Transcription of DNA

Transcription of DNA is a cellular process where the genetic information encoded in DNA is converted into RNA. It initiates with RNA polymerase binding to the DNA at a specific promoter region. Then, the enzyme unwinds the DNA and synthesizes a complementary RNA strand by following the DNA template. This process continues until a termination signal is reached, leading to the release of the newly formed RNA molecule, which carries the genetic code for protein synthesis.

Transcription of DNA Definition

Transcription is the process of copying genetic information from DNA to RNA. It involves RNA polymerase creating a complementary RNA strand using a DNA template.

What is Transcription?

Transcription of DNA is a fundamnetal cellular process that converts the genetic information stored in DNA into RNA. Both DNA and RNA are nucleic acid. While DNA stores genetic information, RNA mostly helps in transfer and expression of information. DNA being chemically and structurally more stable is a better genetic material. The process of transcription is goeverned by the principle of complementarity. In transcription only a segment of DNA and only one of the strands is copied into RNA. This process occurs in three main stages: initiation, elongation, and termination.

The primary purpose of transcription is to generate RNA from the DNA sequence, with the resulting RNA transcript containing the instructions for protein synthesis.

RNA Polymerase

RNA polymerase is an important enzyme that take part in gene expression and the transcription of genetic information. It plays a central role in the process of transcription, where it copies DNA sequences into RNA molecules. RNA polymerase identifies specific promoter regions on the DNA, marking the initiation point for transcription. As it moves along the DNA template, RNA polymerase unwinds the double helix and synthesizes a complementary RNA strand. This synthesized RNA, primarily messenger RNA (mRNA), contains the instructions for protein synthesis. Multiple types of RNA polymerases exist, with RNA polymerase II predominantly transcribing protein-coding genes in eukaryotes. RNA polymerase regulates gene expression, enables the development and maintenance of living organisms and the functioning and regulation of various cellular processes.

Stages of Transcription

Transcription is the process of copying genetic information from DNA into RNA. It take place in following stages:

Initiation: This stage marks the beginning of transcription. RNA polymerase, along with other transcription factors, recognizes and binds to the promoter region on the DNA. The DNA double helix unwinds, exposing the template strand for transcription.

Elongation: Once the RNA polymerase is bound and the DNA is unwound, the enzyme moves along the DNA template strand. As it progresses, it synthesizes a complementary RNA strand by incorporating ribonucleotides according to the DNA template. This stage continues until a termination signal is encountered.

Termination: Transcription concludes when the RNA polymerase reaches a specific termination signal on the DNA. This signal instructs the polymerase to release the newly formed RNA molecule. The DNA double helix reforms, and the RNA product is freed.

RNA Processing

RNA processing is an step in gene expression, particularly in eukaryotes, where the initial RNA transcript (pre-mRNA) undergoes several modifications to become mature mRNA. These modifications include:

1. Capping: To the 5′ end of the pre-mRNA a modified guanosine cap is added to the 5′ end of the pre-mRNA. This cap helps protect the mRNA and it is essential for ribosome binding during translation.
2. Splicing: From the pre-mRNA, Introns (non-coding regions) are removed, and exons (coding regions) are joined together. This process creates the mature mRNA sequence that carries the genetic information for protein synthesis.
3. Polyadenylation: To the 3′ end of the mRNA a poly-A tail, a series of adenine nucleotides, is added. This tail aids in mRNA stability and transport out of the nucleus.

The end product of RNA processing is mature mRNA. It is transported out of the nucleus and serves as a template for protein synthesis at the ribosomes during translation. These processing steps ensure that the genetic information is accurately transcribed and prepared for efficient protein production.

Inhibitor of Transcription

Inhibitors of transcription are molecules or compounds that can interfere with the normal process of transcription. They reduces or preventes the synthesis of RNA from DNA. These inhibitors can have various mechanisms of action, such as blocking the activity of RNA polymerase or disrupting the binding of transcription factors to DNA. Some examples of transcription inhibitors includes:

1. Streptolydigin: By attaching to the polymerase, it prevents the extension of nucleic acid chains, which halts the activity of RNA polymerase within the cell.
2.  Rifampicin (rifamycin): It is a medicine that fights tuberculosis. It prevents mitochondrial RNA polymerase from working by attaching to the beta subunit of bacterial RNA polymerase.
3. Alpha amanitin: It is an isolated eukaryotic inhibitor from Amanita phalloides that prevents the start and elongation of RNA II polymerase.
4. Cordycepin: It demonstrates the absence of the hydroxyl moiety at the 3′ position, which prevents RNA synthesis and transcription elongation.
5. Actinomycin D: Antibiotic has antibacterial and anticancer properties. It prevents rRNA transcription.

Transcription Termination

Until it receives instructions to halt, RNA polymerase will continue to transcribe. Termination, which occurs when the polymerase transcribes a DNA sequence known as a terminator, is the process of stopping transcription. There are two primary methods of transcription termination:

Rho-Dependent Termination: In this mechanism, a protein called Rho factor binds to the newly synthesized RNA and moves along it, eventually catching up to RNA polymerase. The interaction between Rho and RNA polymerase leads to transcription termination.

Rho-Independent (Intrinsic) Termination: In this method, a termination signal on the DNA template strand leads to the formation of a hairpin loop in the newly synthesized RNA. This loop disrupts the RNA-DNA hybrid, causing RNA polymerase to pause and then release the RNA molecule.

Also Read:

• Difference Between Replication And Transcription
• Difference Between Template and Coding Strand
• Molecular Basis of Inheritance Notes Class 12
• RNA Translation
• DNA Replication

FAQs on Transcription

1. What is the process of transcription?

Transcription is the process of copying genetic information from DNA to RNA. It involves RNA polymerase binding to a DNA promoter. It synthesizes a complementary RNA strand using the DNA template, and terminating when it reaches a specific signal.

2. Where the transcription start and terminate?

Transcription starts at the promoter region on the DNA, that is it starts at the 5′-end of the DNA sequence. It marks the beginning of the gene to be transcribed. Transcription terminates when RNA polymerase encounters a specific termination signal on the DNA.

3. What is the End Product of Transcription?

RNA molecule, mainly messenger RNA (mRNA), is the end product of transcription, which carries the genetic code from DNA and serves as a template for protein synthesis during translation.

4. What are the Promoter eSquences?

Promoter sequences are specific DNA regions where RNA polymerase and transcription factors bind to initiate transcription. These are located upstream at the 5′ end of the DNA sequence.

5. Are Enhancers Necessary for Transcription?

Enhancers are not necessary for transcription initiation. They can greatly enhance gene expression by increasing transcription rates. They are regulatory DNA sequences that facilitate precise control of transcription.

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