Question 1

Which of the following best describes the role of introns in eukaryotic gene expression?

Accepted Answer

Introns are noncoding regions that are removed from pre-mRNA during splicing, allowing exons to be joined and form mature mRNA.

Question 2

A mutation occurs at the branch point sequence of an intron. What is the most likely consequence?

Accepted Answer

Splicing is prevented, leading to intron retention and possible exon loss.

Question 3

Which consensus sequence is typically found 14–45 nucleotides upstream of the 3' splice site in yeast and is essential for splicing?

Accepted Answer

$$UACUAAC$$

Question 4

What is the function of the spliceosome in mRNA processing?

Accepted Answer

It removes introns from pre-mRNA and joins exons together to form mature mRNA.

Question 5

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

Accepted Answer

U1 snRNA

Question 6

Alternative splicing can result in which of the following outcomes?

Accepted Answer

Proteins with different cellular localizations, activities, or stabilities.

Question 7

A mutation in the acceptor site of an intron most likely leads to which of the following?

Accepted Answer

Intron retention and possible exon loss in the mature mRNA.

Question 8

Which of the following is the correct order of events in eukaryotic mRNA processing?

Accepted Answer

5' capping, splicing, polyadenylation, export to cytoplasm

Question 9

Which sequence acts as the signal for polyadenylation in eukaryotic mRNA?

Accepted Answer

$$AAUAAA$$

Question 10

What is the primary function of the polyA tail in eukaryotic mRNA?

Accepted Answer

It protects mRNA from degradation and increases stability.

Question 11

Which of the following mechanisms allows for rapid regulation of gene expression in eukaryotic cells?

Accepted Answer

Controlling mRNA stability and degradation rates.

Question 12

In a laboratory experiment, you insert a stretch of $$G$$ nucleotides into an mRNA and observe accumulation of intermediate degradation products. What does this indicate about the major route of mRNA decay?

Accepted Answer

5' to 3' decay is the major route.

Question 13

Which enzyme complex is primarily responsible for 5' to 3' mRNA degradation in eukaryotes?

Accepted Answer

Xrn1

Question 14

What is the role of microRNAs (miRNAs) in gene regulation?

Accepted Answer

They bind to complementary mRNA sequences and mediate silencing or degradation.

Question 15

Which of the following is a consequence of a mutation that causes intron retention in mature mRNA?

Accepted Answer

Possible frame shift and premature stop codon in the translated protein.

Question 16

Which of the following statements about mRNA stability is TRUE?

Accepted Answer

mRNA stability can be regulated by elements in both coding and noncoding regions.

Question 17

A patient is diagnosed with a genetic disease caused by abnormal mRNA stability. Which of the following is a plausible molecular explanation?

Accepted Answer

A mutation in an mRNA destabilizing element leads to increased degradation of a critical transcript.

Question 18

Which of the following is NOT a function of RNA-binding proteins (RBPs) in eukaryotic cells?

Accepted Answer

Catalyzing DNA replication.

Question 19

Which of the following best explains why mRNA degradation provides a faster response in gene regulation compared to transcriptional control?

Accepted Answer

Degrading existing mRNAs quickly reduces protein production without waiting for transcription to stop.

Question 20

Which of the following is a key difference between eukaryotic and prokaryotic mRNA stability?

Accepted Answer

Eukaryotic mRNAs are protected by a 5' cap and polyA tail, while prokaryotic mRNAs lack these features.

RNA Processing and mRNA Stability in Eukaryotes

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