Gene Expression in Eukaryotic Cells
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Questions and Answers

What is the role of TFIID in the formation of the transcription initiation complex?

  • To distort DNA locally and permit binding of TFIIB (correct)
  • To hydrolyze ATP during transcription initiation
  • To load elongation factors onto RNA polymerase
  • To release RNA polymerase from general transcription factors

    • What triggers the release of RNA polymerase from general transcription factors?

  • Hydrolysis of ATP by TFIIH
  • Dissociation of TFIID from the DNA
  • Phosphorylation of RNA polymerase's polypeptide tail (correct)
  • Binding of elongation factors to RNA polymerase

    • What is the consequence of TFIIH's action at the transcription start site?

  • It binds directly to RNA polymerase to initiate transcription
  • It exposes the template strand of DNA by separating the double helix (correct)
  • It catalyzes the formation of the transcription bubble
  • It stabilizes the transcription initiation complex

    • Which statement is true regarding TFIID's role during transcription initiation?

    <p>TFIID remains bound after initiating transcription</p> Signup and view all the answers

    Which factor is primarily responsible for loading elongation factors onto RNA polymerase?

    <p>The phosphorylated polypeptide tail of RNA polymerase</p> Signup and view all the answers

    What do gene activators primarily do during transcription initiation?

    <p>Enhance efficiency by recruiting enzymes that modify histone proteins</p> Signup and view all the answers

    What is the role of gene repressors in transcription initiation?

    <p>Recruit enzymes that modify histone proteins, inhibiting transcription</p> Signup and view all the answers

    How does chromatin structure impact transcription initiation?

    <p>It physically blocks the assembly of transcription initiation complexes on the promoter</p> Signup and view all the answers

    In multicellular organisms, how do distinct cell types express different proteins despite having the same DNA?

    <p>By differing in sets of genes or proteins that are expressed</p> Signup and view all the answers

    What effect do enzymes like HATs (histone acetyltransferases) have on transcription?

    <p>They modify histones to allow easier access for transcription factors</p> Signup and view all the answers

    What is essential for the export of mRNA to the cytosol?

    <p>Binding with poly-A-binding proteins and a cap-binding complex</p> Signup and view all the answers

    What role does the nuclear pore complex play in cellular processes?

    <p>It controls the entry and exit of macromolecules from the nucleus.</p> Signup and view all the answers

    Which statement accurately describes transcription regulators?

    <p>They recognize specific regulatory DNA sequences.</p> Signup and view all the answers

    How can gene activation occur from a distance?

    <p>Through the looping of intervening DNA sequences.</p> Signup and view all the answers

    What happens to waste RNAs in the nucleus?

    <p>They remain in the nucleus and can be reused for transcription.</p> Signup and view all the answers

    What is the primary function of repressor proteins in transcription?

    <p>They inhibit transcription by preventing TIC assembly.</p> Signup and view all the answers

    What type of interactions do transcription regulators form with regulatory DNA sequences?

    <p>Specific non-covalent interactions</p> Signup and view all the answers

    Which of the following is NOT a type of RNA typically remaining in the nucleus?

    <p>mRNA bound for translation</p> Signup and view all the answers

    What role do elongation factors play during RNA synthesis?

    <p>They facilitate the movement of RNA Polymerase through nucleosomes.</p> Signup and view all the answers

    What event occurs when RNA Polymerase finishes transcription?

    <p>RNA Polymerase is released from the DNA.</p> Signup and view all the answers

    Which nucleotide triphosphates are involved in ribonucleotide synthesis during transcription?

    <p>ATP, CTP, UTP, and GTP</p> Signup and view all the answers

    What process occurs simultaneously with RNA synthesis to form mRNA?

    <p>Capping and polyadenylation occur.</p> Signup and view all the answers

    What modification is made at the 5’ end of RNA during RNA capping?

    <p>Attachment of a guanine nucleotide bearing a methyl group.</p> Signup and view all the answers

    What drives the overall reaction of polynucleotide synthesis during RNA synthesis?

    <p>Hydrolysis of the pyrophosphate.</p> Signup and view all the answers

    What is the purpose of polyadenylation in mRNA processing?

    <p>Adding repeated adenine nucleotides to the 3’ end.</p> Signup and view all the answers

    Which enzymes are primarily responsible for capping and polyadenylation of mRNA?

    <p>Different enzymes present on the phosphorylated tail of RNA Polymerase.</p> Signup and view all the answers

    What role do transcription regulators play in gene expression?

    <p>They direct the assembly of a complete transcription initiation complex.</p> Signup and view all the answers

    How does alternative splicing benefit eukaryotic cells?

    <p>It allows production of different proteins from the same gene.</p> Signup and view all the answers

    What is one of the mechanisms that fine-tune gene expression in eukaryotic cells after transcription initiation?

    <p>Alternative RNA splicing.</p> Signup and view all the answers

    What determines the transcription rate of a gene in eukaryotic cells?

    <p>The integration of various signals through regulatory DNA sequences.</p> Signup and view all the answers

    Which of the following is NOT a mechanism of mRNA degradation control?

    <p>Alternative RNA splicing.</p> Signup and view all the answers

    What is the significance of the 5' cap and poly-A tail in RNA?

    <p>They protect mRNA and enhance translation efficiency.</p> Signup and view all the answers

    What is the primary purpose of capping and polyadenylation of mRNA?

    <p>To increase stability of mRNA and facilitate export to cytosol</p> Signup and view all the answers

    What can a single protein accomplish in terms of gene expression?

    <p>It can coordinate the expression of multiple genes.</p> Signup and view all the answers

    What is meant by combinatorial control in gene expression?

    <p>The interaction of multiple transcription regulators to control gene expression.</p> Signup and view all the answers

    Which sequences are transcribed into the RNA transcript of eukaryotic genes?

    <p>Both exons and introns</p> Signup and view all the answers

    What role do snRNAs play in the spliceosome during RNA splicing?

    <p>They catalyze the splicing reactions and form covalent bonds between exons</p> Signup and view all the answers

    How are introns removed during RNA splicing?

    <p>By forming a lariat structure that is then degraded in the nucleus</p> Signup and view all the answers

    What is indicated by successful splicing in pre-mRNA?

    <p>The presence of exon junction complexes</p> Signup and view all the answers

    What is the main function of splice site sequences in pre-mRNA?

    <p>To indicate the beginning and end of introns</p> Signup and view all the answers

    What ensures that mRNA export from the nucleus is selective?

    <p>Capping and polyadenylation modifications</p> Signup and view all the answers

    What is the primary characteristic of exons in eukaryotic genes?

    <p>They are short protein-coding sequences that are scattered throughout the gene</p> Signup and view all the answers

    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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    SBP3411 Gene Expression in Eukaryotic Cells PDF Lecture Notes

    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.

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