BLOCK 3: MBG: (3.6) RNA Processing & The Spliceosome

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Questions and Answers

What role does SNRNP play in the splicing process?

It eliminates all RNA sequences.

It provides the nucleotide sequences.

It synthesizes new RNA sequences.

It identifies splice sites. (correct)

Which of the following statements about SNRNA and SNRNP is true?

SNRNP has no role in splicing.

SNRNA is sufficient for splicing without protein.

SNRNP is only made from proteins.

SNRNA is responsible for sequence recognition. (correct)

What happens to introns after splicing?

They are incorporated into new proteins.

They are processed and eliminated. (correct)

They are transformed into exons.

They remain in the RNA sequence.

Why is the lariat structure formed during splicing important?

It serves as a marker for recognition. Signup and view all the answers

What role do SNRNAs play in the processing of mRNA?

They locate the splice sites in mRNA. Signup and view all the answers

How can the activity of nucleases be controlled in RNA processing?

Through the regulated expression of nucleases. Signup and view all the answers

Why is the presence of a template important for telomerase activity?

It provides a guide for elongating telomeres. Signup and view all the answers

What is a unique aspect of SNRNA processing in eukaryotic cells?

It involves both export and reimport of SNRNAs. Signup and view all the answers

Which elements provide indicators for RNA degradation?

Positive and negative labels. Signup and view all the answers

What is the significance of mRNA capping in RNA processing?

It enhances stability and recognition during translation. Signup and view all the answers

Which type of RNA is primarily involved in the formation of the spliceosome?

Small nuclear RNA (SNRNA) Signup and view all the answers

What does the term 'polyadenylation' refer to in mRNA processing?

The addition of a poly-A tail to the 3' end of mRNA. Signup and view all the answers

Which spliceosomal components are involved in the recognition step?

U1, U2, and U5. Signup and view all the answers

Which function does the spliceosome NOT contribute to in RNA processing?

Enhancing the stability of mRNA. Signup and view all the answers

How does SNRNA contribute to the regulation of RNA processing?

By determining splice sites based on their sequence. Signup and view all the answers

What do SNRNPs represent in the context of SNRNAs?

A complex of SNRNAs and proteins. Signup and view all the answers

What is the function of distal sequence elements (DSEs) in SNRNA processing?

To enhance transcription by improving RNA polymerase binding Signup and view all the answers

How do SNRNA and mRNA processing differ regarding the need for prior mRNA synthesis?

SNRNAs can be produced independently of prior mRNA synthesis Signup and view all the answers

What role do proximal sequence elements (PSEs) play in RNA processing?

They enhance the initiation of transcription Signup and view all the answers

In the context of gene regulation, what is a distinguishing feature of SNRNAs compared to mRNAs?

SNRNAs can be transcribed without prior mRNA synthesis Signup and view all the answers

What potential outcome occurs if an anti-termination factor is added during transcription?

Transcription is maintained, producing SNRNAs Signup and view all the answers

What is the significance of the relationship between SNRNA production and mRNA processing?

SNRNAs may assist in the processing of mRNAs despite not being preceded by them Signup and view all the answers

How do enhancer sequences contribute to gene regulation?

They increase RNA polymerase affinity for the promoter Signup and view all the answers

What is an important aspect of gene activity regarding SNRNA and mRNA?

Genes can be regulated and turned on without prior mRNA synthesis Signup and view all the answers

What is the primary function of snRNA in the spliceosome during the splicing process?

To facilitate the recognition of splice sites Signup and view all the answers

Which of the following best describes alternative splicing?

The process of synthesizing multiple mRNAs from a single gene Signup and view all the answers

Which of the following is a key catalytic step in the splicing mechanism mediated by the spliceosome?

Formation of a lariat structure from introns Signup and view all the answers

What is the role of U1 snRNP in the assembly of the spliceosome?

Identifying the 5' splice site of pre-mRNA Signup and view all the answers

Which statement best reflects the mechanism by which the spliceosome operates during RNA splicing?

It utilizes both snRNA and protein components for splicing Signup and view all the answers

What function does snRNA serve in the spliceosome?

