Mechanism of Transcription

Introduction

Transcription is a process through which a gene's DNA sequence is copied ( transcribed ) to form an RNA molecule. Transcription is a series of steps involving the activation of ribonucleotides, the formation of DNA template, base pairing, chain formation, separation of  RNA  and duplex formation. This post is to briefly explain the process of transcription. 

Table of Contents

1. Introduction

2. Steps of Transcription

3. Activation of Ribo-nucleotides

4. Formation Of DNA Template

5. Base Pairing

6. Chain Formation

7. Separation of RNA

8. Duplex Formation

Steps of Transcription

Activation of Ribo-nucleotides

In this process, zyme phosphorylase along with the energy and phosphorylated Ribonucleotides get activated. The activated Ribonucleotides are adenosine triphosphate (ATP), guanosine triphosphate (GTP), uridine triphosphate (UTP) and cytidine triphosphate (CTP). 

 

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.

 

Base Pairing

 The Ribonucleoside triphosphates come closer to lie just opposite the nitrogenous bases of the DNA template (Antisense strand). This results in the formation of complementary pairs, I,e  they form complementary pairs, 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.

 

Chain Formation

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

 

Separation of RNA

 Separation is enhanced by the factor called 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.

 

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.

 

 



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