Question 1

Which of the following best describes the mechanism by which the lac operon is regulated in the presence of lactose?

Accepted Answer

Lactose acts as an inducer by binding to the repressor, causing it to dissociate from the operator and allowing transcription.

Question 2

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is an mRNA molecule that contains multiple coding sequences, each of which can be translated into a different protein.

Question 3

In the trp operon, what is the role of tryptophan in regulating gene expression?

Accepted Answer

Tryptophan acts as a co-repressor, binding to the repressor protein and enabling it to bind the operator, thus inhibiting transcription.

Question 4

Which of the following best explains the mechanism of attenuation in the trp operon?

Accepted Answer

Attenuation is a regulatory mechanism where the formation of a specific stem-loop structure in the mRNA leader region causes premature termination of transcription when tryptophan levels are high.

Question 5

Which of the following is a key difference between transcriptional regulation in eukaryotes and prokaryotes?

Accepted Answer

Eukaryotic transcriptional regulation involves chromatin remodeling and a large number of transcription factors, whereas prokaryotes typically regulate transcription at the level of operons without chromatin.

Question 6

DNA methylation in eukaryotes most commonly occurs at which nucleotide sequence, and what is its typical effect on gene expression?

Accepted Answer

At CpG dinucleotides, leading to gene silencing.

Question 7

Which of the following scenarios best illustrates the concept of genomic imprinting?

Accepted Answer

A gene is expressed only from the allele inherited from the mother, while the paternal allele is silenced by DNA methylation.

Question 8

Which of the following best describes the function of chromatin remodeling complexes in eukaryotic gene regulation?

Accepted Answer

They use ATP hydrolysis to reposition or restructure nucleosomes, making DNA more or less accessible to transcription factors.

Question 9

A mutation prevents the phosphorylation of the C-terminal domain (CTD) of RNA polymerase II. Which process would be most directly affected?

Accepted Answer

The transition from transcription initiation to elongation would be impaired.

Question 10

Which of the following is a direct consequence of DNA methylation in the promoter region of a gene?

Accepted Answer

Transcription of the gene is repressed due to reduced binding of transcription factors.

Question 11

In bacteria, which mechanism allows for the regulation of translation by antisense RNA?

Accepted Answer

Antisense RNA base-pairs with the target mRNA, preventing ribosome binding and translation.

Question 12

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

Accepted Answer

miRNAs are processed and incorporated into the RISC complex, where they guide the complex to complementary mRNA targets for degradation or translational repression.

Question 13

A patient is found to have a mutation that prevents the formation of the 3-4 stem-loop structure in the trp operon leader mRNA. What is the most likely consequence?

Accepted Answer

Transcription of the trp operon will continue even when tryptophan levels are high.

Question 14

Which of the following is a characteristic of riboswitches?

Accepted Answer

They are mRNA elements that change conformation upon ligand binding, thereby regulating gene expression at the level of translation or transcription.

Question 15

Which of the following best explains how RNA editing can alter protein function in mammals?

Accepted Answer

RNA editing can change specific nucleotides in mRNA, resulting in the production of proteins with altered amino acid sequences.

Question 16

In eukaryotic cells, which process is most directly responsible for the inactivation of one X chromosome in females?

Accepted Answer

DNA methylation of CpG islands on one X chromosome leads to its inactivation.

Question 17

Which of the following equations best represents the energy requirement for chromatin remodeling by ATPase-containing complexes?

Accepted Answer

$$ \mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i} $$

Question 18

A researcher treats cells with a histone deacetylase inhibitor. What is the most likely effect on gene expression?

Accepted Answer

Increased acetylation of histones, leading to a more open chromatin structure and increased gene expression.

Question 19

Which of the following best describes the effect of phosphorylation of eukaryotic initiation factors in erythropoietic cells under low heme conditions?

Accepted Answer

Phosphorylation inhibits initiation factors, reducing translation of globin mRNA.

Regulation of Gene Expression: Mechanisms in Prokaryotes and Eukaryotes

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