Question 1

Which of the following best describes the function of introns in eukaryotic genes?

Accepted Answer

They are noncoding regions that are removed from the primary transcript during RNA processing.

Question 2

During mRNA splicing, which consensus sequence is typically found 15-45 nucleotides upstream of the 3' splice site and is essential for branch point recognition?

Accepted Answer

UACUAAC

Question 3

A mutation occurs at the branch site of an intron. What is the most likely consequence for mRNA processing?

Accepted Answer

Intron retention and possible exon loss

Question 4

Which of the following is a correct sequence of events during spliceosome-mediated splicing?

Accepted Answer

U1 snRNP binds to the 5' splice site, U2 snRNP binds to the branch point, U4/U6 and U5 join, U1 and U4 are released, and the spliceosome is activated.

Question 5

Alternative splicing can result in which of the following outcomes?

Accepted Answer

Production of mRNAs with different cellular localizations

Question 6

Which equation correctly represents the exponential decay of mRNA concentration over time after transcription is shut down?

Accepted Answer

$$C(t) = C_0$ e$$^{-kt}$$

Question 7

A deletion mutation in an intron that does NOT introduce a stop codon and is a multiple of 3 nucleotides will most likely result in:

Accepted Answer

An insertion in the protein sequence without a premature stop

Question 8

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

Accepted Answer

Eukaryotic mRNA is stabilized by a poly(A) tail, while prokaryotic mRNA generally lacks a poly(A) tail.

Question 9

Which protein complex is responsible for the majority of mRNA degradation in eukaryotes after deadenylation?

Accepted Answer

Exosome

Question 10

A researcher inserts a stretch of G nucleotides into an mRNA and observes accumulation of $$[GGGGG-	ext{A}_{10}]$$ intermediates. What does this indicate about the directionality of mRNA degradation?

Accepted Answer

Degradation occurs primarily in the 5' to 3' direction.

Question 11

Which of the following is a function of the poly(A) tail in eukaryotic mRNA?

Accepted Answer

It increases mRNA stability by protecting against exonuclease degradation.

Question 12

Which of the following is true regarding microRNA (miRNA)-mediated silencing?

Accepted Answer

miRNAs are loaded into the RNA-induced silencing complex (RISC) and target mRNAs with complementary sequences for degradation or translational repression.

Question 13

Which of the following best explains why mRNA stability is important for gene regulation in eukaryotic cells?

Accepted Answer

It allows rapid changes in protein levels in response to cellular signals.

Question 14

A mutation in the 3' untranslated region (UTR) of an mRNA disrupts a stabilizing element. What is the most likely effect?

Accepted Answer

Decreased mRNA stability and increased degradation

Question 15

Which of the following is NOT a component of the spliceosome?

Accepted Answer

DNA polymerase

Question 16

Which consensus sequence is recognized by the polyadenylation machinery to signal the addition of the poly(A) tail?

Accepted Answer

AAUAAA

Question 17

Which of the following scenarios would most likely result in a frameshift mutation?

Accepted Answer

Insertion of 2 nucleotides into an exon

Question 18

Which equation would you use to calculate the half-life ($$t_{1/2}) of an $$mRNA given its decay rate constant $$k$$?

Accepted Answer

$$t_{1/2} = \frac{\ln 2}{k}$$

Question 19

Which of the following is a biological consequence of mutations in splicing junctions?

Accepted Answer

Intron retention and exon loss

Question 20

Which of the following statements about RNA-binding proteins (RBP) is correct?

Accepted Answer

They tag mRNAs for specific cellular processes, localization, or degradation.

RNA Processing and mRNA Stability in Eukaryotes

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