mRNA Splicing and Translation Mechanisms

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Questions and Answers

What is the effect of aberrant mRNA splicing on gene expression?

It can lead to the production of dysfunctional proteins. (correct)

It only affects non-coding RNAs.

It has no impact on gene expression.

It enhances gene expression significantly.

How is the translation of ferritin mRNA regulated?

By the expression levels of microRNAs only.

By an increase in cellular temperature.

Through the binding of ribosomes without any cofactors.

By the presence of iron response element binding protein. (correct)

What role does nonsense-mediated decay play in mRNA quality control?

It helps in the synthesis of miRNAs.

It enhances the translation of defective mRNAs.

It eliminates mRNAs that contain premature stop codons. (correct)

It fosters the accumulation of faulty mRNAs.

What is the primary role of the mTOR pathway in cell growth?

It promotes protein synthesis and controls translation. Signup and view all the answers

How do miRNAs regulate mRNA stability and translation?

They target specific mRNAs to inhibit their translation. Signup and view all the answers

What is the term used when a new amino acid is closely related in chemical properties to the original amino acid at a position in a protein?

Conservative substitution Signup and view all the answers

Which of the following describes a nonsense mutation?

A mutation that creates a stop codon Signup and view all the answers

What mechanism allows cells to prevent the translation of potentially toxic truncated proteins resulting from nonsense mutations?

Nonsense mediated decay (NMD) Signup and view all the answers

Why is it difficult to predict the effects of missense mutations?

They depend on factors like amino acid nature and position in the sequence Signup and view all the answers

Which type of amino acid substitution is least likely to disrupt protein function?

Conservative substitution Signup and view all the answers

What can be an outcome of a nonsense mutation in a gene?

Production of functionally impaired proteins Signup and view all the answers

Which codon is NOT considered a nonsense codon?

AUC Signup and view all the answers

What is a common feature of amino acids involved in conservative substitutions?

They possess similar chemical properties Signup and view all the answers

What is the primary function of nonsense-mediated decay (NMD)?

To degrade transcripts containing nonsense mutations or premature stop codons. Signup and view all the answers

What is a likely consequence of an insertion or deletion (INDEL) mutation that is not a multiple of three nucleotides?

It will cause a frame shift in the reading frame. Signup and view all the answers

Why are truncated proteins typically toxic to cells?

They often lack essential functional domains. Signup and view all the answers

What is the probability of encountering a stop codon in a new reading frame after an INDEL mutation?

It occurs approximately once every 20 base pairs. Signup and view all the answers

Which of the following processes can lead to insertion and deletion (INDEL) mutations?

Recombination errors, transposons, and replication errors. Signup and view all the answers

What evolutionary mechanism helps maintain the integrity of open reading frames in protein-coding genes?

The absence of nonsense codons in alternative exons. Signup and view all the answers

Why do INDEL-generated premature stop codons rarely produce truncated proteins?

The quality control mechanisms degrade these proteins. Signup and view all the answers

What is the typical range of sizes for insertion or deletion (INDEL) mutations?

From one or two nucleotides up to thousands of nucleotides. Signup and view all the answers

What is the primary role of Dicer in the processing of miRNAs?

To cleave pre-miRNAs into mature miRNAs Signup and view all the answers

How does the RNA-induced silencing complex (RISC) recognize its target mRNAs?

Through complementarity of miRNA seed sequences Signup and view all the answers

What type of RNA degradation is referred to as Nonsense Mediated Decay (NMD)?

A mechanism that degrades mRNAs with premature stop codons Signup and view all the answers

What is the main function of the proteins that bind to mature miRNAs in the RISC complex?

To guide miRNAs for RNA interference Signup and view all the answers

Which component is responsible for exporting pre-miRNAs from the nucleus to the cytoplasm?

Exportin 5 Signup and view all the answers

What is the consequence of RISC binding to an mRNA target?

Can induce either translational repression or cleavage Signup and view all the answers

What is typically the length of mature miRNAs processed from pre-miRNAs?

