Biology, asked by nazakath6203, 11 months ago

Step of transcription in eukaryotic cell

Answers

Answered by VIGNESHSHENOY
0

Initiation is the first step of eukaryotic transcription and requires RNAP and several transcription factors to proceed.

LEARNING OBJECTIVES

Describe how transcription is initiated and proceeds along the DNA strand

KEY TAKEAWAYS

Key Points

Eukaryotic transcription is carried out in the nucleus of the cell and proceeds in three sequential stages: initiation, elongation, and termination.

Eukaryotes require transcription factors to first bind to the promoter region and then help recruit the appropriate polymerase.

RNA Polymerase II is the polymerase responsible for transcribing mRNA.

Key Terms

repressor: any protein that binds to DNA and thus regulates the expression of genes by decreasing the rate of transcription

activator: any chemical or agent which regulates one or more genes by increasing the rate of transcription

polymerase: any of various enzymes that catalyze the formation of polymers of DNA or RNA using an existing strand of DNA or RNA as a template

Steps in Eukaryotic Transcription

Eukaryotic transcription is carried out in the nucleus of the cell by one of three RNA polymerases, depending on the RNA being transcribed, and proceeds in three sequential stages:

Initiation

Elongation

Termination.

Initiation of Transcription in Eukaryotes

Unlike the prokaryotic RNA polymerase that can bind to a DNA template on its own, eukaryotes require several other proteins, called transcription factors, to first bind to the promoter region and then help recruit the appropriate polymerase. The completed assembly of transcription factors and RNA polymerase bind to the promoter, forming a transcription pre-initiation complex (PIC).

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. Only about 10-15% of mammalian genes contain TATA boxes, while the rest contain other core promoter elements, but the mechanisms by which transcription is initiated at promoters with TATA boxes is well characterized.

The TATA box, as a core promoter element, is the binding site for a transcription factor known as TATA-binding protein (TBP), which is itself a subunit of another transcription factor: Transcription Factor II D (TFIID). After TFIID binds to the TATA box via the TBP, five more transcription factors and RNA polymerase combine around the TATA box in a series of stages to form a pre-initiation complex. One transcription factor, Transcription Factor II H (TFIIH), is involved in separating opposing strands of double-stranded DNA to provide the RNA Polymerase access to a single-stranded DNA template. However, only a low, or basal, rate of transcription is driven by the pre-initiation complex alone. Other proteins known as activators and repressors, along with any associated coactivators or corepressors, are responsible for modulating transcription rate. Activator proteins increase the transcription rate, and repressor proteins decrease the transcription rate.

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Answered by Anonymous
0

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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.

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