mRNA Processing Part 1
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Questions and Answers

What are the main modifications that occur during eukaryotic mRNA processing?

Eukaryotic mRNA processing involves capping, splicing of exons, and polyadenylation at the 3' end.

Explain the role of the 5' cap in mRNA processing.

The 5' cap stabilizes the mRNA transcript and promotes efficient translation.

What is the function of the poly-A tail in mRNA?

The poly-A tail stabilizes the mRNA transcript and facilitates its translation.

What distinguishes prokaryotic mRNA processing from eukaryotic mRNA processing?

<p>Prokaryotic mRNA does not undergo additional processing, as it is transcribed in a 'ready to read' state.</p> Signup and view all the answers

Describe the importance of splicing in mRNA processing.

<p>Splicing is crucial for removing introns and linking exons, ensuring that the coding sequence is continuous.</p> Signup and view all the answers

What role do ribonucleases play in mRNA stability?

<p>Ribonucleases degrade RNA from the 5' or 3' ends and can also target internal sequences, affecting mRNA stability.</p> Signup and view all the answers

List the order of mRNA processing events.

<p>The order is: capping, splicing (during transcription), termination/polyadenylation, and splicing (after termination).</p> Signup and view all the answers

Why is mRNA inherently unstable?

<p>mRNA is inherently unstable due to its ribose sugar structure, which makes it more prone to breakage.</p> Signup and view all the answers

What specific methylation occurs in yeast's 5' cap structure?

<p>Yeast methylates the position 7 of the GTP, known as 7-m-G-cap.</p> Signup and view all the answers

In vertebrates, what additional methylation occurs at the 5' cap beyond cap–1?

<p>Vertebrates also methylate the 2 carbon of the +2 nucleotide, known as cap-2.</p> Signup and view all the answers

List two functions of the cap-binding complex in mRNA processing.

<p>The cap-binding complex stabilizes mRNA and recruits the spliceosome.</p> Signup and view all the answers

Why is the capping of mRNA crucial for viral RNA recognition?

<p>Capping prevents viral RNA from being recognized as self, which triggers an innate interferon response.</p> Signup and view all the answers

What role does the 3' Poly–A-tail play in eukaryotic mRNA termination?

<p>The 3' Poly–A-tail is involved in the stability and eventual termination of transcription in eukaryotes.</p> Signup and view all the answers

What mechanism does Rho-dependent termination utilize to remove mRNA from RNA polymerase?

<p>The Rho-dependent mechanism pulls the mRNA from RNA polymerase.</p> Signup and view all the answers

In eukaryotes, what happens to mRNA during transcription termination?

<p>The mRNA is cleaved from the transcript.</p> Signup and view all the answers

How does the Xrn2 exonuclease contribute to the termination process in eukaryotes?

<p>Xrn2 travels along the RNA, degrading it until it reaches RNA polymerase II, causing dissociation.</p> Signup and view all the answers

What roles do CstF and CPSF play during transcription termination?

<p>CstF and CPSF are involved in transcription termination and polya-denylation of the 3' end of mRNA.</p> Signup and view all the answers

What is the significance of the poly(A) signal and poly(A) site in DNA?

<p>The poly(A) signal recruits proteins for mRNA tailing, and the poly(A) site marks where adenylation begins.</p> Signup and view all the answers

What effect does the state of the pol II CTD have on transcription termination?

<p>It prevents early termination in the event of mutations near the poly(A) site or signal.</p> Signup and view all the answers

Which region does CPSF bind to during the termination process?

<p>CPSF binds to the AAUAAA poly-A signal.</p> Signup and view all the answers

What role does PAP (poly-A polymerase) play in mRNA processing?

<p>PAP adds adenine residues to the 3' end of mRNA without needing a template.</p> Signup and view all the answers

What process gradually decreases the levels of pre-mRNA and mature RNA over time?

<p>RNA degradation occurs gradually over time, leading to decreased levels of pre-mRNA and mature RNA.</p> Signup and view all the answers

How does instantaneous inhibition affect pre-mRNA levels?

<p>Instantaneous inhibition causes pre-mRNA levels to drop quickly as they are processed into mature RNA.</p> Signup and view all the answers

What is the significance of mRNA stability in eukaryotic cells?

<p>Increased mRNA stability allows one transcript to yield more rounds of translated proteins.</p> Signup and view all the answers

Compare the mRNA half-life between E. coli and H. sapiens.

<p>E. coli mRNAs are degraded in about 3-5 minutes, while H. sapiens mRNA can last over 10 hours.</p> Signup and view all the answers

What role does the 5' cap play in mRNA?

<p>The 5' cap protects mRNA from degradation by exonucleases and aids in translation.</p> Signup and view all the answers

When are capping enzymes recruited during mRNA synthesis?

