Q: Which of the following equations correctly represents the reaction catalyzed by adenyl cyclase?

$$\mathrm{ATP} \xrightarrow{\text{adenyl cyclase}} \mathrm{cAMP} + 2\mathrm{P_i}}$$

Question 1

A mutation in the DNA-binding domain of the lacI gene results in a repressor protein that cannot bind to the operator. What is the most likely effect on lac operon expression in the presence and absence of lactose?

Accepted Answer

Lac operon will be constitutively expressed regardless of lactose presence.

Question 2

If a mutation occurs in the operator sequence of the lac operon such that the lacI repressor cannot bind, what will be the result?

Accepted Answer

Constitutive expression of the lac operon, regardless of lactose presence.

Question 3

A mutation in the lactose-binding site of the lacI repressor protein prevents lactose from binding. What is the expected outcome for lac operon expression?

Accepted Answer

Lac operon will always be repressed, even if lactose is present.

Question 4

Which of the following best describes the role of the lacI gene product in the lac operon system?

Accepted Answer

It is a trans-acting repressor that can diffuse and regulate multiple operons.

Question 5

Which molecule is preferred by E. coli for energy metabolism when both glucose and lactose are present?

Accepted Answer

Glucose

Question 6

What is the relationship between glucose and cAMP levels in E. coli?

Accepted Answer

When glucose is high, cAMP is low; when glucose is low, cAMP is high.

Question 7

Which of the following equations correctly represents the reaction catalyzed by adenyl cyclase?

Accepted Answer

$$\mathrm{ATP} \xrightarrow{	ext{adenyl cyclase}} \mathrm{cAMP} + 2\mathrm{P_i}}$$

Question 8

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

Accepted Answer

It binds to the promoter and facilitates RNA polymerase binding, increasing transcription.

Question 9

In the presence of both glucose and lactose, what is the expected level of lac operon transcription?

Accepted Answer

Very low or diminished transcription due to catabolite repression.

Question 10

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

Accepted Answer

A repressible operon that is turned off in the presence of tryptophan.

Question 11

What happens to the trp operon when tryptophan is absent from the environment?

Accepted Answer

The repressor cannot bind to the operator, and transcription of the operon occurs.

Question 12

A mutation in the trp repressor protein prevents it from binding to DNA. What is the most likely effect on trp operon expression?

Accepted Answer

Transcription of the trp operon will occur all the time, regardless of tryptophan presence.

Question 13

Which of the following is a function of small noncoding RNAs (sRNAs) in bacteria?

Accepted Answer

They can bind to mRNAs and regulate translation either positively or negatively.

Question 14

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

Accepted Answer

Lactose present, glucose absent

Question 15

Which of the following best explains why the lac operon is considered to be under negative control?

Accepted Answer

A repressor protein binds to the operator to inhibit transcription in the absence of lactose.

Question 16

Which of the following is a correct statement about the regulation of the trp operon?

Accepted Answer

Tryptophan acts as a corepressor, enabling the repressor to bind to the operator and block transcription.

Question 17

Which of the following best describes the effect of glucose on the lac operon?

Accepted Answer

Glucose inhibits adenyl cyclase, lowering cAMP levels and reducing lac operon transcription.

Question 18

A bacterial cell is growing in a medium containing only lactose (no glucose). Which of the following events will occur?

Accepted Answer

High cAMP levels will activate CAP, leading to increased lac operon transcription.

Question 19

Which of the following is an example of a gene that would be expressed constitutively in a bacterial cell?

Accepted Answer

A gene encoding an enzyme required for glycolysis

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

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