Question

Structure of promoter in transcription in eukaryotes

Answer 1

The most-extensively studied core promoter element in eukaryotes is a short DNA sequence known as a TATA box, found 25-30 base pairs upstream from the start site of transcription. Transcription factors recognize the promoter, RNA polymerase II then binds and forms the transcription initiation complex.

Answer 2

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•Transcription is the process of synthesis of RNA from 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 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.

(i) Initiation

(ii) Elongation

(iii) 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 DNA duplex into two separate strands.

•Then, one of the strands, called sense strand, acts as template for mRNA synthesis.

•The enzyme, RNA polymerase, utilizes nucleoside triphosphates (dNTPs) as raw material and polymerizes 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 synthesized mRNA transcripted along with enzyme is released.

•Another factor called terminator factor (ρ) is required for the termination of the transcription.