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

Allolactose, an isomer of lactose, binds to the repressor protein, causing a conformational change that prevents it from binding the operator.

Question 2

A mutation in the lacY gene of E. coli would most likely result in which of the following phenotypes?

Accepted Answer

The cell cannot transport lactose into the cell, even if the lac operon is induced.

Question 3

Which of the following statements about the trp operon is correct?

Accepted Answer

The trp operon is repressed when tryptophan binds to the trp repressor, enabling it to bind the operator.

Question 4

In a partial diploid E. coli cell with the genotype $$I^+O^cZ^+Y^-/F'I^+O^+Z^-Y^+$$, which of the following best describes the expression of the lac operon genes?

Accepted Answer

lacZ will be constitutively expressed from the chromosome, and lacY will be expressed only in the presence of inducer from the plasmid.

Question 5

Which of the following best explains the effect of glucose on the lac operon in E. coli?

Accepted Answer

Glucose inhibits adenylyl cyclase, lowering cAMP levels and reducing CAP activation, thereby repressing lac operon transcription.

Question 6

A superrepressor mutation ($$I^s) in $$the lac operon results in which of the following outcomes?

Accepted Answer

The lac operon is never expressed, because the repressor cannot be inactivated by the inducer.

Question 7

Which of the following is a key difference between feedback inhibition and genetic repression in bacterial cells?

Accepted Answer

Feedback inhibition affects enzyme activity post-translationally, while genetic repression reduces the synthesis of enzymes at the transcriptional level.

Question 8

Which of the following best describes the function of sigma ($$\sigma) $$factors in bacterial gene regulation?

Accepted Answer

They recognize specific promoter sequences, directing RNA polymerase to initiate transcription of specific sets of genes.

Question 9

Attenuation in the trp operon of E. coli is best described as:

Accepted Answer

A mechanism that regulates gene expression after transcription initiation by forming alternative mRNA secondary structures in the leader sequence.

Question 10

Which of the following statements about riboswitches is correct?

Accepted Answer

Riboswitches are mRNA regions that bind small molecules, causing conformational changes that affect transcription or translation.

Question 11

In the context of eukaryotic gene regulation, what is meant by 'genomic equivalence'?

Accepted Answer

All cells in a multicellular organism contain the same complete set of genes, regardless of their differentiation state.

Question 12

Which of the following best explains why cloning animals, such as Dolly the sheep, is difficult and often results in health problems?

Accepted Answer

The DNA in the donated nucleus often fails to undergo proper epigenetic reprogramming, leading to developmental defects.

Question 13

Which of the following statements about antibody gene rearrangement in lymphocytes is correct?

Accepted Answer

Antibody diversity is generated by rearranging V, D, J, and C gene segments during lymphocyte development.

Question 14

Which of the following is a posttranscriptional mechanism of gene regulation in eukaryotes?

Accepted Answer

Alternative splicing of pre-mRNA.

Question 15

Which of the following best describes the role of chromatin decondensation in eukaryotic gene expression?

Accepted Answer

Decondensation of chromatin exposes promoter regions, allowing transcription to occur.

Question 16

A researcher treats chicken erythrocytes with low levels of DNase I and observes that the globin gene is preferentially degraded. What does this indicate about the chromatin state of the globin gene in these cells?

Accepted Answer

The globin gene is in a decondensed, transcriptionally active state, making it more accessible to DNase I.

Question 17

Which of the following best describes the dual control of the lac operon in E. coli?

Accepted Answer

It is regulated by both negative control (lac repressor) and positive control (CAP-cAMP complex).

Question 18

Which of the following scenarios would most likely result in constitutive expression of the lac operon?

Accepted Answer

A mutation in the operator that prevents repressor binding ($$O^c).$$

Question 19

Which of the following is a real-world application of the CRISPR/Cas system in bacteria?

Accepted Answer

Protection against viral infection by incorporating viral DNA sequences into the bacterial genome and targeting them for cleavage.

Regulation of Gene Expression in Prokaryotes and Eukaryotes

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