31 Questions
What is the primary function of the RNA-Induced Silencing Complex (RISC)?
To degrade mRNAs with complementary sequences to small RNAs
What type of exoribonuclease activity is responsible for degrading mRNAs from the 5' end to the 3' end?
5'-3' Exoribonuclease Activity
What is the primary function of decapping enzymes in mRNA degradation?
To expose the mRNA to 5'-3' exoribonucleases
What type of mRNA is degraded by the exosome?
mRNAs with poly(A) tails that are too short
What is the primary function of Nonsense-Mediated Decay (NMD)?
To prevent the synthesis of truncated proteins that could be toxic to the cell
What is the overall result of the coordinated action of these mRNA degradation mechanisms?
The regulation of mRNA degradation to ensure the quality of gene expression
In eukaryotes, what happens to the poly(A) tail of an mRNA that is destined for degradation?
It is shortened to trigger degradation.
What is the primary mechanism of RNA degradation in eukaryotes?
Exonucleolytic degradation from both directions.
What occurs to an mRNA before it is degraded in eukaryotes?
The poly(A) tail is shortened.
What is the purpose of the poly(A) tail in eukaryotes?
To increase the mRNA's stability.
What is the function of the decapping enzyme Dcp1p in yeast?
To remove the cap from the 5' end of the mRNA.
What is the primary mechanism of mRNA degradation occurring in an endonucleolytic manner?
Endonucleolytic cleavage in the nucleus followed by degradation
What is the function of the poly(U) tail in defective mRNAs?
To mark mRNAs for degradation
What is the term for the degradation of mRNAs that occurs concurrently with translation?
Co-translational degradation
What is the function of the P bodies in mRNA metabolism?
To store and regulate the translation of mRNAs
What is the term for the formation of membrane-less organelles that store and regulate mRNAs?
P bodies
What is the role of ribosomes in the regulation of mRNA translation?
To translate mRNAs into proteins in response to stimuli
What is the function of ARE (A/U rich elements) in mRNA regulation?
To attract degradation machinery to mRNAs
What is the role of Puf3,4,5p and Mpt5p proteins in mRNA regulation?
To attract degradation machinery to mRNAs
What is the function of the complex EJC (Exon Junction Complex) in mRNA regulation?
To come with mRNAs from the nucleus to the cytoplasm
What is the term for a group of genes regulated by a common set of RNA-binding proteins?
Regulon
What is the primary function of the 5'UTR region in a eukaryotic mRNA?
To regulate the stability or localization of the transcript
What is the effect of methylation of adenines in the UTR region of an mRNA?
It attracts proteins that regulate the stability of the mRNA
What is the function of the IRE (Iron Response Element) in the mRNA of ferritin and transferrin?
To regulate the stability of the mRNA
What is the effect of the binding of IRE-BP to the IRE element in the mRNA of ferritin and transferrin?
It blocks the translation of ferritin and increases the stability of transferrin
What is the result of the coordinated action of the IRE-BP and the IRE element in response to iron levels?
Decreased ferritin and increased transferrin levels
What happens to the aconitase enzyme when there is no iron?
It changes its identity and becomes a RNA-binding protein
What is the role of PABP in the life cycle of mRNA?
It stabilizes mRNA and participates in translation initiation
What is the effect of shortening the poly(A) tail of an mRNA?
It decreases the stability of the mRNA
What is the purpose of the TRAMP complex in the degradation of RNA?
To degrade faulty rRNA and other aberrant RNAs
What is the purpose of the ribophagy process?
To recycle ribosomal components
Study Notes
mRNA Degradation in Eukaryotes
RNA-Induced Silencing Complex (RISC)
- A protein complex that mediates RNA interference (RNAi) and microRNA (miRNA) pathways
- Contains an endonuclease, Argonaute (AGO), that cleaves target mRNAs
- RISC-mediated degradation is a post-transcriptional regulation mechanism
- Inhibits gene expression by degrading mRNAs with complementary sequences to small RNAs (siRNAs and miRNAs)
5'-3' Exoribonuclease Activity
- A process where exoribonucleases degrade mRNAs from the 5' end to the 3' end
- Involves the sequential removal of nucleotides from the 5' end of the mRNA
- Xrn1 is a 5'-3' exoribonuclease that degrades mRNAs in the cytoplasm
- Plays a role in mRNA quality control and degradation of aberrant mRNAs
Decapping Enzymes
- Decapping is the removal of the 7-methylguanosine (m7G) cap from the 5' end of the mRNA
- Decapping enzymes, such as Dcp2, initiate mRNA degradation by exposing the mRNA to 5'-3' exoribonucleases
- Decapping is a key step in mRNA degradation and is regulated by various cellular signals
Exosome-Mediated Degradation
- The exosome is a complex of 3'-5' exoribonucleases that degrades mRNAs from the 3' end
- Involved in the degradation of aberrant mRNAs and mRNAs with defective 3' untranslated regions (UTRs)
- The exosome is also involved in the degradation of mRNAs with poly(A) tails that are too short
Nonsense-Mediated Decay (NMD)
- A quality control mechanism that degrades mRNAs with premature stop codons
- NMD prevents the synthesis of truncated proteins that could be toxic to the cell
- Involves the recognition of aberrant mRNAs by the NMD machinery, which then targets the mRNA for degradation
These mechanisms work together to regulate mRNA degradation in eukaryotes, ensuring the quality of gene expression and preventing the accumulation of aberrant mRNAs.
Learn about the mechanisms of mRNA degradation in eukaryotes, including RNA-induced silencing complex (RISC), 5'-3' exoribonuclease activity, decapping enzymes, exosome-mediated degradation, and nonsense-mediated decay (NMD). Understand how these mechanisms work together to regulate gene expression and prevent the accumulation of aberrant mRNAs.
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