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Questions and Answers
What triggers the 3’-to-5’ degradation of mRNA due to a critical threshold?
What triggers the 3’-to-5’ degradation of mRNA due to a critical threshold?
Which of the following statements correctly describes the role of P bodies in mRNA decay?
Which of the following statements correctly describes the role of P bodies in mRNA decay?
How do AUUUA elements (AREs) affect mRNA stability?
How do AUUUA elements (AREs) affect mRNA stability?
What is the relationship between translational initiation efficiency and mRNA degradation?
What is the relationship between translational initiation efficiency and mRNA degradation?
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What is the length of the Open Reading Frame (ORF) in the mature mRNA if it encodes a 50 amino acid protein?
What is the length of the Open Reading Frame (ORF) in the mature mRNA if it encodes a 50 amino acid protein?
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What external factors can regulate RNA-binding proteins that stabilize mRNA?
What external factors can regulate RNA-binding proteins that stabilize mRNA?
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What must occur before the rapid degradation of mRNA after its poly-A tail is removed?
What must occur before the rapid degradation of mRNA after its poly-A tail is removed?
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Which of the following statements best describes the role of the cap-binding protein (CBC) in mRNA processing?
Which of the following statements best describes the role of the cap-binding protein (CBC) in mRNA processing?
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What is the primary purpose of translation-dependent mRNA surveillance mechanisms?
What is the primary purpose of translation-dependent mRNA surveillance mechanisms?
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Which of the following processes can occur simultaneously on the same mRNA molecule?
Which of the following processes can occur simultaneously on the same mRNA molecule?
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What is a likely consequence of competitive binding of proteins to mRNA?
What is a likely consequence of competitive binding of proteins to mRNA?
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Which of these is a component required for the nucleus export of processed mRNA?
Which of these is a component required for the nucleus export of processed mRNA?
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What components constitute the three main sections of mature mRNA?
What components constitute the three main sections of mature mRNA?
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What signifies that an mRNA transcript has undergone proper processing required for export from the nucleus?
What signifies that an mRNA transcript has undergone proper processing required for export from the nucleus?
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In the context of mRNA degradation pathways, what does nonsense-mediated decay (NMD) specifically target?
In the context of mRNA degradation pathways, what does nonsense-mediated decay (NMD) specifically target?
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During mRNA translation initiation, what do eukaryotic initiation factors (eIFs) recognize?
During mRNA translation initiation, what do eukaryotic initiation factors (eIFs) recognize?
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What is the primary consequence of longer mRNA half-life for protein translation?
What is the primary consequence of longer mRNA half-life for protein translation?
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Which type of mRNA typically has very short half-lives?
Which type of mRNA typically has very short half-lives?
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How does the length of the poly-A tail relate to mRNA stability?
How does the length of the poly-A tail relate to mRNA stability?
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Which sequence in the 3' UTR is known to promote removal of the poly-A tail?
Which sequence in the 3' UTR is known to promote removal of the poly-A tail?
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What is the first step in the predominant pathway of normal mRNA degradation?
What is the first step in the predominant pathway of normal mRNA degradation?
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What role do specific regulators play in mRNA half-life?
What role do specific regulators play in mRNA half-life?
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What is the significance of iron scarcity in the regulation of transferrin receptor mRNA?
What is the significance of iron scarcity in the regulation of transferrin receptor mRNA?
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What is one possible outcome of mRNA degradation pathways on gene expression?
What is one possible outcome of mRNA degradation pathways on gene expression?
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Study Notes
mRNA Decay and Degradation Processes
- A critical poly-A tail length leads to 3’-to-5’ degradation, possibly initiated by loss of poly-A binding proteins.
- Removal of the 5’ methyl cap can also cause rapid mRNA degradation.
- P bodies are cytoplasmic structures where RNA decay occurs, concentrating enzymes for 5’ to 3’ degradation pathways.
- Degradation and translation initiation compete; efficiency in one usually inversely affects the other.
Regulation of mRNA Stability
- AU-rich elements (AREs) in the 3’ UTR are recognized by proteins that increase deadenylation rates.
- Other RNA-binding proteins can stabilize mRNA when competing for binding, regulated by external signals (growth factors, hormones).
Structure of Mature mRNA
- Mature mRNA consists of three sections:
- 5’ UTR with a methyl cap.
- Open Reading Frame (ORF) framed by AUG start codon and stop codons (UAA, UAG, UGA).
- 3’ UTR featuring a poly-A tail.
- For a gene encoding a 50 amino acid protein:
- 5’ UTR = 50 nucleotides,
- ORF = 150 nucleotides (50 amino acids).
- 3’ UTR = 250 nucleotides.
- Total mature mRNA length = 450 nucleotides.
mRNA Export Requirements
- Only properly processed mRNAs with correct capping, splicing, and poly-A tail are exported to the cytosol.
- Proteins involved in successful mRNA modifications:
- Cap-binding protein (CBC).
- Poly A binding protein (PABP).
- Exon-junction complex (EJC).
- Eukaryotic initiation factors (eIFs) recognize bound proteins at 5’ and 3’ ends during translation initiation.
Translation-Dependent Surveillance Mechanisms
- Cells possess mechanisms for error detection in mRNA to prevent toxic protein products.
- Nonsense-mediated decay (NMD) specifically targets transcripts with premature termination codons (PTCs).
Control of mRNA Stability
- Longer mRNA half-lives correlate with greater protein translation capacity.
- "Housekeeping" genes often exhibit long half-lives due to constant need for basic cellular functions.
- Many mRNAs have shorter half-lives, particularly those coding for quickly variable proteins (growth factors, regulatory proteins).
- mRNA degradation rates can be regulated based on 3’ UTR sequences, affecting half-lives under different conditions.
mRNA Stability and Decay Mechanisms
- Gene expression can be influenced by mRNA half-life regulation, with decay rates being a significant factor.
- The length of the poly-A tail directly affects mRNA half-life; longer tails generally yield longer half-lives.
- AU-rich sequences in the 3’ UTR trigger poly-A tail removal.
- Specific regulators modulate mRNA half-life, as seen with transferrin receptor mRNA protection during iron scarcity.
- Dominant mRNA degradation pathway starts with gradual deadenylation, leading to either decapping and 5′→3′ decay or 3′→5′ decay.
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Description
Explore the critical factors involved in mRNA degradation, including the role of poly-A tail length and the implications of removing the 5’ methyl cap. This quiz covers the biochemical pathways and enzymes concentrated in P bodies pivotal in these processes.
