7.Eukaryotic gene transcription, its steps, enzymes involved in its mechanism
Eukaryotic gene transcription is the process by which the genetic information encoded in the DNA is transcribed into a complementary RNA molecule. This RNA molecule can then be used to synthesize proteins through the process of translation. The steps and enzymes involved in eukaryotic gene transcription include:
1. Initiation:
- RNA Polymerase II (RNAP II): This enzyme recognizes the promoter sequence on the DNA and binds to it, along with various transcription factors.
- Transcription Factors: These proteins help recruit and position the RNAP II complex at the promoter region.
2. Promoter clearance:
- TFIIH: This transcription factor complex unwinds the DNA double helix near the promoter region, which allows the RNAP II complex to begin transcribing the DNA template.
3. Elongation:
- RNAP II: Once the RNA polymerase complex is properly positioned and the DNA strand is unwound, RNAP II begins synthesizing the RNA molecule using the DNA template strand as a guide.
- NTPs (nucleoside triphosphates): These are the building blocks of the RNA molecule and are added sequentially to the growing RNA chain.
4. Termination:
- Termination signal: After the RNA polymerase has transcribed the entire gene, a termination signal is encountered, which causes the release of the RNA polymerase from the DNA template.
- Termination factors: These proteins help in the recognition and binding of termination signals, facilitating the termination of transcription.
It is important to note that eukaryotic gene transcription is a complex process that involves the interplay of multiple proteins and regulatory elements. Additionally, various post-transcriptional modifications, such as RNA splicing and processing, can occur to produce a mature RNA molecule before it is exported from the nucleus for translation.
Gene transcription is the process by which the information encoded in a gene is used to synthesize a functional RNA molecule. In eukaryotic cells, this process occurs in the nucleus and involves several steps and enzymes.
1. Initiation: Transcription begins with the binding of transcription factors to specific DNA sequences called promoter regions. These transcription factors recruit an enzyme called RNA polymerase II, which is responsible for synthesizing the RNA molecule. The RNA polymerase II forms a complex with other proteins, forming the transcription initiation complex.
2. Promoter clearance: Once the transcription initiation complex is formed, RNA polymerase II unwinds the DNA helix and initiates the synthesis of an RNA molecule using one of the DNA strands (the template strand) as a template. As the RNA polymerase moves along the DNA, it adds complimentary RNA nucleotides to form a growing RNA molecule.
3. Elongation: During elongation, RNA polymerase continues to move along the DNA template strand, synthesizing the RNA molecule in a 5' to 3' direction. This involves the addition of RNA nucleotides to the growing RNA chain.
4. Termination: At the end of the gene, specific DNA sequences called terminator regions signal the termination of transcription. The RNA polymerase dissociates from the DNA template strand, and the newly formed RNA molecule is released.
Enzymes Involved:
1. RNA polymerase II: This is the main enzyme responsible for synthesizing the RNA molecule during eukaryotic gene transcription. It catalyzes the addition of RNA nucleotides based on the DNA template.
2. Transcription factors: These are protein molecules that bind to specific DNA sequences called promoter regions, which are necessary for the initiation of transcription. They recruit RNA polymerase II to the promoter and help regulate gene expression.
In summary, eukaryotic gene transcription involves the steps of initiation, promoter clearance, elongation, and termination. The main enzyme involved in this process is RNA polymerase II, along with transcription factors that assist in the regulation and initiation of transcription.
what is the main difference between prokaryotic transcription and eukaryotic transcription
The main difference between prokaryotic and eukaryotic transcription lies in the complexity of the process and the regulatory mechanisms involved. Here are some key differences:
1. Compartmentalization: In prokaryotes, transcription occurs in the cytoplasm since there is no nuclear membrane to separate the DNA from the rest of the cellular components. In eukaryotes, transcription mainly takes place in the nucleus, where the DNA is housed.
2. Gene Structure: Prokaryotes typically have genes that consist of a coding region, referred to as the operon, without introns. In contrast, eukaryotic genes are more complex, usually containing introns (non-coding regions) that need to be removed by mechanisms such as RNA splicing.
3. Transcription Factors: Prokaryotes have fewer transcription factors involved in gene regulation. Eukaryotes, on the other hand, have a more elaborate system of transcription factors that control gene expression by binding to specific regions on the DNA and recruiting RNA polymerase II.
4. Promoter Recognition: Prokaryotic transcription primarily relies on a specific DNA sequence called the promoter, typically found upstream of the coding region. Eukaryotic transcription, however, involves the recognition of more complex promoter sequences that are recognized by multiple transcription factors.
5. RNA Polymerase: Prokaryotes generally have a single RNA polymerase enzyme responsible for transcription. Eukaryotes have multiple RNA polymerases: RNA polymerase I transcribes ribosomal RNA genes, RNA polymerase II transcribes protein-coding genes, and RNA polymerase III transcribes transfer RNA genes and other small functional RNAs.
6. Post-Transcriptional Modifications: Eukaryotic transcription involves extensive post-transcriptional modifications of the initial RNA molecules. These include 5' capping, 3' polyadenylation, and RNA splicing to remove introns and join exons together. Prokaryotic transcription does not typically involve these modifications.
The differences in transcription between prokaryotes and eukaryotes reflect the complexity and diversity of gene regulation in eukaryotic organisms.
Eukaryotic gene transcription is a process where genetic information in the form of DNA is converted into RNA. This process occurs in the nucleus of eukaryotic cells and consists of several steps, each involving specific enzymes. Here are the steps involved in eukaryotic gene transcription and the enzymes associated with each step:
Step 1: Initiation
- RNA polymerase II (RNAP II) binds to the promoter region of the gene. Promoters are specific DNA sequences that signal the starting point for transcription.
- Transcription factors, such as the TATA-binding protein (TBP), help recruit and position RNAP II at the promoter.
Step 2: Promoter Clearance
- RNAP II undergoes a series of conformational changes to achieve a stable initiation complex.
- Proteins called elongation factors assist in the transition of RNAP II from initiation to elongation.
Step 3: Elongation
- RNAP II moves along the DNA template strand, unwinding it and synthesizing an RNA molecule in the 5' to 3' direction.
- Nucleoside triphosphates (NTPs) serve as substrates for RNA synthesis.
Step 4: Termination
- Two mechanisms are involved in transcription termination: the polyadenylation signal and termination signal.
- Polyadenylation signal: A specific sequence is transcribed, leading to the addition of a poly(A) tail at the 3' end of the RNA transcript. This process is catalyzed by enzymes such as poly(A) polymerase.
- Termination signal: When a termination signal is encountered, RNAP II and the nascent RNA dissociate from the DNA template.
Step 5: RNA Processing
- Newly transcribed pre-mRNA undergoes several modifications before it can be considered a mature mRNA.
- Capping: A modified 7-methylguanosine cap is added to the 5' end of the mRNA. This modified cap helps in mRNA stability and translation initiation.
- Splicing: Introns, non-coding regions within the pre-mRNA, are removed, and exons, the coding regions, are joined together. This process is catalyzed by a complex called the spliceosome.
- Polyadenylation: A poly(A) tail is added to the 3' end of the pre-mRNA. This process is important for stabilizing the mRNA and determines its lifespan.
It's important to note that while RNA polymerase II is the main enzyme involved in transcription, various other proteins and factors participate in the overall process to ensure accurate and efficient gene expression in eukaryotes.