<p>Capping enzymes are recruited when the transcript is about 20-30 bases long.</p> Signup and view all the answers

What modification is made to the inverted guanine during capping?

<p>The inverted guanine is methylated at position 7 by guanine-7-methyl transferase.</p> Signup and view all the answers

How does RNA's ribose structure contribute to its instability?

<p>RNA is unstable due to the presence of an extra -OH group in its ribose sugar.</p> Signup and view all the answers

Describe the bond formed between the 5' cap and the mRNA.

<p>A 5' to 5' bond is formed between the inverted GTP and the 5' end of the growing mRNA.</p> Signup and view all the answers

What happens to the two 2' ends of the first two nucleotides during RNA capping?

<p>Methyl transferase can methylate the 2' -OH of the first two nucleotides.</p> Signup and view all the answers

What role does poly-A polymerase (PAP) play in polyadenylation?

<p>PAP adds adenine nucleotides to the 3’ end of the mRNA after it is cleaved, and its activity requires binding of poly-A binding protein (PAB).</p> Signup and view all the answers

How does the presence of a cap and tail affect the half-life of mRNA?

<p>Having a cap and tail significantly extends the half-life of mRNA, allowing it to persist longer in the cell.</p> Signup and view all the answers

Describe how mRNA stability is influenced by its modifications.

<p>Modified mRNA with caps and tails is more stable, translating faster than unmodified forms due to enhanced protection against degradation.</p> Signup and view all the answers

What effect does the absence of either a cap or tail have on mRNA translation?

<p>The absence of either a cap or tail leads to a significant reduction in translation efficiency, with translation becoming notably cap-dependent.</p> Signup and view all the answers

Explain the interaction between the 5’ cap and the 3’ poly-A tail.

<p>The 5’ cap interacts with eukaryotic intrinsic factors, which associate with the 3’ poly-A tail via PABP, forming a closed-loop structure.</p> Signup and view all the answers

What are the consequences of excess caps or tails on mRNA translation?

<p>Excess caps or tails destabilize the mRNA by blocking the recycling of ribosomes, thus reducing the efficiency of translation.</p> Signup and view all the answers

What is the importance of poly-A binding protein (PAB) during polyadenylation?

<p>PAB is crucial as it binds to the added adenine residues, stimulating further polyadenylation by PAP.</p> Signup and view all the answers

How does cleavage of pre-mRNA relate to the addition of the poly-A tail?

<p>Cleavage of pre-mRNA occurs about 35 bases past the AAUAAA signal, which initiates the polyadenylation process.</p> Signup and view all the answers

Study Notes

mRNA Processing Part 1

  • Prokaryotic mRNA transcription and translation occur concurrently in the nucleoid. This mRNA does not require further processing.
  • Eukaryotic mRNA necessitates processing to create a mature transcript.
  • Pre-mRNA is transcribed in the nucleus.
  • Modifications occur at the 5' and 3' ends.
  • Introns are removed, and exons are joined during mRNA splicing.
  • mRNA is exported from the nucleus to the cytoplasm.
  • Translation regulation involves activating desired messages and suppressing undesired ones (e.g., delayed translation).
  • Stability and degradation of mRNA are controlled.

Overview of RNA Processing

  • Mature mRNA includes:
    • A 5' cap and 5' UTR (untranslated region), which stabilizes the transcript and enhances translation efficiency.
    • Start codon, open reading frame (ORF), and stop codon.
    • 3' UTR and poly-A tail, increasing transcript stability and enhancing translation efficiency.
  • Processing events:
    • Capping
    • Splicing (during transcription)
    • Termination/Polyadenylation
    • Splicing (after termination)

mRNA Stability

  • RNA structure, especially the ribose sugar's extra hydroxyl group (-OH), makes mRNA inherently unstable and prone to degradation.
  • Ribonucleases can target 5' and 3' ends or internal sequences or structures (endonucleases).
  • Degradation of RNA occurs for recycling.
  • Drugs or heat shock mutations can terminate transcription.

mRNA Half-Life

  • E. coli mRNA degrades rapidly (3-5 minutes).
  • S. cerevisiae mRNA degrades relatively slower (20-30 minutes).
  • Human mRNA degrades comparatively slowly (10+ hours).
  • Intact mRNA is more stable, translating into more protein.
  • mRNA half-life varies across organisms.

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BMSC 320 Lecture 22: mRNA Processing PDF

Description

This quiz covers the essential concepts of mRNA processing, focusing on the differences between prokaryotic and eukaryotic systems. You will explore the stages of transcription, modifications, splicing, and the significance of various regions in mature mRNA. Test your understanding of how these processes contribute to gene expression regulation.

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