mRNA Degradation Mechanisms

Questions and Answers

What triggers the 3’-to-5’ degradation of mRNA due to a critical threshold?

Loss of poly-A binding proteins (correct)

Excessive translation initiation

Increased methyl cap stability

Shortening of the mRNA sequence

Which of the following statements correctly describes the role of P bodies in mRNA decay?

P bodies regulate cellular signaling.

P bodies are exclusively for storing mRNA.

P bodies are cytoplasmic structures where RNA decay occurs. (correct)

P bodies concentrate translation initiation factors.

How do AUUUA elements (AREs) affect mRNA stability?

They increase the rate of deadenylation. (correct)

They promote the synthesis of new mRNA.

They inhibit protein binding to mRNA.

They stabilize mRNA by enhancing translation.

What is the relationship between translational initiation efficiency and mRNA degradation?

Changes in translation efficiency affect mRNA degradation inversely. Signup and view all the answers

What is the length of the Open Reading Frame (ORF) in the mature mRNA if it encodes a 50 amino acid protein?

150 nucleotides Signup and view all the answers

What external factors can regulate RNA-binding proteins that stabilize mRNA?

Extracellular signals like growth factors Signup and view all the answers

What must occur before the rapid degradation of mRNA after its poly-A tail is removed?

Methyl cap removal at the 5’ end Signup and view all the answers

Which of the following statements best describes the role of the cap-binding protein (CBC) in mRNA processing?

It marks successful modifications for nuclear export. Signup and view all the answers

What is the primary purpose of translation-dependent mRNA surveillance mechanisms?

To detect and degrade aberrant transcripts. Signup and view all the answers

Which of the following processes can occur simultaneously on the same mRNA molecule?

Decapping and deadenylation Signup and view all the answers

What is a likely consequence of competitive binding of proteins to mRNA?

Enhanced mRNA degradation Signup and view all the answers

Which of these is a component required for the nucleus export of processed mRNA?

Poly A binding protein (PABP) Signup and view all the answers

What components constitute the three main sections of mature mRNA?

5’ UTR, ORF, 3’ UTR Signup and view all the answers

What signifies that an mRNA transcript has undergone proper processing required for export from the nucleus?

The presence of a methyl cap and poly A tail Signup and view all the answers

In the context of mRNA degradation pathways, what does nonsense-mediated decay (NMD) specifically target?

Transcripts with premature termination codons (PTCs) Signup and view all the answers

During mRNA translation initiation, what do eukaryotic initiation factors (eIFs) recognize?

Proteins bound to the 5’ and 3’ ends of mRNA Signup and view all the answers

What is the primary consequence of longer mRNA half-life for protein translation?

Increased protein synthesis Signup and view all the answers

Which type of mRNA typically has very short half-lives?

mRNAs encoding growth factors Signup and view all the answers

How does the length of the poly-A tail relate to mRNA stability?

Longer tail corresponds with longer half-life Signup and view all the answers

Which sequence in the 3' UTR is known to promote removal of the poly-A tail?

AU-rich sequences Signup and view all the answers

What is the first step in the predominant pathway of normal mRNA degradation?

Deadenylation of the mRNA Signup and view all the answers

What role do specific regulators play in mRNA half-life?

They protect mRNA from degradation Signup and view all the answers

What is the significance of iron scarcity in the regulation of transferrin receptor mRNA?

It protects transferrin receptor RNA from degradation Signup and view all the answers

What is one possible outcome of mRNA degradation pathways on gene expression?

Alteration of gene expression regulation Signup and view all the answers

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.