Questions and Answers
What is the role of the sigma factor in E. coli transcription initiation?
What is the outcome of RNA polymerase binding tightly to the DNA in the promoter region?
Why does RNA polymerase not recognize a -10/-35 sequence as a promoter region?
What is the unique function of RNA polymerase that DNA polymerase lacks?
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What happens to the sigma factor after the addition of about 10 nucleotides?
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In which direction does RNA polymerase synthesize RNA during transcription elongation?
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What is the role of the -35 and -10 elements in E. coli transcription initiation?
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What is the term for the process of RNA polymerase synthesizing RNA by joining two dNTPs together and hydrogen bonding them to the template at the +1 site?
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During translation initiation, what event triggers the release of various initiation factors (eIFs) from the ribosome?
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What is the function of elongation factor 1a (eEF1⍺) during translation elongation?
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Which of the following is NOT directly involved in the initiation of translation in eukaryotic cells?
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What is the role of the small ribosomal subunit during translation initiation?
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How does the ribosome move one codon down the mRNA during translation elongation?
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Which of the following best describes the role of a release factor in translation termination?
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Which of the following is NOT a key player in the translation initiation complex in eukaryotic cells?
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How does heme regulate translation initiation?
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What sequence is indicative of transcription termination in bacteria?
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In eukaryotic cells, how many types of RNA polymerase are present?
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What role does the poly U sequence play in transcription termination?
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Which of the following describes the transcription process in prokaryotes?
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What is the primary function of the sigma factor in prokaryotic transcription?
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What occurs during the transcription elongation phase?
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Which factor directly influences the rate of transcription initiation in eukaryotic cells?
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What happens to RNA polymerase once elongation is complete?
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Study Notes
Transcription Initiation in E. coli
- RNA polymerase initially binds non-specifically to DNA, assisted by the sigma factor.
- The sigma factor locates conserved -35 and -10 promoter elements; recognition of both is essential for initiating transcription.
- Formation of a closed promoter complex precedes DNA unwinding, creating an open promoter complex allowing initiation.
- The +1 site marks the transcription start point where RNA polymerase synthesizes RNA de novo, a capability unique to RNA polymerases.
- DNA polymerases can only elongate existing strands, not initiate synthesis.
Transcription Elongation
- Sigma factor is released after approximately 10 nucleotides are added, allowing RNA polymerase to progress along the DNA template.
- RNA polymerase synthesizes RNA in the 5' to 3' direction, using the 3' to 5' strand as a template.
- Poly(A) Binding Proteins (PABP) interact with mRNA to bring together its 5' and 3' ends.
Translation Initiation in Eukaryotes
- Initiation begins with the small ribosomal subunit scanning mRNA for the first AUG codon in the 5' to 3' direction.
- eIF5 stimulates hydrolysis of GTP bound to eIF2; phosphorylation of eIF2 by Heme-regulated inhibitor kinase (HRI) prevents GDP release and ceases further translation.
- Release of eIFs occurs upon GTP hydrolysis, allowing the large ribosomal subunit to bind.
Translation Elongation
- Elongation Factor 1a (eEF1⍺) facilitates the entry of tRNA bound to GTP into the ribosome's A site.
- The presence of the correct tRNA triggers GTP hydrolysis and formation of a peptide bond, followed by ribosome movement along the mRNA.
Translation Termination
- Encountering a STOP codon prompts a release factor to bind at the ribosomal A site.
- Binding of the release factor leads to hydrolysis of the tRNA-polypeptide bond, culminating in dissociation of the ribosome and mRNA from the newly synthesized polypeptide.
Transcription Termination in Prokaryotes
- A termination signal, typically a symmetrical inverted repeat of GC-rich sequences followed by a poly(A) tail, marks the end of transcription.
- RNA polymerase synthesizes RNA through the GC-rich region, which forms a hairpin structure, promoting dissociation of the RNA polymerase.
- The poly(U) sequence enhances the release of RNA from the template.
Eukaryotic Transcription Overview
- Eukaryotes possess four RNA polymerases (I, II, III, and mitochondrial) for various RNA types, contrasting with prokaryotes’ single RNA polymerase.
- Mitochondrial RNA polymerase resembles bacterial RNA polymerase more than eukaryotic counterparts.
- Rifampicin, an antibiotic, inhibits bacterial RNA polymerase and high doses can affect mitochondrial transcription too.
Regulation of Transcription Initiation
- Both prokaryotic and eukaryotic transcription are closely regulated; this regulation is crucial for overall cell function.
- Transcription initiation in eukaryotes involves complex interactions, including RNA polymerase II and mediator complexes.
RNA Processing in Eukaryotes
- Eukaryotic RNA undergoes extensive processing after transcription, which is critical for functional RNA production.
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Description
Understand the process of transcription initiation in E. coli, including the role of RNA polymerase, sigma factor, and promoter elements.
