Question

Write about three stages of transcription: initation, elongation and termination?

Answer 1

TRanscription is the process of forming RNA from DNA , it is the first step in gene expression . The whole process is gone through three stages i.e initiation, elongation and termination. RNA polymerase is the key enzyme of this process. RNA polymerase, utilizes a single-stranded DNA template strand to synthesize a complementary strand of RNA. Specifically, in  5' to 3' direction, adding new nucleotide one by one to the 3' end of the newly synthesized strand.

In the first stage ;Initiation enzyme RNA polymerase binds to a specific sequence of the template DNA strand which is called promoter sequence. After that, the RNA polymerase separates the DNA strands, providing the single-stranded DNA template needed for the further procedure of transcription.

Recognition sites Transcribed region 5' 3' H 3 -5' DNA Promoter RNA polymerase 5' 3' 3' -5' DNA -Single-stranded template

In the second stage ; Elongation, the template strand of DNA  acts as a template for RNA polymerase enzyme . As it "reads" this template strand one base at a time, it  builds an RNA molecule out of complementary nucleotides, making a chain that grows from 5' to 3' direction . The RNA transcript carries the same information as the non-template (coding) strand of DNA from which the RNA is transcribing  but the RNA contains the base uracil (U) instead of thymine (T) in DNA.

Transcription Coding strand RNA Polymerase Active DNA 5 3 3 Nascent RNA Direction of polymerization Template strand Transcription bubble

In the last stage ;termination is describing the ending of the transcription process.This happen when the RNA polymerase transcribes a sequence of the template DNA strand that called as terminator. There are mainly two types of termination one is Rho protein dependent where the a protein called Rho factor binds to a specific sequence and starts "climbing" up the transcript towards RNA polymerase.When it goes up to  transcription bubble,it pulls the RNA transcript and the template DNA strand apart, releasing the RNA molecule and finish the transcription.

In case of rho independent termination the transcribed nacent RNa forms hairpin like structure in itself and triggers the termination of the process.

Terminator DNA that encodes Rho binding site RNA polymerase Transcription stop point -3° 3' DNA 5' 3' Rho factor lo Rho binding site RNA