Genetics: DNA Replication and Gene Regulation
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Questions and Answers

What role do transcriptional activators play in gene expression?

  • They convert DNA directly into RNA without polymerase.
  • They bind to the promoter region and inhibit gene expression.
  • They bind to enhancer sequences and increase gene expression. (correct)
  • They degrade mRNA to prevent transcription.

    • What is the significance of binding transcription factors around the promoter region?

  • They control the rate of gene expression. (correct)
  • They permanently modify the DNA sequence.
  • They exclusively prevent gene activation.
  • They increase the stability of the RNA polymerase molecule.

    • Which enzyme is primarily responsible for the production of mRNAs, tRNAs, and rRNAs?

  • DNA polymerase
  • Ribosome
  • RNA polymerase II (correct)
  • Transcription factor

    • What distinguishes enhancer sequences from promoter regions in gene expression?

    <p>Enhancers can be located far from the promoter and still influence expression.</p> Signup and view all the answers

    In the context of transcription, what is the main function of the mediator complex?

    <p>To facilitate communication between transcription factors and RNA polymerase.</p> Signup and view all the answers

    What process describes how exons can be organized in different combinations to produce various protein isoforms?

    <p>Splicing</p> Signup and view all the answers

    Which of the following correctly defines the relationship between genes and proteins according to Beadle and Tatum's proposal?

    <p>One gene makes one protein.</p> Signup and view all the answers

    What is the consequence of a transcript containing a premature stop codon?

    <p>It generates a truncated protein.</p> Signup and view all the answers

    What is one reason why organisms with similar numbers of genes can exhibit significant differences in complexity?

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

    What characterizes eukaryotic genes compared to prokaryotic genes?

    <p>Eukaryotic genes possess complex regulatory regions.</p> Signup and view all the answers

    Which of the following represents the starting codon in the genetic code?

    <p>AUG codes for methionine.</p> Signup and view all the answers

    What role does non-coding DNA play in the genome?

    <p>It is crucial for organism plasticity and regulation of gene expression.</p> Signup and view all the answers

    Which of the following is NOT typically found in the structure of a human coding gene?

    <p>Ribosomal RNA</p> Signup and view all the answers

    What initiates the transcription of a gene?

    <p>Proteins binding to the promoter region of DNA.</p> Signup and view all the answers

    Why might some genes not be expressed in all cells at all times?

    <p>Gene expression is regulated based on factors such as external stimuli.</p> Signup and view all the answers

    Which stage is NOT a point where gene expression can be regulated?

    <p>Cytoplasmic control</p> Signup and view all the answers

    What is the function of the promoter in gene expression?

    <p>It serves as the binding site for transcription factors.</p> Signup and view all the answers

    In Drosophila melanogaster, why is timing important in gene expression?

    <p>Genes must be activated at specific stages of development.</p> Signup and view all the answers

    What function does the 5' cap of an mRNA serve during translation initiation?

    <p>It helps the ribosome recognize the mRNA.</p> Signup and view all the answers

    Which of the following is NOT a component involved in the elongation phase of translation?

    <p>Cytoplasmic release factors</p> Signup and view all the answers

    What is the main outcome of the translation termination process?

    <p>The ribosome detaches from mRNA.</p> Signup and view all the answers

    What role does the initiator tRNA play in the initiation of translation?

    <p>It recognizes and binds to the start codon.</p> Signup and view all the answers

    What is the significance of alternative splicing in gene expression?

    <p>It allows for the production of multiple proteins from a single gene.</p> Signup and view all the answers

    Which statement about the genetic code is true?

    <p>Each codon corresponds to a single amino acid.</p> Signup and view all the answers

    What happens when a ribosome encounters a stop codon during translation?

    <p>Cytoplasmic release factors bind to the stop codon.</p> Signup and view all the answers

    How does the half-life of mRNA contribute to gene expression regulation?

    <p>By determining how long mRNA is available for translation.</p> Signup and view all the answers

    What is the primary function of the 5’ cap added to the mRNA molecule during transcription?

    <p>To protect the mRNA from degradation</p> Signup and view all the answers

    Which process involves the removal of non-coding regions from the pre-mRNA?

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

    What component is added to the 3’ end of the mRNA during processing?

    <p>Poly-A tail</p> Signup and view all the answers

    Which of the following best describes the role of the WT1 gene?

