Question 1

Which of the following best describes transcriptional control of gene expression in prokaryotes?

Accepted Answer

It prevents the synthesis of mRNA from DNA by blocking RNA polymerase binding to the promoter.

Question 2

In the context of the lac operon, what is the role of the lacI gene product?

Accepted Answer

It acts as a repressor that binds to the operator to prevent transcription of lacZ and lacY in the absence of lactose.

Question 3

Which of the following scenarios would result in the highest expression of the lac operon in E. coli?

Accepted Answer

Only lactose is present in the environment.

Question 4

A mutant E. coli strain produces β-galactosidase and galactoside permease even when lactose is absent. Which gene is most likely mutated?

Accepted Answer

lacI

Question 5

Which of the following statements about post-translational control is correct?

Accepted Answer

It is the fastest form of gene regulation but is energetically expensive.

Question 6

Which experimental result would support the hypothesis that glucose inhibits the expression of the lac operon?

Accepted Answer

No β-galactosidase production when only glucose is present.

Question 7

Which of the following best explains why transcriptional control is considered the most energy-efficient form of gene regulation?

Accepted Answer

It prevents unnecessary synthesis of mRNA and proteins, saving resources.

Question 8

A researcher isolates an E. coli mutant that cannot transport lactose into the cell but can still produce β-galactosidase. Which gene is most likely mutated?

Accepted Answer

lacY

Question 9

Which of the following is an example of negative control of gene expression?

Accepted Answer

A regulatory protein binds to DNA and blocks transcription.

Question 10

Which step in the flow of genetic information is directly regulated by translational control?

Accepted Answer

The synthesis of protein from mRNA

Question 11

Which of the following best describes an inducer in the context of the lac operon?

Accepted Answer

A molecule that binds to the repressor and prevents it from binding to the operator, allowing transcription.

Question 12

Which of the following is a correct sequence of events for lactose metabolism in E. coli when lactose is present and glucose is absent?

Accepted Answer

Lactose enters the cell → binds to repressor → repressor releases operator → lacZ and lacY are transcribed → β-galactosidase and permease are produced.

Question 13

Which of the following best explains why some genes are described as 'constitutively expressed'?

Accepted Answer

They are expressed at a constant rate regardless of environmental conditions.

Question 14

Which of the following is a likely consequence of a mutation that inactivates the lacI gene?

Accepted Answer

The lac operon is expressed continuously, regardless of lactose presence.

Question 15

Which of the following best describes the difference between negative and positive control of gene expression?

Accepted Answer

Negative control involves a repressor protein that blocks transcription, while positive control involves an activator protein that stimulates transcription.

Question 16

A researcher wants to identify E. coli mutants that cannot metabolize lactose. Which two-step process should they use?

Accepted Answer

1. Generate random mutations in E. coli. 2. Use genetic screening to find mutants with defects in lactose metabolism.

Question 17

Which of the following is NOT a mechanism by which translational control can occur?

Accepted Answer

Preventing RNA polymerase from binding to the promoter.

Question 18

Which of the following equations best represents the central dogma of molecular biology as described in the study materials?

Accepted Answer

$$DNA \rightarrow mRNA \rightarrow Protein \rightarrow Activated\ Protein$$

Question 19

Which of the following best explains why post-translational control is considered energetically expensive?

Accepted Answer

It involves the synthesis of proteins that may never be activated, wasting cellular resources.

Prokaryotic Gene Expression and Regulation: The lac Operon Model

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