Q: The Dscam gene in Drosophila can produce 38,016 different protein isoforms. If each mRNA contains one of 12 possible exons for exon 4, one of 48 for exon 6, one of 33 for exon 9, and one of 2 for exon 17, which equation correctly calculates the number of possible isoforms?

$$38,016 = 12 \times 48 \times 33 \times 2$$

Question 1

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

Accepted Answer

It increases the number of protein isoforms produced from a single gene.

Question 2

A mutation occurs in an intronic splicing enhancer (ISE) of a gene. What is the most likely consequence?

Accepted Answer

Exon skipping or intron retention, potentially leading to a non-functional protein.

Question 3

Which of the following is a direct result of phosphorylation as a post-translational modification?

Accepted Answer

A conformational change in the protein that can alter its activity.

Question 4

The Dscam gene in Drosophila can produce 38,016 different protein isoforms. If each mRNA contains one of 12 possible exons for exon 4, one of 48 for exon 6, one of 33 for exon 9, and one of 2 for exon 17, which equation correctly calculates the number of possible isoforms?

Accepted Answer

$$38,016 = 12 	imes 48 	imes 33 	imes 2$$

Question 5

Which of the following mechanisms is NOT a form of posttranscriptional regulation?

Accepted Answer

Chromatin remodeling

Question 6

A patient with Spinal Muscular Atrophy (SMA) has a mutation in the SMN2 gene that affects a splicing enhancer site. What is the molecular consequence of this mutation?

Accepted Answer

Most SMN2 transcripts exclude exon 7, resulting in a non-functional or less functional protein.

Question 7

Which of the following best explains how the drug Spinraza (nusinersen) treats SMA at the molecular level?

Accepted Answer

It blocks an intronic splicing silencer, increasing exon 7 inclusion in SMN2 transcripts.

Question 8

Which of the following statements about mRNA stability is correct?

Accepted Answer

Binding of poly-A binding protein stabilizes the poly-A tail and increases mRNA stability.

Question 9

Which of the following is a function of non-coding RNAs (ncRNAs) in posttranscriptional regulation?

Accepted Answer

They regulate gene expression by repressing translation or triggering mRNA degradation.

Question 10

Which of the following best describes the mechanism of RNA interference (RNAi)?

Accepted Answer

Short double-stranded RNAs are processed by Dicer, loaded onto RISC, and guide mRNA cleavage or translational repression.

Question 11

A mutation in an exonic splicing silencer (ESS) would most likely result in which of the following?

Accepted Answer

Increased inclusion of the affected exon in the mature mRNA.

Question 12

Which of the following is true regarding ubiquitin-mediated protein degradation?

Accepted Answer

Ubiquitinated proteins are targeted to the proteasome for degradation into small peptides.

Question 13

Which of the following best explains why the number of proteins in humans greatly exceeds the number of protein-coding genes?

Accepted Answer

Alternative splicing allows a single gene to produce multiple protein isoforms.

Question 14

Which of the following is a real-world example of posttranscriptional regulation affecting human health?

Accepted Answer

Spinal Muscular Atrophy caused by abnormal splicing of the SMN2 gene.

Question 15

Which of the following best describes the role of SR proteins in splicing?

Accepted Answer

They bind to splicing enhancers and recruit spliceosome components to activate splicing.

Question 16

If SRSF10 is predominantly expressed in the nervous system and binds to the ISS-N1 site of the SMN2 transcript, what is the expected effect on SMND7 transcript levels in the spinal cord compared to skin cells?

Accepted Answer

There would be more SMND7 transcripts in the nervous system than in skin cells.

Question 17

Which of the following is a correct statement about the regulation of mRNA degradation?

Accepted Answer

Deadenylation-dependent decay involves shortening of the poly-A tail by exoribonucleases.

Question 18

Which of the following is an example of a cis-acting sequence involved in alternative splicing?

Accepted Answer

Exonic splicing enhancer (ESE)

Question 19

Which of the following best describes the effect of phosphorylation on the protein TTP in the regulation of TNFα mRNA?

Accepted Answer

Phosphorylated TTP binds to AREs and prevents mRNA degradation, increasing TNFα transcript levels.

Chap 18

Study Guide - Practice Questions

Study Guide - Flashcards