Question 1

Which of the following best describes the difference between cis-acting regulatory sequences and trans-acting regulatory proteins in eukaryotic gene regulation?

Accepted Answer

Cis-acting regulatory sequences are DNA elements that regulate transcription of genes on the same chromosome, while trans-acting proteins are diffusible factors that can bind to target sequences on any chromosome.

Question 2

A mutation deletes the locus control region (LCR) near the human $\beta$-globin gene complex. What is the most likely consequence of this mutation?

Accepted Answer

Expression of the $\beta$-globin complex genes will be abnormally regulated, potentially leading to thalassemia.

Question 3

In the yeast galactose utilization pathway, which protein acts as a repressor in the presence of glucose, and what is its mechanism?

Accepted Answer

Mig1; it binds a silencer sequence and recruits Tup1 to form a repressor complex that prevents transcription initiation.

Question 4

Which of the following statements about enhancer sequences is TRUE?

Accepted Answer

Enhancer sequences can be located far upstream, downstream, or even within the genes they regulate.

Question 5

A researcher finds that a DNA sequence acts as an enhancer in one tissue but as a silencer in another. What is the most likely explanation for this observation?

Accepted Answer

Different regulatory proteins are present and bind to the sequence in each tissue.

Question 6

Which of the following best explains the role of pioneer factors in eukaryotic transcriptional regulation?

Accepted Answer

Pioneer factors are the first to bind regulatory molecules, facilitating the binding of additional transcription factors.

Question 7

In the regulation of the GAL genes in yeast, what is the effect of galactose on the Gal4/Gal80 system?

Accepted Answer

Galactose binds Gal80, causing it to release Gal4, which then binds UAS$_G$ and activates transcription.

Question 8

Which equation best represents the relationship between the number of transcription factors ($n$) and the number of possible regulatory outputs ($O$) for a modular enhancer with $m$ binding sites?

Accepted Answer

$O = 2^m$

Question 9

Why are insulator sequences important in eukaryotic gene regulation?

Accepted Answer

They prevent enhancers from activating non-target genes by forming DNA loops that isolate specific promoter regions.

Question 10

A patient with thalassemia is found to have no mutations in the $\alpha$- or $\beta$-globin genes or their promoters. What is a plausible genetic explanation for their disease?

Accepted Answer

A deletion or rearrangement affecting the locus control region (LCR) near the globin gene complex.

Question 11

Which of the following is a real-world example of tissue-specific enhancer action?

Accepted Answer

The Sonic hedgehog (SHH) gene is regulated by different enhancers in brain and limb tissues, resulting in tissue-specific expression.

Question 12

Which statement about the $\beta$-globin locus control region (LCR) is correct?

Accepted Answer

The LCR contains four distinct sequences (HS1-HS4) that bind regulatory proteins and direct DNA looping to the promoters of the globin genes.

Question 13

Which of the following best describes the function of the Mediator complex in yeast GAL gene regulation?

Accepted Answer

It is an enhanceosome that forms a DNA loop, allowing contact between the UAS$_G$-bound Gal4 and the general transcription apparatus at the GAL gene promoters.

Question 14

Which of the following is a consequence of enhancer sequence conservation among mammals?

Accepted Answer

It allows for evolutionary constraint on enhancer diversification, ensuring regulation of genes controlling vertebrate body plan development.

Question 15

Which of the following is NOT a mechanism by which eukaryotic repressors inhibit transcription?

Accepted Answer

Activating the formation of enhanceosomes at enhancer sequences.

Question 16

In the yeast GAL system, which equation best describes the probability $P$ of GAL gene transcription occurring in the presence of galactose, assuming Gal4 and Gal3 are present and Gal80 is not bound to Gal4?

Accepted Answer

$P = 1$

Question 17

Which of the following scenarios would most likely result in the failure of a tissue-specific gene to be expressed?

Accepted Answer

A mutation in the tissue-specific enhancer that prevents binding of the required transcription factors.

Question 18

Which of the following is TRUE regarding the modularity of eukaryotic regulatory sequences?

Accepted Answer

Modules in enhancers and silencers allow integration of activities from different transcription factors, producing different regulatory outputs.

Regulation of Gene Expression in Eukaryotes: Cis- and Trans-Acting Elements, Enhancers, Silencers, and Model Systems

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