To facilitate the recognition of splice junctions Signup and view all the answers

What is a key benefit of alternative splicing in mRNA processing?

It allows for a single gene to produce multiple protein variants Signup and view all the answers

During the splicing reaction, what happens after the first cut is made by the spliceosome?

The lariat structure is formed and sealed Signup and view all the answers

Which complex is formed when U1 and U2 snRNPs associate with the splice sites?

Complex A Signup and view all the answers

What is the overall purpose of the spliceosome's assembly process?

To ensure the precise excision of introns and joining of exons Signup and view all the answers

What type of RNA is primarily responsible for the catalytic activity in the spliceosomal process?

snRNA Signup and view all the answers

Which helicases are crucial for the formation of the pre-spliceosome complex?

Prp5 and Sub2 Signup and view all the answers

What is formed from the lariat structure after the splicing process?

A degraded intron Signup and view all the answers

What represents a significant distinction between snRNA and mRNA processing?

snRNA processing involves specialized snRNPs for splicing Signup and view all the answers

How does the spliceosome ensure precise splicing during RNA processing?

Through complementary base pairing with intron sequences Signup and view all the answers

What is the primary role of RNA helicases during spliceosome activation?

To facilitate the release of certain snRNP components Signup and view all the answers

Which spliceosomal complex is formed after the first catalytic step?

Complex C Signup and view all the answers

What distinguishes exon-defined spliceosomes from intron-defined spliceosomes?

They undergo a process of rearrangement during activation. Signup and view all the answers

What role do Splicing Regulatory Elements (SREs) play in mRNA processing?

They can promote or inhibit splicing based on their configuration. Signup and view all the answers

During splicing, what is the functional significance of the lariat structure?

It aids in the process of exon splicing and intron release. Signup and view all the answers

What happens to the snRNPs U2, U5, and U6 after splicing is complete?

They are released from the post-spliceosomal complex. Signup and view all the answers

How does alternative splicing increase protein diversity?

By allowing the exclusion or inclusion of different exons. Signup and view all the answers

What unique feature is observed in the maturation process of human exon-defined spliceosomes?

They display a series of regulated mechanistic steps. Signup and view all the answers

What is the effect of cis-regulatory elements on splice site selection?

They can both enhance and suppress splicing decisions. Signup and view all the answers

What does the release of spliced mRNA via helicase Prp22 signify?

The conclusion of the splicing cycle. Signup and view all the answers

Study Notes

SNRNA and mRNA

SNRNAs and mRNAs are very similar in structure and regulation
Both have upstream and downstream sequences that control processing
SNRNAs and mRNAs are both transcribed by RNA polymerase II

Distal and Proximal Sequence Elements in SNRNA

Distal sequence elements (DSEs) are similar to enhancers and increase the affinity of RNA polymerase for the promoter
Proximal sequence elements are similar to promoters and specify the location for RNA polymerase binding

SNRNA and mRNA Transcription

SNRNA can be transcribed independently of mRNA
SNRNA can be transcribed even when mRNA is not needed
SNRNA can play a role in processing the mRNA transcribed before it

SNRNA Function

SNRNAs are small, nuclear RNAs that are part of the spliceosome
SNRNAs are involved in the splicing process (cutting and joining RNA sequences)
SNRNAs are critical for processing mRNA molecules

Splicing

mRNAs need SNRNAs to be processed
In splicing, introns are removed from mRNA and exons are joined together
Small nuclear ribonucleoproteins (SNRNPs) are composed of SNRNA and proteins
SNRNPs are the functional units of splicing and determine where the splice occurs

SNRNP Function

Different SNRNAs identify and bind to different splice sites
SNRNPs are required for catalytic activity and splicing

Intron Removal

Introns are removed during splicing
Intron removal is a regulated process to prevent the destruction of all mRNA molecules
The lariat structure that forms after initial splicing signals for the removal of introns

Regulation of RNA Processing

Splicing involves both nuclear and cytoplasmic components
SNRNAs are exported from the nucleus, processed in the cytoplasm, and then reimported to the nucleus
This process helps regulate splicing and ensures that only appropriate SNRNAs are involved in splicing

