Question 1

Which of the following best describes the mechanism by which the lac operon is induced in E. coli when lactose is present?

Accepted Answer

Lactose (or its isomer allolactose) binds to the repressor, causing it to dissociate from the operator, allowing RNA polymerase to transcribe the operon.

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 binds to the repressor, enabling it to bind to the operator and block transcription.

Question 4

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

Accepted Answer

Attenuation is a process 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 structure and a large number of transcription factors, whereas prokaryotes typically use naked DNA and fewer regulatory proteins.

Question 6

DNA methylation in eukaryotes most commonly occurs at which nucleotide sequence, and what is a major biological consequence of this modification?

Accepted Answer

At cytosine residues in CpG dinucleotides, often resulting in gene silencing.

Question 7

Which of the following scenarios best illustrates the concept of genomic imprinting as it relates to DNA methylation?

Accepted Answer

A single parental allele is expressed while the other is silenced by DNA methylation.

Question 8

Which of the following is a direct effect of histone deacetylation on chromatin structure and gene expression?

Accepted Answer

Histone deacetylation strengthens the ionic interactions between DNA and histones, promoting heterochromatin formation and gene repression.

Question 9

A mutation in a eukaryotic cell prevents the phosphorylation of the C-terminal domain (CTD) of RNA polymerase II. Which of the following processes would be most directly affected?

Accepted Answer

The transition from transcription initiation to elongation, as well as the recruitment of RNA processing factors.

Question 10

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 evict nucleosomes, thereby altering chromatin structure and regulating gene accessibility.

Question 11

Which of the following is a mechanism by which translation can be regulated in bacteria?

Accepted Answer

By occlusion of the ribosome binding site due to mRNA secondary structure or binding of regulatory proteins or antisense RNA.

Question 12

In the context of RNA interference, what is the primary function of the RISC complex?

Accepted Answer

To use complementarity to miRNA or siRNA to identify and degrade target mRNA molecules.

Question 13

Which of the following best describes a riboswitch?

Accepted Answer

An mRNA molecule that changes its structure upon binding a specific ligand, thereby regulating its own translation.

Question 14

A patient is found to have a mutation that prevents the deamination of cytidine to uridine in the mRNA for apolipoprotein B. What is the most likely consequence of this mutation?

Accepted Answer

The patient will only produce the longer ApoB-100 protein, as RNA editing to create ApoB-48 will not occur.

Question 15

Which of the following equations correctly represents the relationship between the rate of transcription ($$v$$), the concentration of active RNA polymerase ($$[E]$$), and the concentration of accessible DNA template ($$[S]) in a $$simplified model?

Accepted Answer

$$v = k_{cat} \cdot [E] \cdot [S]$$

Question 16

A researcher treats eukaryotic cells with a drug that inhibits histone acetyltransferases (HATs). Which of the following outcomes is most likely?

Accepted Answer

Decreased acetylation of histones, leading to tighter chromatin and reduced gene expression.

Question 17

Which of the following best explains why 5-azacytidine can be used as a treatment for certain cancers?

Accepted Answer

It inhibits DNA methylation, potentially reactivating silenced tumor suppressor genes.

Question 18

In erythropoietic cells, translation of globin mRNA is regulated by heme levels. Which of the following best describes this regulation?

Accepted Answer

Low heme levels activate a kinase that phosphorylates eIF2, preventing the initiation of translation.

Regulation of Gene Expression (Chapter 26) – Biochemistry: Concepts and Connections

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