Mechanism of Transcription

Introduction

Transcription is a layman term used in a variety of contexts. You might have heard or transcription in a classroom where teachers dictate the keynotes. At this point of time you will pen down the words in a rough note and you will later transcribe it to the original notes. So, transcription is generally called as copying something in a meaningful way. In genetics, transcription is a process through which a gene's DNA sequence is copied ( transcribed ) to form an RNA molecule. it is the first of various steps of DNA based gene expression in which a particular segment of DNA is copied into RNA with the help of the enzyme RNA polymerase. Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. Transcription involves the activation of ribonucleotides, the formation of DNA template, base pairing, chain formation, separation of  RNA  and duplex formation. The whole idea of these steps is to synthesize proteins and this post will take you through the steps involved in the transcription. 

 

Steps of Transcription

1. Activation of Ribo-nucleotides

It is the first phase of transcription. During the activation of ribonucleotides, zyme phosphorylase along with the energy and phosphorylated Ribonucleotides are activated. The activated Ribonucleotides includes adenosine triphosphate (ATP), guanosine triphosphate (GTP), uridine triphosphate (UTP) and cytidine triphosphate (CTP). 

 

2. Formation Of DNA Template

 In order to form a template, 4 major regions are required, namely, initiation site, a promoter region, coding region, and a terminator region. As the name indicates, the initiation site help in starting the transcription process.  A promoter region has an RNA polymerase recognition site and binding site. In a coding region, the chain opening occurs. Chain opening needs unwindases, gyrases, and single-stranded binding proteins.  In a terminator region, the two strands of DNA uncoil progressively from the site of polymerase binding. One of the two strands of DNA (3’—» 5′) functions as a template for transcription of RNA. It is called a master template or antisense strand.

 

 

 

3. Base Pairing

The Ribonucleoside triphosphates come closer to lie just opposite to the nitrogenous bases of the DNA template (Antisense strand). This results in the formation of complementary pairs, I,e U goes opposite A, A goes opposite T, С goes opposite G, and G goes opposite C. A pyrophosphate is released from each ribonucleoside triphosphate to form Ribonucleotides. The pyrophosphate is hydrolyzed with the help of enzyme pyrophosphatase. It releases energy.

 

4. Chain Formation

 With the help of RNA polymerase, the adjacent ribonucleotides are held tightly against the DNA template to form an RNA chain.

 

5. Separation of RNA

Separation is enabled by  ATPase activity. This helps in the release of the completed RNA chain from the previous phase of chain formation. The released RNA is called primary transcript which will further get processed to form a functional RNA.

 

6.Duplex Formation

Once the primary transcript is released, the 2 strands of DNA form linkages amongst complementary base pairs. At this stage, Gyrases, unwindases and SSB proteins are released, consequently, there is double-helical DNA formation.

 

7. Post-Transcription Processing

The primary transcript is often larger than the functional RNAs. It is called hetero­geneous or hnRNA especially in case of mRNA. Post-transcription processing helps to convert the primary transcript into functional RNAs.

 

Read more

1.     

Replication of DNA

2.

Differences between DNA and RNA

3.

Introduction to genetics and heredity           

4.

Genetics and gene therapy

5.

HGP

 

Questions

  1. What are the phases of transcription, enlist them?

  2. Name the 4 regions responsible for the  Formation Of DNA Template.

  3. What is duplex formation

  4. Name the enzymes help in the transcription process.

  5. Explain the process of elongation of chain.

 

 



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