Upstream and Downstream Elements in mRNA and snRNA

Similar arrangement in DNA for both mRNA and snRNA
DSE (distal sequence element) acts as enhancer
PSE (proximal sequence element) acts as promoter

snRNA Processing

LEC (little elongation complex) for snRNA
GTFs (general transcription factors) are involved
SNAPc (snRNA-activating protein complex) is used

mRNA Processing

SEC (super elongation complex) for mRNA
Splicing factors
Spliceosome is used

snRNA Function

Essential for spliceosome function
Undergoes additional processing to become functional
Requires both cytoplasmic and nuclear steps, including export and import

Spliceosome

Contains proteins and specialized snRNAs
snRNAs base pair with splice junctions for specificity
snRNAs combine with proteins to form snRNPs
snRNPs U1, U2, and U5 recognize splice donor and acceptor sites

Splicing Process

5' exon moves to 3' splice acceptor site
Second cut is made by spliceosome
Exon termini join and seal, forming a lariat structure
Lariat is degraded
Spliced mRNA contains fused exons with coding information

Alternative Splicing

Enables production of multiple products from the same sequence
Increases variety in products
Same regulatory control mechanisms for transcription
Provides additional regulatory or functional control at the transcript processing level

Spliceosome Assembly and Activity

Occurs at sites of transcription
Rearrangement spans neighboring intron
snRNA associates with pre-processed mRNA transcript
Forms pre-spliceosome complex A
Requires helicases Prp5 and Sub2

Spliceosome Assembly Stages

U1 and U2 snRNPs associate with 5' and 3' splice sites, forming complex A (pre-spliceosome)
Complex B formed by the addition of U4/U6 and U5 snRNPs
Complex B is catalytically active and requires multiple RNA helicases
U4 and U1 are released, forming lariat precursor and complex C
Complex C carries out the second catalytic step, forming the post-spliceosomal complex

Post-Spliceosomal Complex

snRNPs U2, U5, and U6 are released
Lariat intron is released and exons are spliced
Spliced particle (mRNA) is released via helicase Prp22

Exon vs. Intron Spliceosomes

Exons are smaller than introns in vertebrates
ED (Exon Defined) spliceosomes form first, then rearrange to ID (Intron Defined) spliceosomes

Cryo-electron Microscopy of Spliceosomes

Showed 4 unique states of ED spliceosomes
Implies a maturation process for spliceosomes
Provides insights into canonical splicing, back-splicing, and exon skipping

Regulation of Alternative Splicing

Combination of cis-regulatory elements and trans-acting factors
Cis-acting regulatory elements (SREs): ESE, ISE, ESS, or ISS; can promote or prevent splicing
Trans-acting splicing factors: recruited to the site by SREs
Activity of factors depends on the situation

Differences Between Prokaryotic and Eukaryotic Gene Sequences

Prokaryotes have colinear genes (no introns), while eukaryotes have split genes (contain introns)
Prokaryotic mRNA is translated immediately after transcription, while eukaryotic mRNA undergoes processing before translation

Key Terms

Deamination: Loss of an amino group from a molecule
Colinear: Genes where the sequence of nucleotides directly corresponds to the sequence of amino acids in the protein product
Split: Genes with non-coding sequences (introns) interspersed between coding sequences (exons)
Polyadenylation: Addition of a poly(A) tail to the 3' end of a transcript
Methyltransferase: Enzyme that adds a methyl group to a molecule
Exon: Coding sequence within a gene
Intron: Non-coding sequence within a gene
Lariat: Loop structure formed during splicing
snRNA: Small nuclear RNA, involved in splicing
snRNP: Small nuclear ribonucleoprotein, complex of snRNA and protein
Spliceosome: Complex of snRNPs and proteins that removes introns from pre-mRNA
Upstream Elements: Sequences located before (upstream) a gene's coding region, important for transcription
Downstream Elements: Sequences located after (downstream) a gene's coding region, important for transcription
Regulatory Elements: Sequences that control the expression of a gene

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Description

Explore the similarities and differences between SNRNA and mRNA in this quiz. Delve into their transcription processes, regulatory elements, and functional roles in splicing. Test your understanding of these essential molecular components involved in gene expression.