    <p>It acts as a transcription factor involved in tumor suppression.</p> Signup and view all the answers

    During which stage can gene expression be regulated?

    <p>At transcription, processing, and translation</p> Signup and view all the answers

    Which enzyme is responsible for adding a methylated G nucleotide to the 5’ cap?

    <p>Guananyl transferase</p> Signup and view all the answers

    What is the purpose of the polyadenylation process in RNA processing?

    <p>To provide stability and regulate translation of mRNA</p> Signup and view all the answers

    What type of regions does DNA consist of according to the content?

    <p>Exons and introns</p> Signup and view all the answers

    Study Notes

    DNA Replication

    • Eukaryotic genes differ in structure and function compared to prokaryotic genes.

    Transcriptional Control

    • Gene expression can be regulated at different stages: transcriptional control, processing control (translation), and non-coding DNA.
    • Genes and intergenic regions (non-coding DNA) are important for organism plasticity, control of gene expression.

    Coding Gene Structure

    • Almost all human genes possess a set of similar characteristics:
      • Promoter
      • Transcriptional ‘start’ and ‘stop’ signal
      • Exons and introns
      • Upstream regulatory regions
    • Genes are expressed in various cells depending on signals and stages of the cell cycle.

    Switching a Gene On! Promoter

    • A sequence of DNA that proteins bind to, initiating transcription.
    • Found near the transcription site.

    Switching a Gene On! Transcriptional Activators

    • Gene expression is driven by RNA polymerase II.
    • Transcription factors bind in and around the promoter region, initiating gene expression.
    • Upstream enhancer sequences are also important for fine-tuning gene expression, involving the binding of transcription factors.

    Open Chromatin

    • Open chromatin can be involved in transcription and splicing.

    Transcription Machinery

    • RNA polymerase creates mRNAs, tRNAs, and ribosomal RNA (rRNA).
    • Transcription factors bind to the promoter region, facilitating the activity of RNA polymerase.
    • The WT1 gene is a tumor suppressor gene.

    RNA Processing

    • During transcription, the 5’ end of the mRNA molecule is capped by:
      • Adding a methylated G nucleotide with the help of phosphatase, guananyl transferase, and methyl transferase.
    • The 3’ end is cleaved and a poly-A tail is added by poly-A polymerase.
    • The non-coding regions (introns) are removed from the RNA during splicing.

    RNA Splicing

    • The process of removing introns from RNA to produce mature mRNA that can be translated into proteins.

    Alternative Splicing

    • This process allows for different protein isoforms to be produced from the same gene, leading to greater protein diversity.

    Translational Control

    • mRNA associates with ribosomes in the cytoplasm, translating the RNA sequence into a polypeptide chain (protein).
    • The half-life of mRNA is another way to regulate gene expression levels.

    Translation Initiation

    • Initiator tRNA carrying methionine associates with a small ribosomal unit with initiation factors, starting protein synthesis.
    • The small ribosomal unit recognizes the 5' end of mRNA and scans for the start codon (AUG).

    Translation Elongation

    • The process of adding amino acids to a growing polypeptide chain involves four stages:
      • Aminoacyl-tRNA binds to the A site.
      • Peptide bond formation between the polypeptide chain and the amino acid in the A site.
      • Ribosome moves one codon along the mRNA.
      • The new peptidyl-tRNA in the A site moves to the P site, and the tRNA in the P site becomes the new E site.

    Translation Termination

    • Protein synthesis stops when the ribosome encounters a stop codon (UAA, UAG, UGA).
    • Release factors bind to the stop codon, freeing the growing polypeptide chain.

    One Gene - One Protein Hypothesis

    • Beadle and Tatum proposed that one gene codes for one protein.
    • However, alternative splicing can produce multiple proteins from a single gene.

    Alternative Splicing

    • Exons can be joined together in various ways during splicing, leading to different proteins from a single gene.

    Isoforms

    • Alternative mRNAs of a single gene can produce various protein isoforms.

    Translation

    • The process of translating the genetic code in mRNA into the amino acid sequence of a protein.

    Premature Stop Signals and In-Frame Stop Signals

    • These alterations can lead to the production of truncated protein products, which may not function normally.

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    Description

    This quiz delves into the intricacies of DNA replication and gene regulation in eukaryotic organisms. Explore key concepts such as gene structure, transcriptional control, and the roles of promoters and transcription factors. Test your understanding of how genes are expressed and regulated in response to various signals.

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