Process of Transcription: Know Stages, RNA Polymerase

What Is Transcription?

Transcription is the process of gene expression where DNA is copied into RNA. This is a very crucial stage in the gene expression process and plays a very central role in the production of mRNA, which ultimately dictates the synthesis of proteins. Transcription occurs as the synthesis of RNA from a DNA template. It plays a key role in the central dogma of molecular biology.

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This Story also Contains

1. What Is Transcription?
2. Where Does Transcription Take Place?
3. Central Dogma Of Molecular Biology
4. Mechanism Of Transcription
5. Post-Transcriptional Modifications In Eukaryotes
6. Mechanisms Of Transcription Regulation
7. Applications And Importance Of Transcription
8. The Video Recommended For The Process Of Transcription:

Where Does Transcription Take Place?

Transcription occurs in different cellular locations depending on whether the organism is a prokaryote or a eukaryote. In eukaryotic cells, it occurs inside the nucleus. In prokaryotic cells, it occurs in the cytoplasm.

Central Dogma Of Molecular Biology

• The central dogma explains the flow of genetic information within a biological system.

• DNA is transcribed into RNA, which is then translated into protein.

• This process underlies the flow of genetic information in cells.

Role Of Transcription In Central Dogma

• Transcription is one of the initial steps in the central dogma, where it joins DNA to the production of RNA.

• Transcription is the process by which the information contained in the DNA triple code is duplicated into a complementary RNA series.

• It facilitates the synthesis of proteins by the cell based on its genetic information.

Key Components Involved In Transcription

The primary components involved are:

DNA Template

• A strand of the DNA template is used by RNA polymerase to synthesise RNA.

• The antisense strand of DNA acts as a template for RNA synthesis.

• The sense strand is identical to the RNA transcript produced (except that thymine is replaced with uracil).

RNA Polymerase

• RNA polymerase is the enzyme that catalyses transcription.

• RNA polymerase binds to the DNA and synthesises RNA by adding nucleotides.

• Prokaryotes have only one type of RNA polymerase; eukaryotes have three types: I, II, and III.

Promoters And Transcription Factors

• Promoters are DNA sequences that mark the beginning of transcription, and transcription factors are proteins that bind to specific DNA sequences, facilitating the binding of RNA polymerase to DNA.

• Promoters lie upstream of the gene and thus play a crucial role in the initiation of transcription.

• Transcription factors modulate this binding of RNA polymerase to the promoter, hence regulating gene expression.

Mechanism Of Transcription

The following steps are seen in the mechanism of Transcription:

Step 1: Initiation

• The process of initiation is the beginning of RNA synthesis.

• RNA polymerase binds to the promoter region of the DNA.

• The transcription initiation complex is formed, and the process of DNA unwinding begins.

Step 2: Elongation

• In elongation, RNA polymerase travels along the DNA synthesising RNA.

• RNA polymerase adds nucleotides to the growing mRNA strand in a 5' to 3' direction.

• The DNA unwinds ahead of RNA polymerase and rewinds behind it.

Step 3: Termination

• Termination signals the end of transcription and the release of the RNA molecule.

• It is these specific terminator sequences in the DNA that cause the RNA polymerase to stop and release the mRNA transcript.

• In eukaryotes, termination is followed by other processing steps.

Diagram: Transcription Process in prokaryotes

Post-Transcriptional Modifications In Eukaryotes

The post-transcriptional modifications are:

5' Capping

• The 5' cap is attached to the 5' end of the mRNA molecule. It protects the mRNA from degradation.

• A modified guanine nucleotide is added to the 5' end of the mRNA.

• This cap is essential for mRNA stability and recognition by the ribosome.

Polyadenylation

• Essentially, this process adds a tail composed of adenine nucleotides to the 3' end of the mRNA.

• The poly-A tail protects mRNA from enzymatic degradation.

• It also facilitates the export of mRNA from the nucleus to the cytoplasm.

Splicing

• This is a step where the non-coding regions are removed from the pre-mRNA and the coding regions are joined together. The spliceosome complex cuts out introns and joins exons together.

• This process is essential for producing a functional mRNA transcript.

Alternative Splicing

• Alternative splicing allows a single gene to yield multiple variants of mRNA. This allows for increasing protein diversity.

• The joining of different sets of exons leads to the formation of different types of mRNAs.

• Different types of proteins originate from a single gene.

Mechanisms Of Transcription Regulation

The following are the mechanisms of the process of transcription:

Transcription Factors And Enhancers

• Transcription factors and enhancers are the most prominent players involved in gene expression.

• The modulation of the rate of transcription comes about by the binding of transcription factors to definite sequences of DNA.

• Enhancers raise the effectiveness of the transcriptional procedure through their interaction with the promoter region.

Epigenetic Regulation

• Epigenetic alterations may also affect transcription without any alteration in the DNA sequence.

• DNA methylation and histone alterations result in repression or activation of transcription.

• Such modifications are heritable and play a role in gene regulation.

Feedback Loops

• Cells adopt the system of feedback loops in regulating transcription as well as in the maintenance of homeostasis.

• Positive feedback is when the product produced through gene expression stimulates its transcription, increasing it.

• The negative feedback, on the other hand, is a turned-off expression of genes due to their products.

• Examples include the regulation of hormone production and metabolic pathways.

Applications And Importance Of Transcription

Understanding this process of transcription helps in:

Studies Of Gene Expression

• In studying gene function and expression, one needs to understand transcription.

• Transcription analysis studies how genes are regulated.

• Such knowledge can help comprehend the nature of diseases and developmental processes.

Medical Implications

• Hence, it is an area of medical research because diseases can emanate from transcription errors.

• Misregulation of transcription leads to cancer, genetic disorders, and other diseases.

• Targeting transcription factors has become a strategy for developing new therapies.

Applications In Biotechnology

• Transcription plays a huge role in genetic engineering or synthetic biology.

• Scientists manipulate transcription to produce recombinant proteins and genetically modified organisms.

• It is used in developing gene therapies and studying gene function.

The Video Recommended For The Process Of Transcription: