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Questions and Answers
What is the role of TFIID in the formation of the transcription initiation complex?
What is the role of TFIID in the formation of the transcription initiation complex?
What triggers the release of RNA polymerase from general transcription factors?
What triggers the release of RNA polymerase from general transcription factors?
What is the consequence of TFIIH's action at the transcription start site?
What is the consequence of TFIIH's action at the transcription start site?
Which statement is true regarding TFIID's role during transcription initiation?
Which statement is true regarding TFIID's role during transcription initiation?
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Which factor is primarily responsible for loading elongation factors onto RNA polymerase?
Which factor is primarily responsible for loading elongation factors onto RNA polymerase?
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What do gene activators primarily do during transcription initiation?
What do gene activators primarily do during transcription initiation?
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What is the role of gene repressors in transcription initiation?
What is the role of gene repressors in transcription initiation?
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How does chromatin structure impact transcription initiation?
How does chromatin structure impact transcription initiation?
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In multicellular organisms, how do distinct cell types express different proteins despite having the same DNA?
In multicellular organisms, how do distinct cell types express different proteins despite having the same DNA?
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What effect do enzymes like HATs (histone acetyltransferases) have on transcription?
What effect do enzymes like HATs (histone acetyltransferases) have on transcription?
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What is essential for the export of mRNA to the cytosol?
What is essential for the export of mRNA to the cytosol?
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What role does the nuclear pore complex play in cellular processes?
What role does the nuclear pore complex play in cellular processes?
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Which statement accurately describes transcription regulators?
Which statement accurately describes transcription regulators?
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How can gene activation occur from a distance?
How can gene activation occur from a distance?
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What happens to waste RNAs in the nucleus?
What happens to waste RNAs in the nucleus?
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What is the primary function of repressor proteins in transcription?
What is the primary function of repressor proteins in transcription?
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What type of interactions do transcription regulators form with regulatory DNA sequences?
What type of interactions do transcription regulators form with regulatory DNA sequences?
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Which of the following is NOT a type of RNA typically remaining in the nucleus?
Which of the following is NOT a type of RNA typically remaining in the nucleus?
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What role do elongation factors play during RNA synthesis?
What role do elongation factors play during RNA synthesis?
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What event occurs when RNA Polymerase finishes transcription?
What event occurs when RNA Polymerase finishes transcription?
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Which nucleotide triphosphates are involved in ribonucleotide synthesis during transcription?
Which nucleotide triphosphates are involved in ribonucleotide synthesis during transcription?
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What process occurs simultaneously with RNA synthesis to form mRNA?
What process occurs simultaneously with RNA synthesis to form mRNA?
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What modification is made at the 5’ end of RNA during RNA capping?
What modification is made at the 5’ end of RNA during RNA capping?
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What drives the overall reaction of polynucleotide synthesis during RNA synthesis?
What drives the overall reaction of polynucleotide synthesis during RNA synthesis?
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What is the purpose of polyadenylation in mRNA processing?
What is the purpose of polyadenylation in mRNA processing?
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Which enzymes are primarily responsible for capping and polyadenylation of mRNA?
Which enzymes are primarily responsible for capping and polyadenylation of mRNA?
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What role do transcription regulators play in gene expression?
What role do transcription regulators play in gene expression?
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How does alternative splicing benefit eukaryotic cells?
How does alternative splicing benefit eukaryotic cells?
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What is one of the mechanisms that fine-tune gene expression in eukaryotic cells after transcription initiation?
What is one of the mechanisms that fine-tune gene expression in eukaryotic cells after transcription initiation?
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What determines the transcription rate of a gene in eukaryotic cells?
What determines the transcription rate of a gene in eukaryotic cells?
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Which of the following is NOT a mechanism of mRNA degradation control?
Which of the following is NOT a mechanism of mRNA degradation control?
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What is the significance of the 5' cap and poly-A tail in RNA?
What is the significance of the 5' cap and poly-A tail in RNA?
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What is the primary purpose of capping and polyadenylation of mRNA?
What is the primary purpose of capping and polyadenylation of mRNA?
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What can a single protein accomplish in terms of gene expression?
What can a single protein accomplish in terms of gene expression?
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What is meant by combinatorial control in gene expression?
What is meant by combinatorial control in gene expression?
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Which sequences are transcribed into the RNA transcript of eukaryotic genes?
Which sequences are transcribed into the RNA transcript of eukaryotic genes?
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What role do snRNAs play in the spliceosome during RNA splicing?
What role do snRNAs play in the spliceosome during RNA splicing?
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How are introns removed during RNA splicing?
How are introns removed during RNA splicing?
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What is indicated by successful splicing in pre-mRNA?
What is indicated by successful splicing in pre-mRNA?
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What is the main function of splice site sequences in pre-mRNA?
What is the main function of splice site sequences in pre-mRNA?
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What ensures that mRNA export from the nucleus is selective?
What ensures that mRNA export from the nucleus is selective?
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What is the primary characteristic of exons in eukaryotic genes?
What is the primary characteristic of exons in eukaryotic genes?
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Study Notes
Gene Expression in Eukaryotic Cells
- This lecture covers gene expression in eukaryotic cells
- Students will learn about the role of different RNA molecules in eukaryotic gene expression
- They will also learn about the key events and molecules involved in RNA synthesis and processing.
- The role of transcription regulators in eukaryotic gene expression will be discussed.
- Examples of post-transcriptional control mechanisms at various levels will be presented.
Lecture Outline
- Types of RNA & RNA polymerases: Details about different types of RNA and their functions. RNA polymerases and their roles will be covered.
- RNA synthesis and processing: This section will cover RNA synthesis and processing in eukaryotic cells.
- Transcriptional controls: This will cover the details on how transcription is controlled in eukaryotic cells.
- Post-transcriptional controls: Details of post-transcriptional control mechanisms in eukaryotic cells.
DNA Organization in Eukaryotic Cells
- DNA stores hereditary information
- All cells in a multicellular organism have the same DNA content.
- Eukaryotic DNA is packaged into multiple chromosomes.
- Chromosome packing occurs on multiple levels, compacting the DNA significantly.
- High levels of DNA organization prevent entanglement while keeping DNA accessible for replication, repair, and gene expression.
Flow of Genetic Information
- Genetic information flows from DNA to RNA (transcription) and then to protein (translation).
- DNA contains the instructions for making proteins.
- Transcription copies the DNA code into RNA.
- Translation translates the RNA code into a protein.
- RNA molecules play important roles in this process.
- DNA can be copied or replicated.
- The segments of DNA that are transcribed to RNA are called genes (orange).
RNA Transcripts or Molecules
- RNA carries genetic information from DNA, utilizing different chemical forms (e.g., ribose vs. deoxyribose).
- RNA is single-stranded, unlike its DNA counterpart (in most cases).
- RNA polymerase unwinds DNA to catalyze nucleotide joining.
- Different types of RNA have specific functions in cells. (e.g., messenger RNA, ribosomal RNA, transfer RNA...).
RNA Synthesis in Eukaryotic Cells: Initiation
- General transcription factors (TFs) assemble on the promoter region.
- The promoter is a DNA sequence upstream of the gene.
- RNA polymerase II is oriented on the promoter to start transcription in the correct direction.
- The order of TF binding can vary between promoters.
- TFIID binds to the TATA box, which is frequently found upstream of promoters used by RNA polymerase II.
- Adjacent binding of TFIIB occurs due to DNA distortion caused by TFIID.
RNA Synthesis: Formation of Transcription Initiation Complex
- General TFs are assembled to initiate transcription.
- TFIIH opens the DNA helix at the transcription start site.
- RNA polymerase II binding completes the initiation complex.
- RNA polymerase II must be released from general TFs to begin transcription.
