Q: Which of the following is a correct statement about the central dogma of molecular biology?

$$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$$

Question 1

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

Accepted Answer

It encodes enzymes required for the breakdown and utilization of lactose as an energy source.

Question 2

What is the role of the CAP-cAMP complex in the regulation of the lac operon?

Accepted Answer

It acts as a positive regulator by enhancing the binding of RNA polymerase to the promoter.

Question 3

Which of the following conditions will result in the highest expression of the lac operon?

Accepted Answer

Lactose present, glucose absent

Question 4

A mutation in the lacO operator site (lacOc) leads to which phenotype?

Accepted Answer

Constitutive expression of the lac operon, regardless of lactose presence

Question 5

Which enzyme is responsible for converting lactose into allolactose, the true inducer of the lac operon?

Accepted Answer

β-galactosidase

Question 6

What is the effect of a lacI- mutation (loss of function in the lac repressor gene)?

Accepted Answer

Constitutive expression of the lac operon

Question 7

Which of the following best explains why the lac operon is not highly expressed when both glucose and lactose are present?

Accepted Answer

Low cAMP levels prevent CAP from binding to DNA, so RNA polymerase does not efficiently bind the promoter.

Question 8

Which of the following is a correct statement about the central dogma of molecular biology?

Accepted Answer

$$	ext{DNA} ightarrow 	ext{RNA} ightarrow 	ext{Protein}$$

Question 9

A super-repressor mutation (lacIS) in the lacI gene results in which of the following?

Accepted Answer

The repressor cannot bind allolactose and always blocks transcription, even when lactose is present.

Question 10

Which of the following best describes the function of the sigma factor in bacterial transcription?

Accepted Answer

It directs RNA polymerase to specific promoter sequences to initiate transcription.

Question 11

Which of the following is an example of positive regulation of gene expression in the lac operon?

Accepted Answer

CAP-cAMP complex binding upstream of the promoter to enhance RNA polymerase binding

Question 12

If a mutation prevents the lacY gene from being expressed, what is the most likely consequence for lactose metabolism?

Accepted Answer

Lactose cannot efficiently enter the cell, so the operon is not strongly induced.

Question 13

Which of the following best describes the concept of 'cis-dominance' as it applies to the lac operon?

Accepted Answer

A mutation in the operator affects only the expression of genes on the same DNA molecule.

Question 14

Which of the following equations correctly represents the breakdown of lactose by β-galactosidase?

Accepted Answer

$$	ext{Lactose} \xrightarrow{\beta	ext{-galactosidase}} 	ext{Glucose} + 	ext{Galactose}$$

Question 15

Which of the following statements about transcription factors in bacteria is correct?

Accepted Answer

Repressors bind to operator sequences to block transcription, while activators bind to specific sites to enhance transcription.

Question 16

A researcher adds both glucose and lactose to a culture of E. coli. Which of the following best describes the expected transcriptional activity of the lac operon?

Accepted Answer

Basal (very low) transcription due to low cAMP and inactive CAP.

Question 17

Which of the following is a real-world application of understanding the lac operon system?

Accepted Answer

Using inducible promoters in biotechnology to control gene expression in engineered bacteria.

Question 18

Which of the following best explains why a small amount of β-galactosidase is always present in E. coli, even in the absence of lactose?

Accepted Answer

The lac operon is expressed at a basal level due to occasional dissociation of the repressor from the operator.

Regulation of Gene Expression in Bacteria: The lac Operon Model

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