mRNA Degradation Mechanisms
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Questions and Answers

Which enzyme class recognizes and binds to the 3' end of mRNA?

  • Deadenylation complex
  • Decapping enzymes
  • Exoribonucleases (correct)
  • RNA-induced silencing complex

    • What is the function of decapping enzymes in mRNA degradation?

  • Hydrolyze the phosphodiester bonds, releasing nucleotides
  • Recruit the RNA-induced silencing complex
  • Recognize and bind to the poly(A) tail
  • Remove the 7-methylguanosine (m7G) cap from the 5' end of mRNA (correct)

    • What is the primary function of Nonsense-Mediated Decay (NMD)?

  • Recognition of the m7G cap from the 5' end of mRNA
  • Surveillance mechanism to degrade mRNAs with premature stop codons (correct)
  • Removal of the poly(A) tail from the 3' end of mRNA
  • MicroRNA-mediated degradation of target mRNAs

    • How do microRNAs (miRNAs) induce degradation of target mRNAs?

    <p>By recruiting the RNA-induced silencing complex (RISC) and Argonaute protein-mediated degradation</p> Signup and view all the answers

    What is the role of deadenylation in mRNA degradation?

    <p>Removal of the poly(A) tail, making the mRNA susceptible to degradation</p> Signup and view all the answers

    Which complex is responsible for deadenylation?

    <p>CCR4-NOT complex</p> Signup and view all the answers

    What is the main reason for the difference in stability between mRNA in prokaryotes and eukaryotes?

    <p>The rate of cell division and replication</p> Signup and view all the answers

    What is the purpose of having different mRNA stabilities in cells?

    <p>To allow for rapid adaptation to changes in the environment</p> Signup and view all the answers

    Why do mRNAs in human cells have longer lifetimes compared to E. coli?

    <p>Because human cells have a longer lifespan</p> Signup and view all the answers

    What happens to mRNA molecules when a cell divides?

    <p>They are inherited by the daughter cells</p> Signup and view all the answers

    Why are some mRNAs more unstable than others?

    <p>Because they are involved in response to stress and hormones</p> Signup and view all the answers

    What is the relationship between mRNA stability and the lifespan of a cell?

    <p>mRNA stability increases with increasing cell lifespan</p> Signup and view all the answers

    Why do cells have different mRNA stability for different genes?

    <p>To allow for rapid adaptation to changes in the environment</p> Signup and view all the answers

    What is the effect of rapid mRNA degradation on cellular energy expenditure?

    <p>It increases energy expenditure due to rapid mRNA synthesis</p> Signup and view all the answers

    Why do some genes require more rapid mRNA degradation than others?

    <p>Because they are involved in response to stress and hormones</p> Signup and view all the answers

    Why is RNA with a non-coding function relatively more stable?

    <p>Because its function is static and serves all cells regardless of environmental conditions</p> Signup and view all the answers

    What is the main reason for the degradation of RNA molecules?

    <p>To allow for changes in quantity necessary for varying cellular responses</p> Signup and view all the answers

    What is the main difference between the stability of DNA and RNA?

    <p>DNA can be copied, allowing it to persist longer</p> Signup and view all the answers

    Why are defective RNA molecules eliminated?

    <p>To eliminate non-functional RNA molecules</p> Signup and view all the answers

    What is the main advantage of RNA degradation?

    <p>It allows for changes in quantity necessary for varying cellular responses</p> Signup and view all the answers

    What is the relationship between RNA stability and cellular growth?

    <p>RNA stability decreases with cellular growth</p> Signup and view all the answers

    Why are non-coding RNA molecules more stable than messenger RNA molecules?

    <p>Because they adopt unique 3D structures that stabilize them</p> Signup and view all the answers

    What is the main consequence of not degrading RNA molecules?

    <p>Accumulation of defective RNA molecules</p> Signup and view all the answers

    What is the consequence of the balance between the rates of synthesis and degradation of RNA?

    <p>The RNA population reaches a steady state</p> Signup and view all the answers

    What is the purpose of degrading incorrect RNA molecules?

    <p>To eliminate faulty RNA molecules</p> Signup and view all the answers

    What determines the stability of an RNA molecule?

    <p>The rate of degradation</p> Signup and view all the answers

    What is the relationship between the rate of transcription and the rate of degradation?

    <p>They are directly proportional</p> Signup and view all the answers

    What is the purpose of the 'model pool'?

    <p>To describe the relationship between transcription and degradation</p> Signup and view all the answers

    What is the consequence of a low degradation rate for an RNA molecule?

    <p>The RNA molecule is more stable</p> Signup and view all the answers

    What is the role of the RNA polymerase in transcription?

    <p>To elongate the RNA chain</p> Signup and view all the answers

    What is the significance of the half-life of an RNA molecule?

    <p>It is the time required for the RNA molecule to be reduced to half its original amount</p> Signup and view all the answers

    Study Notes

    mRNA Degradation

    Exoribonucleases

    • Exoribonucleases are a class of enzymes that degrade mRNA from the 3' end
    • Examples: RNase II and RNase R
    • Mechanism:
      • Recognize and bind to the 3' end of mRNA
      • Hydrolyze the phosphodiester bonds, releasing nucleotides
      • Processive degradation: continue to degrade the mRNA until it is completely broken down

    Decapping

    • Decapping is the removal of the 7-methylguanosine (m7G) cap from the 5' end of mRNA
    • Decapping enzymes: Dcp1 and Dcp2
    • Mechanism:
      • Recognize and bind to the m7G cap
      • Hydrolyze the cap, removing it from the mRNA
      • Exoribonucleases can then access the 5' end and degrade the mRNA

    Nonsense-Mediated Decay (NMD)

    • NMD is a surveillance mechanism that degrades mRNAs with premature stop codons
    • Recognizes and degrades aberrant mRNAs to prevent the synthesis of truncated proteins
    • Mechanism:
      • Recognition of the premature stop codon by the ribosome
      • Recruitment of the NMD machinery, including UPF1 and UPF2
      • Degradation of the mRNA by decapping and exoribonucleolytic degradation

    MicroRNA-mediated Degradation

    • MicroRNAs (miRNAs) are small RNAs that bind to target mRNAs and induce degradation
    • Mechanism:
      • miRNA binding to the 3' UTR of the target mRNA
      • Recruitment of the RNA-induced silencing complex (RISC)
      • Argonaute protein-mediated degradation of the mRNA
      • Deadenylation and exoribonucleolytic degradation of the mRNA

    Deadenylation

    • Deadenylation is the removal of the poly(A) tail from the 3' end of mRNA
    • Deadenylation is a key step in mRNA degradation
    • Mechanism:
      • Recognition of the poly(A) tail by deadenylases (e.g., CCR4-NOT complex)
      • Shortening of the poly(A) tail, making the mRNA susceptible to degradation by exoribonucleases

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    Description

    This quiz covers the different mechanisms of mRNA degradation, including exoribonucleases, decapping, nonsense-mediated decay, microRNA-mediated degradation, and deadenylation. Learn about the enzymes and complexes involved in each process and how they contribute to mRNA degradation.

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