lecture 11

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Questions and Answers

What is the function of the 5' cap in eukaryotic mRNA processing?

It promotes splicing of introns.

It protects mRNA from degradation. (correct)

It adds additional coding sequences to the mRNA.

It facilitates ribosome binding during translation. (correct)

Alternative splicing allows for which of the following?

The introduction of stop codons in mRNA.

Complete removal of all introns from the pre-mRNA.

The creased formation of multiple ribosomes.

The joining of exons in different combinations. (correct)

How does mRNA degradation contribute to gene regulation?

It influences the expression levels of proteins. (correct)

It leads to the rapid synthesis of new mRNA.

It makes mRNA sequences resistant to splicing.

It permanently silences gene expression.

Which enzyme complex is responsible for splicing eukaryotic pre-mRNA?

Spliceosome Signup and view all the answers

What is the impact of mutations that disrupt splice sites in eukaryotic mRNA?

They result in the production of non-functional proteins. Signup and view all the answers

What role do snRNAs play in RNA processing?

They recognize splice sites and catalyze splicing. Signup and view all the answers

Which mechanism is credited with controlling tissue-specific gene expression?

Alternative splicing Signup and view all the answers

Which of the following describes RNA editing in mRNA processing?

Converting specific bases like Cytosine or Adenosine. Signup and view all the answers

What is the primary role of tRNAs in translation?

To align amino acids on the mRNA template Signup and view all the answers

During translation initiation, which component first interacts with the mRNA strand?

Initiator tRNA Signup and view all the answers

What distinguishes the initiation of translation in prokaryotes from that in eukaryotes?

The lack of a nucleus in prokaryotes Signup and view all the answers

Which of the following codon types indicates the termination of translation?

Stop codons Signup and view all the answers

What process can allow global translational activity to be regulated?

Modification of translation initiation factors Signup and view all the answers

How many amino acids can be specified by the genetic code?

20 amino acids Signup and view all the answers

What is the function of miRNAs in relation to mRNAs?

They degrade mRNAs Signup and view all the answers

What is the composition of ribosomes in terms of structural and catalytic components?

Structural proteins and rRNA Signup and view all the answers

What is the relationship between the number of SMN2 gene copies and disease phenotype severity?

Three or more copies result in a mild disease phenotype. Signup and view all the answers

When SMN2 is processed, how often is exon 7 treated like an intron?

80% of the time Signup and view all the answers

Which statement correctly explains the difference in processing between SMN2 and SMN1?

The C in SMN1 is essential for the 5' splice site of exon 7. Signup and view all the answers

Which of the following is a potential SMA treatment that works through splicing modification?

Nusinersen, which blocks the removal of exon 7. Signup and view all the answers

What is a primary reason for the variability in mRNA stability in eukaryotic cells?

Mammalian mRNAs have different lifetimes ranging from minutes to hours. Signup and view all the answers

Shorter-lived mRNAs typically code for which type of proteins?

Regulatory proteins Signup and view all the answers

If a eukaryotic cell line is producing abnormally long mRNA molecules, what defect could explain this?

Defective polyadenylation mechanisms. Signup and view all the answers

How does Nusinersen function therapeutically for SMA?

It blocks splicing at the site between exons 7 and 8. Signup and view all the answers

Study Notes

Spinal Muscular Atrophy

Spinal Muscular Atrophy (SMA) is a neurodegenerative disease caused by mutations that disrupt the proper splicing of the Survival Motor Neuron (SMN) gene.
SMA is the most common monogenic cause of death in infants.
SMA results in a truncated (shortened), non-functional SMN protein.
The SMN2 coding region is often duplicated in the genome.
Having 3+ copies of the SMN2 gene leads to a mild disease phenotype.

SMN1 & SMN2

SMN2 is processed differently than SMN1 due to a difference in a single nucleotide.
The C in SMN1 is important for the 5' splice site of exon 7.
The T in SMN2 removes a lariat branchpoint from the intron.

Potential treatments for SMA

Antisplicing morpholino: blocks the splice site between exons 7 and 8
Nusinersen: a short segment of nucleotides that blocks removal of exon 7
ETS: an activator protein that binds the enhancer of the SMN1 gene
Risdiplam: modifies splicing of the transcript to force inclusion of exon 7 in SMN2

mRNA degradation

Prokaryotic mRNA has a half-life of 2-3 minutes.
Eukaryotic mRNA stability varies from minutes to hours.
Mammalian mRNAs have different lifetimes, ranging from less than 30 minutes to approximately 20 hours.
The shorter-lived mRNAs code for regulatory proteins.

Eukaryotic RNA processing

Eukaryotic pre-mRNAs are modified by the addition of a 5' 7-methylguanosine cap and a 3' poly-A tail.
Introns are removed by splicing through the action of the large ribozyme complex called the spliceosome.
The spliceosome recognizes splice sites in the pre-mRNA and catalyzes the splicing reaction.
Exons can be joined in various combinations through alternative splicing.
mRNA sequences can be modified by RNA editing (deamination of Cytosine or Adenosine).
mRNAs in eukaryotic cells are degraded at different rates contributing to control of gene expression.

Eukaryotic RNA processing events

Eukaryotic RNA processing begins while the RNA molecule is being transcribed.
The tail of RNA polymerase II is phosphorylated, which allows processing proteins to assemble.
The 5' cap protects the mRNA from degradation and helps initiate translation.
The 3' polyA tail protects the mRNA from degradation and helps export it from the nucleus.
Splicing of pre-mRNA removes introns, keeps exons.
Splicing is carried out by the spliceosome.
The spliceosome is a complex of proteins and snRNAs.

Alternative splicing

Alternative splicing allows for different combinations of exons.

Protein Synthesis

Translation is literally switching languages.
tRNAs serve as adaptors that align amino acids on the mRNA template.
Peptide bond formation is catalyzed by rRNA in the ribosome.
Translation initiation is different in prokaryotes and eukaryotes.
Translation begins at a start codon and ends at a stop codon.

Ribosomes

Ribosomes are made of structural RNA and catalytic protein.

Ribosomes and Translation

Prokaryotic translation initiation starts with the small subunit and initiator tRNA binding to the Shine-Dalgarno sequence.
Eukaryotic translation initiation involves the small subunit and initiator tRNA binding to the 5' cap, followed by movement to the start codon.
Prokaryotic mRNAs can be polycistronic.

Prokaryotic and Eukaryotic RNA Processing

The difference between prokaryotic and eukaryotic RNA processing and ribosome recognition strategies is NOT a functional implication.

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Description

This quiz explores Spinal Muscular Atrophy (SMA), a severe neurodegenerative condition primarily affecting infants. It covers the genetics behind the disease, including SMN1 and SMN2 genes, as well as potential treatments like Nusinersen and Risdiplam. Test your knowledge on the causes, genetics, and therapeutic approaches to SMA.