T.15 El spliceosoma

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Questions and Answers

What is the primary function of spliceosomes in pre-mRNA processing?

To transcribe DNA into pre-mRNA

To translate pre-mRNA into protein

To degrade faulty mRNA molecules

To remove introns and join exons to form mature mRNA (correct)

What is the outcome of the two-step process of splicing in spliceosomes?

Cleavage of the 5' splice site and release of the exon

Formation of a lariat structure and release of the intron (correct)

Cleavage of the 3' splice site and retention of the exon

Formation of a lariat structure and retention of the intron

How do spliceosomes regulate gene expression at the post-transcriptional level?

By translating mRNA into protein

By controlling transcription initiation

By controlling the inclusion or exclusion of exons (correct)

By degrading mRNA molecules

What is the result of alternative splicing mediated by spliceosomes?

Generation of different mRNA isoforms from a single gene Signup and view all the answers

What is the role of small nuclear RNAs (snRNAs) in spliceosome function?

To mediate interactions between pre-mRNA and spliceosomes Signup and view all the answers

What is the outcome of differential splicing mediated by spliceosomes?

Generation of different mRNA isoforms in response to environmental cues Signup and view all the answers

What is the reason for the U3 being classified as a snRNA?

It is a historical mistake Signup and view all the answers

What is the characteristic of the U7 that distinguishes it from the other U-snRNAs?

It is involved in the processing of histone mRNAs Signup and view all the answers

Why do the 7 U-snRNAs have the names they do?

They were named in the order of their discovery Signup and view all the answers

What is the role of proteins in the spliceosome?

They are essential for the structure of the spliceosome Signup and view all the answers

What is the characteristic of the U-snRNAs in the spliceosome?

They are always found in complexes with proteins Signup and view all the answers

What is the main role of U2 snRNA in the splicing process?

Recognizing the branching point in the intron Signup and view all the answers

Why do some introns have imperfect consensus sequences?

To allow for alternative splicing Signup and view all the answers

What is the role of U2AF proteins in the splicing process?

Recruiting the U2 snRNA to the splice site Signup and view all the answers

How does the spliceosome recognize the 5' and 3' ends of the intron?

Through the U1 snRNA and U2AF proteins, respectively Signup and view all the answers

What is the function of the U11, U12, and other minor snRNAs?

They participate in the minor spliceosome pathway Signup and view all the answers

What is the unique feature of the 2’OH in the special conformation of the spliceosome?

It has a different location than the rest of the nucleotides Signup and view all the answers

What is the approximate size of the spliceosome machinery?

12.3 MDa Signup and view all the answers

Which snRNA is responsible for recognizing the 5' splice site?

U1 Signup and view all the answers

What is the role of U6 in the spliceosome?

It forms hybrids with U4 and U2 Signup and view all the answers

What is the outcome of the interaction between U2 and U6 in the spliceosome?

It promotes the attack of the 2'OH of the adenine Signup and view all the answers

What is the location where the spliceosome 'waits' for the RNA polymerase to start transcribing introns?

Cola CTD Signup and view all the answers

What is the fate of introns that have been spliced out of the primary transcript?

They are degraded immediately Signup and view all the answers

What is the function of the corpúsculos de Cajal (Cajal bodies) in the nucleus?

They are storage sites for inactive spliceosomes Signup and view all the answers

What is the significance of the finding that introns are mostly found in the nucleus?

It suggests that splicing is a co-transcriptional process Signup and view all the answers

What is the function of the complex E in the formation of the spliceosome?

To produce the folding of the inner part of the intron Signup and view all the answers

What is the purpose of marking introns with different fluorophores in the experiment described?

To identify the location of introns in the cell Signup and view all the answers

What is the role of U6 in the formation of the complex B1?

It pairs with U2 to form the complex B1 Signup and view all the answers

What happens to U1 during the formation of the complex B2?

It is released from the complex Signup and view all the answers

What is the function of the complex C1?

To catalyze the splicing reaction Signup and view all the answers

What is the result of the interaction between U6 and U2 during the formation of the complex C1?

U2 and U6 form a complex Signup and view all the answers

Study Notes

Spliceosomes

Splicing Mechanisms

Intron removal: Spliceosomes remove introns (non-coding regions) from pre-mRNA, joining exons (coding regions) to form mature mRNA.
Two-step process:
1. Branch point formation: A lariat structure is formed between the branch point and the 5' splice site.
2. Splice site cleavage: The 5' splice site is cleaved, and the intron is released.

RNA Processing

Pre-mRNA splicing: Spliceosomes play a crucial role in pre-mRNA splicing, which occurs in the nucleus.
Alternative splicing: Spliceosomes can generate different mRNA isoforms from a single gene by selecting different splice sites.
RNA-RNA interactions: Spliceosomes mediate interactions between pre-mRNA and small nuclear RNAs (snRNAs) to facilitate splicing.

Post-transcriptional Regulation

Regulation of gene expression: Spliceosomes can regulate gene expression by controlling the inclusion or exclusion of exons, affecting protein function.
Tissue-specific splicing: Spliceosomes can generate tissue-specific mRNA isoforms, contributing to cellular diversity.

Gene Expression

Spliceosome-mediated gene regulation: Spliceosomes can regulate gene expression by controlling the production of functional mRNA.
Differential splicing: Spliceosomes can generate different mRNA isoforms in response to environmental cues or developmental signals.

Spliceosome Structure

Small nuclear ribonucleoproteins (snRNPs): Spliceosomes consist of snRNPs, which are complexes of snRNAs and proteins.
Core components:
- U1 snRNP: recognizes the 5' splice site.
- U2 snRNP: recognizes the branch point.
- U4/U6 snRNP: catalyzes the splicing reaction.
- U5 snRNP: interacts with the 5' and 3' splice sites.
Dynamic structure: The spliceosome undergoes significant structural rearrangements during the splicing process.

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Description

This quiz covers the mechanisms of spliceosomes in RNA processing, including intron removal, alternative splicing, and post-transcriptional regulation. Learn about the structure and function of spliceosomes and their role in gene expression.