The flow of genetic Information from DNA to mRNA - Transcription

 

• The process of transfer of genetic information from DNA to RNA is known as transcription.

• In transcription only one strand of DNA is participated; if both strands aur involved in transcription then it will produce two kinds of RNA and they will produce two different kinds of protein it may create complications among the organism.

• If two RNA molecules are synthesised both double strands of RNA may  combine and form a double strand RNA. 

Transcription unit. 

• There are three basic regions in the transcription unit. These are promoter structural and Terminator.

• Promoter is located at five prime end with respect to polarity of coding strand and terminator is located at 3 prime and with respect to the polarity of the coding strand.

• The DNA strand with polarity 3 Prime to 5  Prime is known as template strand whereas the DNA strand  with  polarity 5 prime  to  3 Prime is known as the coding strand template strand is involved in transcription whereas coding strand is not involved in transcription. 

Transcription in prokaryotes

• In prokaryotes the process of transcription is Polycistronic.

• In prokaryotes the process of transcription includes three steps: initiation , elongation and termination. The RNA polymerase recognise the promoter region all templates time and bind with the promoters.

• As RNA polymerase binds to the promoter the transcription process starts. This is known as initiation.

• The RNA polymerase starts to open the DNA helix and catalyse the process of elongation. The new RNA is synthesised according to the nitrogenous base present on DNA template strand.

• As a result the length of RNA is increased by the process of elongation. As RNA polymerase reaches the Terminator region the RNA polymerase falls off and newly synthesised RNA  or nascent RNA  is released in cytoplasm. This is known as termination. 

• During transcription the initiation elongation and termination are associated with the sigma  factor (σ) omega factor (ω) and  rho factor(ρ) respectively. 

Transcription in eukaryotes

• The process of transcription is always similar in both prokaryotes and eukaryotes except some complications. 

• In prokaryotes the process of transcription is Polycistronic whereas in eukaryotes the process is known as Monocistronic. 

• In Prokaryotes single RNA polymerase enzyme synthesises all different Three types of RNA whereas in eukaryotes the three types of RNA polymerase synthesise three different types of RNA molecule.

• RNA polymerase first  synthesised  rRNA. RNA polymerase 2nd synthesised mRNA. and RNA polymerase third synthesised tRNA molecule. tRNA molecule also known as  Soluble RNA.

• In prokaryotes a process called  splicing does not take place whereas in eukaryotes splicing occurs. 

• During splicing the intron or non coding sequence are removed whereas Exon or coding sequence are added.

• During splicing, capping and tailing also occurs. This step of splicing is necessary for the formation of a hn RNA or heterogeneous nuclear RNA.

• The capping takes place at the three prime ends of hn RNA. During capping methyl Guanosine triphosphate is added  at three prime ends. where as tailing takes place at five prime and during this process adenylate residue  Residue is added.

• After the complete process of the splicing,  hn RNA is converted into mRNA which is released from nucleus to cytoplasm and attached to a small subunit of ribosome for the protein synthesis.