21-22 nucleotides Signup and view all the answers

How does the miRNA seed sequence relate to its target mRNA?

It binds to the target mRNA at specific regions for silencing Signup and view all the answers

Which process allows a single gene to produce multiple protein products by utilizing different splice sites?

Alternative use of RNA splice sites Signup and view all the answers

What is a common mechanism that aids in the regulation of mRNA splicing?

Nucleophilic attack by branch point OH groups Signup and view all the answers

Which of the following is not a strategy used by eukaryotic cells to produce multiple transcripts from a single gene?

Frame shifting during DNA transcription Signup and view all the answers

Which component is involved in the nucleophilic attack at the 5’ splice junction during mRNA processing?

The branch point adenosine Signup and view all the answers

What role do alternative polyadenylation sites play in mRNA processing?

They can generate mRNA with different 3’ ends Signup and view all the answers

Which of the following correctly describes the process of frame shifting?

It alters the initial reading frame of mRNA translation Signup and view all the answers

What is the primary function of mRNA splicing in eukaryotic cells?

To remove introns and join exons Signup and view all the answers

Which option is part of the mRNA processing mechanism that does not directly involve splicing?

Alternative start codon usage Signup and view all the answers

Study Notes

Learning Objectives

Understand the impact of alternative mRNA splicing on gene expression and its association with disease.
Recognize how ferritin mRNA translation is influenced by iron response element binding proteins.
Identify the significance of nonsense-mediated decay (NMD) in maintaining mRNA quality control.
Comprehend the global control of translation by the mTOR pathway in various cellular contexts, including cancer.
Describe the synthesis pathway of microRNAs (miRNAs) and their regulatory mechanisms on target mRNAs.
Explain the mechanism of mRNA COVID-19 vaccines.

mRNA Splicing and Alternative Splicing

Eukaryotic genes can generate multiple protein products via alternative RNA splice sites, polyadenylation sites, and translation start/stop codons.
Post-translational cleavage of pro-peptides and ribosomal frame shifting contribute to protein diversity.
Conservative substitutions: mutations that replace amino acids with chemically similar ones can maintain protein function.
Non-conservative substitutions: different chemical properties can significantly alter protein function.
Nonsense mutations create stop codons (UGA, UAA, UAG) that typically result in truncated proteins.
Toxic truncated proteins may compete with wild-type proteins, leading to cellular dysfunction.

Nonsense-Mediated Decay (NMD)

NMD is a cellular mechanism that identifies and degrades mRNAs with premature stop codons to prevent toxic protein synthesis.
The process is crucial for avoiding dysfunctional proteins caused by mutations or improper splicing.
NMD is vital for cellular quality control by managing aberrant transcripts.

Insertions and Deletions (INDELs)

INDELs can result from replication errors or transposons, leading to shifts in the reading frame during translation.
INDELs often generate premature stop codons, increasing the likelihood of producing toxic truncated proteins.
Evolution has preserved open reading frames to minimize the impact of non-sense codons in exons.

MicroRNA (miRNA) Regulation

miRNAs are synthesized as primary transcripts (pri-miRNAs), processed into pre-miRNAs, and exported to the cytoplasm.
Dicer enzyme cleaves pre-miRNAs into mature miRNAs (21-22 nt) that form complexes with Argonaute proteins, creating the RNA-induced silencing complex (RISC).
RISC identifies target mRNAs through complementarity, facilitating either translational repression or cleavage depending on binding characteristics.

mRNA Decay Mechanisms

Both specific (NMD) and general pathways exist for RNA degradation, critically regulating gene expression levels.
NMD specifically checks for nonsense codons in mRNAs to initiate degradation, safeguarding against faulty protein production.

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Description

Explore the complexities of mRNA splicing and its role in gene expression. This quiz covers alternative splicing, translation regulation, and the impact of mRNA decay mechanisms. Additionally, it examines how these processes are linked to diseases and the function of COVID-19 vaccines.