Q: Which of the following equations correctly represents the conversion of ATP to cyclic AMP (cAMP) by adenylyl cyclase?

$$\text{ATP} \xrightarrow{\text{adenylyl cyclase}} \text{cAMP} + \text{PP}_i$$

Question 1

Which of the following best describes the function of the operator region in the lac operon?

Accepted Answer

It is a regulatory region to which the repressor protein binds to control transcription.

Question 2

In the lac operon, what would be the effect of a mutation in the lacI gene that prevents the repressor from binding lactose?

Accepted Answer

Transcription would be repressed even in the presence of lactose.

Question 3

Which enzyme is encoded by the lacZ gene, and what is its primary function?

Accepted Answer

β-galactosidase; cleaves lactose into glucose and galactose.

Question 4

A mutation in the operator region (O^c) of the lac operon prevents the repressor from binding. What is the expected outcome?

Accepted Answer

Transcription is constitutive, occurring even without lactose.

Question 5

Which of the following equations correctly represents the conversion of ATP to cyclic AMP (cAMP) by adenylyl cyclase?

Accepted Answer

$$	ext{ATP} \xrightarrow{	ext{adenylyl cyclase}} 	ext{cAMP} + 	ext{PP}_i$$

Question 6

What is the effect of glucose on the lac operon, and which molecule mediates this effect?

Accepted Answer

Glucose decreases cAMP levels, preventing CAP binding and reducing transcription.

Question 7

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

Accepted Answer

It acts as a corepressor, enabling the repressor to bind the operator and inhibit transcription.

Question 8

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

Accepted Answer

A mechanism where transcription is greatly reduced due to formation of a terminator hairpin in the leader region.

Question 9

If a cell is in an environment with high lactose and high glucose, what is the expected level of lac operon expression?

Accepted Answer

Low expression due to catabolite repression by glucose.

Question 10

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is transcribed from multiple genes and encodes multiple proteins.

Question 11

A partial diploid E. coli (merozygote) has one wild-type lac operon and one operon with a mutation in the lacI gene. If lactose is absent, what is the expected outcome?

Accepted Answer

The wild-type operon will be repressed, but the mutant operon will be constitutively expressed.

Question 12

Which of the following is an example of negative control in gene regulation?

Accepted Answer

Transcription occurs unless it is shut off by a repressor molecule.

Question 13

Which structural gene of the lac operon is responsible for facilitating the entry of lactose into the bacterial cell?

Accepted Answer

lacY

Question 14

What is the expected outcome if the trp repressor protein is mutated so that it cannot bind tryptophan?

Accepted Answer

The trp operon will be constitutively expressed, even in the presence of tryptophan.

Question 15

Which of the following best describes the effect of a nonsense mutation in the lacZ gene?

Accepted Answer

Loss of β-galactosidase activity in the cell.

Question 16

Which statement correctly describes the role of CAP in the regulation of the lac operon?

Accepted Answer

CAP binds to the CAP-binding site and stimulates RNA polymerase binding, promoting transcription.

Question 17

Which of the following scenarios would result in maximal expression of the lac operon?

Accepted Answer

Lactose present, glucose absent, CAP bound to CAP-binding site.

Question 18

Which of the following best explains why the trp operon is considered a repressible system?

Accepted Answer

It is repressed in the presence of its end product, tryptophan.

Question 19

What is the consequence of ribosome stalling at the tryptophan codons in the leader region of the trp operon?

Accepted Answer

Formation of the antiterminator hairpin and continued transcription.

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

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