- TFIIH phosphorylates the RNA polymerase II tail. -Dissociated general TFs can initiate transcription with other RNA polymerases.
RNA Synthesis: Elongation & Termination
- RNA polymerase moves along DNA to unwind the DNA helix.
- Polynucleotide synthesis is driven by ATP hydrolysis.
- Incoming ribonucleotides are added to the 3' end of the growing RNA chain.
- Pyrophosphate hydrolysis drives the overall reaction.
- The RNA polymerase tail is dephosphorylated to release the enzyme from the DNA.
Eukaryotic RNA Processing: RNA Capping & Polyadenylation
- RNA processing occurs as RNA is synthesized.
- RNA capping involves adding a modified guanine nucleotide to the 5' end.
- Polyadenylation adds a poly(A) tail to the 3' end.
- These processes increase mRNA stability and facilitate export from the nucleus.
- Enzymes are present on the phosphorylated tail of RNA polymerase that facilitate these changes.
Organization of Eukaryotic Genes and pre-mRNA
- Exons are the coding sections of genes (fragments).
- Introns are non-coding sections of genes that are removed in RNA processing.
- RNA splicing removes introns and joins exons.
- This occurs after capping but before polyA tail addition.
- Spliced pre-mRNA is ready to be translated.
RNA Splicing by Spliceosome
- Spliceosomes are composed of snRNAs and proteins.
- snRNAs catalyze splicing reactions and form bonds between exons.
- Exons are stitched together after the introns are removed.
- Introns are either degraded or used in other cellular processes.
mRNA Export
- Correctly processed mRNA is exported from the nucleus to the cytosol.
- This is facilitated by proteins that bind to mRNA.
- Nuclear pores facilitate mRNA transport.
- Unprocessed mRNA and other RNAs are degraded in the nucleus.
Gene Expression is Mainly Controlled by Transcription Regulators
- Transcription regulators switch transcription 'on' (activators) or 'off' (repressors).
- These proteins bind to specific DNA sequences.
- Gene activation can occur at long distances through DNA looping.
- Repressors prevent transcription initiation.
Transcription Regulators Recruit Chromatin-Modifying Proteins
- DNA packaging (nucleosomes) can block initiation.
- Proteins modify chromatin structure to allow access.
- Activator proteins enhance transcription initiation via recruitment of chromatin-modifying enzymes (e.g., HATs).
- Repressor proteins hinder transcription initiation ( e.g., HDACS).
Transcriptional Control in a Multicellular Organism
- Cells in a multicellular organism express unique sets of genes, determined by transcription regulators.
- Combined action of different transcription factors leads to specific changes in transcription rates.
- Regulatory DNA sequences integrate signals to activate or repress transcription.
- Certain genes are constitutively present across all cell types.
Post-transcriptional Controls in Eukaryotic Cells
- Mechanisms that regulate gene expression after initiation.
- Alternative splicing, mRNA degradation, and translation control.
- mRNA stability varies based on nucleotide sequences that may or may not contain binding sites for degradation proteins.
- Proteins modify mRNA, potentially preventing translation or initiating degradation.
- miRNA- mediated mechanisms are present, affecting mRNA degradation.
Alternative Splicing of RNA in Eukaryotic Cells
- Exons can be skipped or included in mRNA, leading to multiple mRNAs from a single gene.
- This allows for a larger variety of proteins from a limited DNA sequence.
Mechanisms of mRNA Degradation Control
- mRNA lifetime determines protein levels.
- Short-lived mRNA usually results in lower protein levels.
- mRNA with sequences containing binding sites for proteins that facilitate degradation are destroyed.
- Degradation controlled by specific proteins or via mRNA modification.
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Description
This quiz explores gene expression specifically in eukaryotic cells. Students will learn about the various RNA types, their roles in RNA synthesis and processing, and the mechanisms of transcriptional and post-transcriptional control. Key concepts regarding transcription regulators and their influence on gene expression will also be examined.
