Question

Choose the correct sequence of events as they occur during a bacterial transcription
A. RNA polymerase sigma (\(\sigma\)) subunits recognizes promoters
B. DNA double helix unwind
C. Sigma (\(\sigma\)) subunit dissociates from the holoenzyme
D. Formation of hairpin secondary structure
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. A, C, B, D
• C. B, A, D, C
• D. C, B, D, A

Hint:

Think of transcription like a train journey. \textbf{A}: The conductor (\(\sigma\)-factor) finds the station (promoter). \textbf{B}: The doors open (DNA unwinds). \textbf{C}: The train leaves the station and the conductor gets off (\(\sigma\)-factor dissociates). \textbf{D}: The train reaches its destination and the brakes are applied (hairpin forms for termination).

Answer 1

The Correct Option is A

Step 1: Concept Overview:
Bacterial transcription consists of initiation, elongation, and termination. This question requires arranging the events of these stages in chronological order.
Step 2: Detailed Breakdown:
Analyzing the event sequence:


Initiation (Step A): RNA polymerase holoenzyme, specifically the \(\sigma\) subunit, recognizes and binds to the promoter sequence on the DNA.

Initiation (Step B): RNA polymerase unwinds a short DNA segment at the promoter, creating an "open complex" and exposing the template strand.

Elongation (Step C): After synthesizing approximately 10 nucleotides, the \(\sigma\) subunit dissociates from the core enzyme, which continues RNA synthesis.

Termination (Step D): Termination occurs at a terminator sequence. Rho-independent termination involves a stable hairpin structure forming in the RNA, signaling RNA polymerase to detach from the DNA.

Step 3: Conclusion:
The chronological order is A \(\rightarrow\) B \(\rightarrow\) C \(\rightarrow\) D.