Question

Briefly describe the following:

Transcription 

Answer 1

Transcription is the process of synthesising RNA from a DNA template. A segment of DNA gets copied into mRNA during the process. The process of transcription starts at the promoter region of the template DNA and terminates at the terminator region. The segment of DNA between these two regions is known as a transcription unit. The transcription requires RNA polymerase enzyme, a DNA template, four types of ribonucleotides, and certain cofactors such as Mg²⁺.

The three important events that occur during the process of transcription are as follows.

1. Initiation
2. Elongation
3. Termination

The DNA-dependent RNA polymerase and certain initiation factors (σ) bind at the double-stranded DNA at the promoter region of the template strand and initiate the process of transcription. RNA polymerase moves along the DNA and leads to the unwinding of the DNA duplex into two separate strands. Then, one of the strands, called the sense strand, acts as a template for mRNA synthesis. The enzyme RNA polymerase uses nucleoside triphosphates (dNTPs) as raw materials and polymerises them to form mRNA according to the complementary bases present on the template DNA. This process of opening of helix and elongation of polynucleotide chain continues until the enzyme reaches the terminator region. As RNA polymerase reaches the terminator region, the newly synthesised mRNA transcript along with the enzyme is released. Another factor called terminator factor (ρ) is required for the termination of the transcription.