Q: Which of the following equations correctly represents the reaction catalyzed by β-galactosidase?

$$\text{Lactose} + H_2O \xrightarrow{\beta\text{-Galactosidase}} \text{Galactose} + \text{Glucose}$$

Question 1

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

Accepted Answer

It encodes enzymes for the metabolism of lactose.

Question 2

A mutation in the lacY gene would most likely result in which phenotype in E. coli?

Accepted Answer

Lactose cannot be transported into the cell.

Question 3

Which of the following equations correctly represents the reaction catalyzed by β-galactosidase?

Accepted Answer

$$	ext{Lactose} + H_2O \xrightarrow{\beta	ext{-Galactosidase}} 	ext{Galactose} + 	ext{Glucose}$$

Question 4

In the absence of lactose, what is the state of the lac operon in wild-type E. coli?

Accepted Answer

The repressor is bound to the operator, blocking transcription.

Question 5

A mutation in the lacI gene that prevents the repressor from binding lactose (lacIS) will result in which phenotype?

Accepted Answer

The operon is always off, regardless of lactose presence.

Question 6

Which of the following best explains why lacOc mutations are cis-acting while lacI mutations can be trans-acting?

Accepted Answer

lacOc mutations affect only the operator they are physically linked to, while lacI encodes a diffusible repressor protein.

Question 7

What is the effect of high levels of glucose on the lac operon?

Accepted Answer

Little transcription takes place.

Question 8

Which of the following is required for maximal transcription of the lac operon?

Accepted Answer

Repressor bound to lactose and CAP bound to CAP site.

Question 9

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

Accepted Answer

It is a repressible operon regulated by the presence of tryptophan.

Question 10

In the absence of tryptophan, what happens to the trp repressor?

Accepted Answer

It cannot bind to the operator, and transcription takes place.

Question 11

Which of the following best describes attenuation in the trp operon?

Accepted Answer

It is a mechanism that prematurely terminates transcription, reducing mRNA production.

Question 12

A mutation prevents the CAP protein from binding to the promoter in the lac operon. What will be the effect on transcription?

Accepted Answer

Transcription will decrease.

Question 13

Which of the following is a real-life example of a repressible system in bacteria?

Accepted Answer

The trp operon in E. coli.

Question 14

Which of the following best describes the role of small noncoding RNAs (sRNAs) in gene regulation?

Accepted Answer

They bind to mRNA and can either block or enable translation.

Question 15

A bacterial cell has a mutation that prevents the formation of the terminator hairpin in the trp operon leader sequence. What is the most likely outcome?

Accepted Answer

The trp operon will be transcribed regardless of tryptophan levels.

Question 16

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It encodes multiple proteins from a single mRNA molecule.

Question 17

Which of the following best describes the effect of glucose on cAMP levels in E. coli?

Accepted Answer

High glucose decreases cAMP levels.

Question 18

Which of the following is an example of a cis-acting regulatory element?

Accepted Answer

The operator region of the lac operon.

Question 19

Which of the following scenarios would result in the lac operon being ON (transcribed)?

Accepted Answer

Lactose present, glucose absent.

Regulation of Gene Expression in Bacteria: The lac and trp Operons

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