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Questions and Answers

What is the primary function of the polyadenylation signal in mRNA?

  • It enhances stability and facilitates export from the nucleus. (correct)
  • It regulates when and where transcription occurs.
  • It ensures proper intron removal during splicing.
  • It codes for amino acids after splicing.

    • Which component of a gene is primarily responsible for coding for amino acids?

  • Promoter
  • Introns
  • Exons (correct)
  • 3' UTR

    • How do the 5' UTR and 3' UTR regions influence gene expression?

  • They both code for proteins.
  • They enhance transcription initiation.
  • They are non-coding and have no effect on gene expression.
  • They influence translation efficiency and mRNA stability. (correct)

    • Which sequence is part of the conserved elements in a prokaryotic promoter region?

    <p>-10 Box (C)</p> Signup and view all the answers

    What role do introns play within a gene structure?

    <p>They may assist in gene regulation and alternative splicing. (C)</p> Signup and view all the answers

    What is the significance of the Shine-Dalgarno sequence in prokaryotic genes?

    <p>It aligns the ribosome for translation initiation. (B)</p> Signup and view all the answers

    What is the main difference between prokaryotic and eukaryotic gene structures?

    <p>Eukaryotic genes contain introns and exons, while prokaryotic genes usually do not. (A)</p> Signup and view all the answers

    What function does the promoter serve in gene expression?

    <p>It regulates when and where transcription occurs. (B)</p> Signup and view all the answers

    What is the start codon in the coding sequence of a gene?

    <p>AUG (C)</p> Signup and view all the answers

    What is the main function of the promoter in gene structure?

    <p>To initiate transcription by providing binding sites for RNA polymerase (C)</p> Signup and view all the answers

    Which feature characterizes a rho-independent terminator region in transcription?

    <p>Contains a hairpin loop followed by uracils (A)</p> Signup and view all the answers

    Which of the following best describes an open reading frame (ORF)?

    <p>A continuous stretch of nucleotides starting with a start codon and ending with a stop codon (A)</p> Signup and view all the answers

    Which of the following describes an operon?

    <p>Multiple genes transcribed from a single promoter (D)</p> Signup and view all the answers

    What is the typical signature sequence of a eukaryotic promoter region?

    <p>5' - TATAAAA - 3' (A)</p> Signup and view all the answers

    What do eukaryotic genes contain that prokaryotic genes typically do not?

    <p>Introns (C)</p> Signup and view all the answers

    How does the coding sequence (CDS) function in a gene?

    <p>It gets translated into protein (D)</p> Signup and view all the answers

    What role do exons play in the processing of mRNA?

    <p>They are coding sequences that remain in mature mRNA (B)</p> Signup and view all the answers

    Which statement accurately describes introns?

    <p>They are non-coding sequences spliced out from pre-mRNA (A)</p> Signup and view all the answers

    What sequence elements are inherent in the core promoter of eukaryotic genes?

    <p>5'-TATAA-3' TATA box (C)</p> Signup and view all the answers

    Which type of terminators signal the end of transcription in prokaryotic genes?

    <p>Both Rho-dependent and Rho-independent terminators (A)</p> Signup and view all the answers

    What marks the 5' splice site of an intron?

    <p>5' - GU - 3' (C)</p> Signup and view all the answers

    What is the function of the Rho protein in transcription termination?

    <p>It helps terminate transcription at rho-dependent sites (C)</p> Signup and view all the answers

    What aspect distinguishes the 5' untranslated region (UTR) in eukaryotic genes?

    <p>It influences the efficiency of translation (C)</p> Signup and view all the answers

    What distinguishes the codon in the coding region of a gene?

    <p>Codons dictate the amino acid sequence of the resulting protein (B)</p> Signup and view all the answers

    What role does the 5' UTR play in gene regulation?

    <p>It contains sequences that affect translation efficiency. (A)</p> Signup and view all the answers

    Which of the following describes enhancers in gene expression?

    <p>They can increase transcription from a distance. (C)</p> Signup and view all the answers

    What is the DNA signature for the polyadenylation signal in eukaryotic genes?

    <p>AAUAAA (B)</p> Signup and view all the answers

    What is the primary function of the 3' UTR in mRNA?

    <p>To influence mRNA stability and localization. (B)</p> Signup and view all the answers

    Which sequence is characteristic of eukaryotic promoters?

    <p>TATAAAA (D)</p> Signup and view all the answers

    Which of the following is NOT typically found in prokaryotic gene structure?

    <p>Intron sequences (C)</p> Signup and view all the answers

    What is the effect of silencer elements on gene expression?

    <p>They suppress gene expression. (B)</p> Signup and view all the answers

    Which statement about the ribosome binding site in prokaryotes is correct?

    <p>It includes the Shine-Dalgarno sequence. (D)</p> Signup and view all the answers

    Study Notes

    Gene Structure and Function

    • A gene is a segment of DNA that provides instructions for creating proteins or functional RNA molecules.
    • Genes are fundamental units of heredity, meaning they are passed down from parents to offspring.
    • Genes can undergo mutations (changes in DNA sequence) and recombination (exchange of genetic material).

    Coding Sequence (CDS)

    • The CDS is the portion of a gene that is translated into a protein.
    • It starts with a start codon (AUG) and ends with a stop codon (UAA, UAG, or UGA).
    • The CDS contains specific nucleotide sequences that determine the order of amino acids in the protein.

    Open Reading Frame (ORF)

    • An ORF is a continuous stretch of nucleotides within DNA that potentially codes for a protein.
    • An ORF starts with a start codon and ends with a stop codon.
    • Not all ORFs correspond to functional proteins.

