T.15 Procesamiento de mRNAs: intrones GU-AG
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Questions and Answers

What is the primary function of the spliceosome?

  • To modify nucleotides to change the amino acid sequence
  • To add a poly(A) tail to the 3' end of pre-mRNA
  • To remove introns and join exons in pre-mRNA (correct)
  • To transcribe DNA into pre-mRNA

    • What is the function of the U1 snRNP in the spliceosome?

  • To catalyze transesterification reactions
  • To bind to the AG motif at the 3' splice site
  • To add a 7-methylguanosine cap to the 5' end of pre-mRNA
  • To bind to the GU motif at the 5' splice site (correct)

    • What is the purpose of capping in mRNA maturation?

  • To remove introns and join exons in pre-mRNA
  • To modify nucleotides to change the amino acid sequence
  • To protect the 5' end of pre-mRNA from degradation (correct)
  • To add a poly(A) tail to the 3' end of pre-mRNA

    • What is the outcome of alternative splicing?

    <p>The production of multiple isoforms of mRNA from a single gene</p> Signup and view all the answers

    What defines the exon-intron boundary?

    <p>The GU-AG motif</p> Signup and view all the answers

    What is the outcome of intron removal and exon joining?

    <p>The production of a mature mRNA molecule</p> Signup and view all the answers

    What is a common characteristic shared by tRNA introns?

    <p>Similar size and tertiary structure</p> Signup and view all the answers

    What is a key difference between introns in mRNA and tRNA?

    <p>mRNA introns have variable lengths, unlike tRNA introns</p> Signup and view all the answers

    What is the function of the conserved sequences at the 5' and 3' ends of introns?

    <p>To recognize the intron for processing</p> Signup and view all the answers

    What is a characteristic of the consensus sequence in introns?

    <p>It is highly conserved, but not identical</p> Signup and view all the answers

    What is the typical sequence found at the 5' end of introns?

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

    What is the typical sequence found at the 3' end of introns?

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

    What is the significance of the branching point in introns?

    <p>It is the site of a highly conserved adenine</p> Signup and view all the answers

    What is the significance of the G nucleotide at the exon-intron boundary?

    <p>It is a conserved sequence at the exon-intron boundary</p> Signup and view all the answers

    What is the position of the branching point in the intron?

    <p>Very close to the 3' end of the intron</p> Signup and view all the answers

    What is the significance of the GU and AG consensus sequences in introns?

    <p>They are highly conserved and mark the intron for processing</p> Signup and view all the answers

    What is the significance of the variable length of the central part of the RNA?

    <p>It allows the RNA to fold in a specific way to bring distant parts together.</p> Signup and view all the answers

    What is the role of the 2'OH group in the reaction of intron excision?

    <p>It performs a nucleophilic attack on the phosphodiester bond between two guanines.</p> Signup and view all the answers

    Why does the reaction of intron excision occur only in RNA and not in DNA?

    <p>Because RNA has a 2'OH group that can perform a nucleophilic attack.</p> Signup and view all the answers

    What is the consequence of the second nucleophilic attack in the intron excision reaction?

    <p>The release of the intron in a lariat form.</p> Signup and view all the answers

    What is the role of the U-snRNAs in the intron excision reaction?

    <p>They form a complex with the intron and position the adenine correctly.</p> Signup and view all the answers

    What is the significance of the consensus sequence in the RNA?

    <p>It is recognized by RNAs and proteins that play a role in the splicing reaction.</p> Signup and view all the answers

    What is the structure formed by the adenine and the intron during the reaction?

    <p>A lariat structure.</p> Signup and view all the answers

    What is the difference between the first and second nucleophilic attacks in the intron excision reaction?

    <p>The first attack is performed by the 2'OH group, while the second is performed by a 3'OH group.</p> Signup and view all the answers

    What is the significance of the autocatalytic intron in mitochondria?

    <p>It does not require any external factors for function.</p> Signup and view all the answers

    What is the outcome of the intron excision reaction?

    <p>The release of the intron in a lariat form.</p> Signup and view all the answers

    Study Notes

    Spliceosome Function

    • The spliceosome is a large ribonucleoprotein complex responsible for removing introns and joining exons in pre-mRNA
    • Composed of 5 snRNPs (small nuclear ribonucleoproteins) and over 100 proteins
    • Catalyzes two transesterification reactions to form a lariat structure and release the intron
    • Leaves a continuous mature mRNA molecule

    GU-AG Recognition

    • The spliceosome recognizes the GU-AG motif at the intron-exon boundaries
    • GU at the 5' splice site and AG at the 3' splice site
    • The U1 snRNP binds to the GU motif, and the U2 snRNP binds to the AG motif
    • This recognition is crucial for the spliceosome to accurately remove introns and join exons

    mRNA Maturation

    • After transcription, the pre-mRNA undergoes several processing steps to mature into functional mRNA
    • These steps include:
      • Splicing: removal of introns and joining of exons
      • Capping: addition of a 7-methylguanosine cap to the 5' end
      • Polyadenylation: addition of a poly(A) tail to the 3' end
      • Editing: modification of nucleotides to change the amino acid sequence

    Alternative Splicing

    • The process by which different exons are included or excluded to produce multiple isoforms of mRNA from a single gene
    • Allows for the generation of different protein isoforms with varying functions
    • Regulated by various factors, including:
      • Splicing factors
      • Hormones
      • Cellular signals
      • Tissue-specific expression

    Intron-Exon Definition

    • Introns: non-coding regions of DNA that are removed during splicing
    • Exons: coding regions of DNA that are joined together to form the mature mRNA
    • The exon-intron boundary is defined by the GU-AG motif
    • The spliceosome recognizes this motif to accurately remove introns and join exons

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    Description

    This quiz covers the function of the spliceosome in removing introns and joining exons in pre-mRNA, including GU-AG recognition, mRNA maturation, alternative splicing, and exon-intron definition.

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