$$\text{Lactose} + H_2O \xrightarrow{\text{β-galactosidase}} \text{Glucose} + \text{Galactose}$$

Question 1

Which of the following best describes the function of the lacZ gene in the lac operon?

Accepted Answer

Encodes β-galactosidase, which converts lactose into glucose and galactose.

Question 2

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

Accepted Answer

The repressor binds to the operator, preventing transcription.

Question 3

Which equation represents the catabolic conversion of lactose by β-galactosidase?

Accepted Answer

$$	ext{Lactose} + H_2O \xrightarrow{	ext{β-galactosidase}} 	ext{Glucose} + 	ext{Galactose}$$

Question 4

A constitutive mutation in the operator region of the lac operon would most likely result in:

Accepted Answer

Continuous production of enzymes regardless of lactose presence.

Question 5

Which of the following best describes positive control in bacterial gene regulation?

Accepted Answer

Transcription occurs only when a regulator molecule directly stimulates RNA production.

Question 6

The lac operon is optimally expressed under which condition?

Accepted Answer

In the presence of lactose and the absence of glucose.

Question 7

Which of the following is a function of the lacY gene product?

Accepted Answer

Facilitates the entry of lactose into the bacterial cell.

Question 8

What is the effect of glucose on the expression of the lac operon?

Accepted Answer

Glucose decreases cAMP levels, inhibiting transcription via catabolite repression.

Question 9

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is transcribed from a single promoter and encodes multiple proteins.

Question 10

In the trp operon, what role does tryptophan play in gene regulation?

Accepted Answer

Acts as a corepressor, binding to the repressor and inhibiting transcription.

Question 11

Which of the following best describes the mechanism of CRISPR-Cas adaptive immunity in bacteria?

Accepted Answer

Spacer sequences from phage DNA are inserted into the CRISPR locus, and crRNAs guide Cas nucleases to cleave invading phage DNA.

Question 12

Which equation represents the relationship between cAMP and CAP in lac operon regulation?

Accepted Answer

$$	ext{cAMP} + 	ext{CAP} ightarrow 	ext{cAMP-CAP complex}$$

Question 13

A mutation in the lacI gene that prevents the repressor from binding lactose would result in:

Accepted Answer

Repression of the lac operon even in the presence of lactose.

Question 14

Which of the following is a plausible consequence of removing new spacers from the CRISPR locus in bacteria?

Accepted Answer

Bacteria lose resistance to the specific phage corresponding to the removed spacer.

Question 15

Which of the following best describes a repressible operon?

Accepted Answer

Gene expression is inhibited by the presence of a specific molecule, usually the end product.

Question 16

Which of the following is true about cis-acting and trans-acting elements in operon regulation?

Accepted Answer

Cis-acting elements are DNA sequences, and trans-acting elements are proteins that bind to these sequences.

Question 17

Which step in the CRISPR-Cas mechanism involves the insertion of phage DNA fragments into the CRISPR locus?

Accepted Answer

Spacer acquisition

Question 18

Which of the following is a plausible outcome if the CAP-binding site in the lac operon promoter is mutated?

Accepted Answer

Transcription of the lac operon is diminished even in the absence of glucose.

Question 19

Which of the following best explains why bacteria use inducible enzymes?

Accepted Answer

To adapt to environmental changes by producing enzymes only when specific substrates are present.

Ch 15 Regulation of Gene Expression in Bacteria: The lac Operon, trp Operon, and CRISPR-Cas Systems

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