    Prokaryotic Gene Structure

    • Prokaryotic genes are relatively simple and organized into operons.
    • Promoter: This region located upstream of the coding region controls the initiation of transcription.
      • It contains conserved sequences:
        • -10 region (Pribnow box): 5'-TATAAT-3'
        • -35 region: 5'-TTGACA-3'
    • Coding Region: This region codes for the protein and does not contain introns.
      • It starts with a start codon (AUG) and ends with a stop codon (UAA, UAG, or UGA).
    • Terminator: This sequence signals the end of transcription, ensuring proper regulation.
      • It can be Rho-dependent or Rho-independent.

    Eukaryotic Gene Structure

    • Eukaryotic genes are more complex than prokaryotic genes, containing several distinct elements.
    • Promoter:
      • Core Promoter: Recognized by RNA polymerase, often containing the TATA box (5'-TATAA-3').
      • Proximal Promoter: Contains binding sites for regulatory elements.
      • Distal Promoter: Further upstream with additional regulatory elements.
    • Exons and Introns:
      • Exons: Coding sequences that remain in the mature mRNA after splicing.
      • Introns: Non-coding sequences that are spliced out of pre-mRNA.
      • Signature sequences:
        • Splice donor sites: 5'-GU-3' at the beginning of introns.
        • Splice acceptor sites: 5'-AG-3' at the end of introns.
    • 5' Untranslated Region (UTR):
      • The region upstream of the coding sequence that can influence translation efficiency.
    • 3' Untranslated Region (UTR):
      • The region downstream of the coding sequence that plays roles in mRNA stability and translation regulation.
    • Polyadenylation Signal:
      • A sequence (typically AAUAAA) that signals the addition of a poly-A tail to mRNA, enhancing stability and export from the nucleus.

    Prokaryotic Gene Structure - DNA Signatures

    • Promoter Region:
      • Key Elements: The promoter region in prokaryotes contains two conserved sequences:
        • -10 Box: TATAAT (Pribnow box), located about 10 base pairs upstream of the transcription start site (+1).
        • -35 Box: TTGACA, located about 35 base pairs upstream of the transcription start site.
      • DNA Signature: 5' - TTGACA (N16-18) TATAAT - 3'
    • Ribosome Binding Site (RBS):
      • Shine-Dalgarno Sequence: The Shine-Dalgarno sequence is located 6-10 bases upstream of the start codon (AUG) and aligns the ribosome for translation initiation.
      • DNA Signature: 5' - AGGAGG - 3'
    • Coding Sequence (CDS):
      • Open Reading Frame (ORF): The coding region starts with the start codon (AUG, which codes for methionine) and ends with one of the stop codons (UAG, UAA, UGA).
      • DNA Signature: 5' - ATG (coding region) TAG/TAA/TGA - 3'
    • Terminator Region:
      • Rho-independent: Contains a palindromic sequence that forms a hairpin loop followed by a series of uracils in the RNA transcript (or thymine in DNA).
      • DNA Signature: 5' - GC-rich palindrome (stem-loop) followed by TTTTTT - 3'
      • Rho-dependent: Does not have a specific sequence but relies on the Rho protein to terminate transcription.
    • Operon:
      • Multiple Genes under One Promoter: Operons like the lac operon have several genes (e.g., lacZ, lacY, lacA) transcribed from a single promoter and regulated by a single operator.
      • DNA Signature: 5' - Promoter (TTGACA...TATAAT) Operator Coding Regions (ATG...TAG/TAA/TGA) - 3'

    Eukaryotic Gene Structure - DNA Signatures

    • Promoter Region:
      • TATA Box: Located about 25-30 base pairs upstream of the transcription start site. Other elements such as the CAAT box or GC-rich regions may also be present.
      • DNA Signature: 5' - TATAAAA - 3' - Optional upstream elements like the CAAT Box: 5' - GGCCAATCT - 3'
    • Exons and Introns:
      • Exons: Coding sequences that remain in the mature mRNA after splicing.
      • Introns: Non-coding sequences that are spliced out of pre-mRNA.
      • Splice Site Sequences:
        • 5' Splice Site (Donor Site): 5' - GU - 3' at the start of the intron.
        • 3' Splice Site (Acceptor Site): 5' - AG - 3' at the end of the intron.
        • Branch Point: A conserved "A" about 20-50 nucleotides upstream of the 3' splice site.
      • DNA Signature: 5' - Exon GU (Intron) AG Exon - 3'
    • 5' Untranslated Region (5' UTR):
      • DNA Signature: The 5' UTR varies in length and sequence and contains regulatory elements that influence translation efficiency.
    • Enhancers and Silencers:
      • Enhancers: Distant regulatory elements that can increase transcription.
      • Silencers: Elements that suppress gene expression.
      • DNA Signature: Enhancer and silencer sequences do not have a fixed sequence but often contain binding sites for transcription factors like NF-κB, SP1, or Oct4.
    • Polyadenylation Signal:
      • Poly-A Tail Addition: A signal in the 3' untranslated region (3' UTR) instructs the addition of a poly-A tail to the mRNA transcript.
      • DNA Signature: 5' - AAUAAA - 3'
    • 3' Untranslated Region (3' UTR):
      • DNA Signature: Often variable, the 3' UTR contains sequences that influence mRNA stability, localization, and translation.

    Comparison of DNA Signatures:

    Element Prokaryotic Signature Eukaryotic Signature
    Promoter -35 TTGACA -10 TATAAT TATAAAA (TATA Box)
    Ribosome Binding Site Shine-Dalgarno: AGGAGG No specific sequence, but Kozak sequence: ACCAUGG
    Start Codon ATG ATG
    Terminator Rho-independent: GC-rich + TTTTTT No fixed terminator, polyadenylation: AAUAAA
    Intron/Exon No introns 5' GU...AG 3'
    Poly-A Signal Not present AAUAAA

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