Question 1

Which of the following best describes the function of the 5' m7G cap added to eukaryotic pre-mRNA?

Accepted Answer

It protects the mRNA from 5' to 3' exonuclease degradation and facilitates translation initiation.

Question 2

A mutation in the branch-point adenosine of an intron would most likely disrupt which step of spliceosomal splicing?

Accepted Answer

Formation of the lariat intermediate via nucleophilic attack by the 2'-OH of the branch-point adenosine.

Question 3

Alternative splicing increases proteome diversity by:

Accepted Answer

Allowing a single gene to produce multiple mRNA isoforms that may encode proteins with different functions.

Question 4

Which of the following is a key difference between group I and group II intron splicing?

Accepted Answer

Group I introns require a free guanosine cofactor, while group II introns use an internal adenosine for the first nucleophilic attack.

Question 5

In the context of Drosophila sex determination, what is the role of the Sex-lethal (Sxl) protein?

Accepted Answer

Sxl acts as a splicing repressor, preventing the use of a default 3' splice site in the transformer (tra) pre-mRNA.

Question 6

A patient with spinal muscular atrophy (SMA) is treated with Spinraza, an antisense oligonucleotide. What is the molecular mechanism by which Spinraza increases functional SMN protein production?

Accepted Answer

It binds to an intronic silencer in SMN2 pre-mRNA, preventing hnRNP-A1 binding and promoting exon 7 inclusion.

Question 7

Which of the following best explains why most SMN2 transcripts do not produce functional SMN protein?

Accepted Answer

A C→T substitution in exon 7 of SMN2 weakens an exonic splicing enhancer, leading to exon 7 skipping.

Question 8

Which of the following is NOT a typical pathway for eukaryotic mRNA degradation?

Accepted Answer

Direct proteasomal degradation of mRNA in the cytoplasm.

Question 9

Which of the following statements about nonsense-mediated decay (NMD) is correct?

Accepted Answer

NMD targets mRNAs with a premature termination codon (PTC) for degradation, preventing production of truncated proteins.

Question 10

Which of the following best describes the role of microRNAs (miRNAs) in posttranscriptional gene regulation?

Accepted Answer

miRNAs guide the RNA-induced silencing complex (RISC) to complementary mRNA sequences, leading to translation repression or mRNA decay.

Question 11

A gene contains 10 exons and 9 introns. If alternative splicing allows for the inclusion or exclusion of each exon (except the first and last), what is the maximum number of possible mRNA isoforms (ignoring other regulatory constraints)?

Accepted Answer

$$2^8 = 256$

Question 12

Which of the following is a function of long noncoding RNAs (lncRNAs) in posttranscriptional regulation?

Accepted Answer

lncRNAs can act as 'sponges' for miRNAs, preventing them from repressing their mRNA targets.

Question 13

Which of the following best explains the effect of phosphorylation on protein function?

Accepted Answer

Phosphorylation induces conformational changes in proteins, often altering their activity or interactions.

Question 14

What is the role of ubiquitin in posttranslational regulation?

Accepted Answer

Ubiquitin tags proteins for degradation by the proteasome.

Question 15

Which of the following is a direct consequence of alternative polyadenylation in mRNA processing?

Accepted Answer

Production of mRNAs with different 3' untranslated regions (UTRs), affecting mRNA stability and regulation.

Question 16

Which of the following statements about the closed-loop model of translation is correct?

Accepted Answer

The 5' cap and 3' poly(A) tail of mRNA interact via cap-binding proteins and poly(A)-binding proteins to enhance translation initiation.

Question 17

Which of the following is a real-life example of a spliceopathy caused by disrupted splicing regulation?

Accepted Answer

Myotonic dystrophy, caused by repeat expansions that disrupt splicing factor function.

Question 18

Which of the following best describes the function of the spliceosome?

Accepted Answer

It catalyzes the removal of introns from pre-mRNA and ligates exons together.

Question 19

Which of the following is a cis-acting element that can regulate alternative splicing?

Accepted Answer

Exonic splicing enhancer (ESE)

Posttranscriptional Regulation in Eukaryotes: Mechanisms and Implications

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