoenzyme, enabling sequence-specific promoter recognition at the (Pribnow box) and consensus sequences.
Step 2
Mechanism of Transcription Termination by Rho (ρ) Factor
How RNA synthesis is brought to an end:
- • Elongation proceeds until the polymerase reaches a terminator sequence.
- • In rho-dependent termination, the termination factor rho () (an ATP-dependent hexameric RNA helicase) binds to a C-rich *rut* site on the nascent RNA transcript.
- • Rho migrates along the RNA transcript toward the stalled RNA polymerase.
- • Upon contacting the transcription elongation complex, Rho unwinds the RNA-DNA hybrid within the transcription bubble, releasing the newly synthesized nascent RNA chain and dissociating RNA polymerase from the template DNA.
Step 3
Conclusion
The factor important for the termination of transcription is (rho), corresponding to Option (3).
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 A
✗ Incorrect Verdict & Scientific Reason:
Incorrect. The subunit is a structural core subunit responsible for enzyme assembly and upstream promoter interaction, not a termination factor.
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Student Fallacy (Why candidates pick this trap): Confusing core enzyme subunits with transient regulatory factors.
2 B
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Sigma () is the INITIATION factor, the exact opposite of termination.
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Student Fallacy (Why candidates pick this trap): Confusing initiation factor with termination factor.
3 C
✓ 100% Correct Verdict & Scientific Reason:
100% correct. Direct verbatim NCERT fact: termination factor is (rho).
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Why this is airtight: None; textbook mastery.
4 D
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Gamma is not a transcription factor in prokaryotic RNA synthesis.
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Student Fallacy (Why candidates pick this trap): Arbitrary selection of a Greek letter.
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NTA Trap Alert: Sigma vs Rho Factor Role Inversion
The two famous Greek factors in transcription: = START (Initiation); = RELEASE (Termination). Never swap them!
🛡️ How to avoid the -1 mark: Sigma = Start (Initiation); Rho = Release/Halt (Termination).
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Core NEET Syllabus Standard
NEET Biology Core Syllabus · Molecular Basis of Inheritance Standard Benchmark
Core Scientific Principle Tested:
"RNA polymerase transiently associates with initiation-factor (σ) and termination-factor (ρ) to initiate and terminate transcription."
Syllabus Focus: Transcription · Process of Transcription in Bacteria
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
Sigma = START; Rho = RELEASE (Termination)!
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