Transcription in Prokaryotes - Practice Questions & MCQ

• The process of transcription occurs in the following three stages:
  • Initiation
  • Elongation 
  • Termination 

Initiation:

• During initiation, the RNA polymerase holoenzyme binds to the promoter region of the transcription unit.
•  The RNA polymerase-sigma complex binds to the promoter and initiates transcription of a specific strand of DNA. 
• The DNA strand unwinds by the action of this complex. No primer is required for RNA synthesis.
• RNA polymerase holoenzyme uses nucleoside triphosphates as substrate and polymerises in a template depended fashion following the rule of complementarity. 

Elongation: 

• The transcription elongation phase begins with the release of the σ subunit from the polymerase. 
• The dissociation of σ allows the core enzyme to proceed along the DNA template, synthesizing mRNA in the 5' to 3' direction at a rate of approximately 40 nucleotides per second.
• As elongation proceeds, the DNA is continuously unwound ahead of the core enzyme and rewound behind it.

Termination:

• Depending on the gene being transcribed, there are two kinds of termination signals:
  • One is protein-based called Rho-dependent termination.
  • The other is RNA based called Rho-independent termination
• In bacteria, since the mRNA does not require any processing to become active, and also since transcription and translation take place in the same compartment (there is no separation of cytosol and nucleus in bacteria), many times the translation can begin much before the mRNA is fully transcribed. 
• Consequently, the transcription and translation can be coupled in bacteria.