Question 1

Why do bacteria primarily rely on transcriptional regulation to control gene expression?

Accepted Answer

It allows bacteria to conserve energy by only producing proteins when needed.

Question 2

Which of the following best describes negative control of the lac operon?

Accepted Answer

A repressor protein binds to the operator, blocking RNA polymerase from transcribing the genes.

Question 3

What would be the consequence of a mutation that inactivates the lac repressor protein?

Accepted Answer

The lac operon would be transcribed continuously, even in the absence of lactose.

Question 4

Which enzyme is responsible for transporting lactose into the E. coli cell?

Accepted Answer

Galactoside permease

Question 5

How does glucose regulate the lac operon through inducer exclusion?

Accepted Answer

Glucose inhibits galactoside permease, preventing lactose from entering the cell.

Question 6

Which of the following is TRUE about the trp operon compared to the lac operon?

Accepted Answer

The trp operon is repressible, while the lac operon is inducible.

Question 7

If a mutation prevents the lac repressor from binding to the operator, what will happen in the absence of lactose?

Accepted Answer

The lac operon will be transcribed even when lactose is absent.

Question 8

Which molecule acts as the inducer in the lac operon system?

Accepted Answer

Allolactose

Question 9

What is the role of cAMP in the regulation of the lac operon?

Accepted Answer

It binds to CAP, allowing CAP to activate transcription of the lac operon.

Question 10

A bacterial cell is placed in an environment with high glucose and high lactose. What will happen to the transcription of the lac operon?

Accepted Answer

Transcription will be low due to inducer exclusion and low cAMP levels.

Question 11

Which of the following best describes positive control of gene expression?

Accepted Answer

An activator protein binds to DNA and increases the frequency of transcription initiation.

Question 12

Which of the following is a key advantage of post-translational control in bacteria?

Accepted Answer

It allows rapid response to environmental changes by modifying existing proteins.

Question 13

If the operator sequence of the lac operon is deleted, what is the most likely outcome?

Accepted Answer

The lac operon will be constitutively expressed, regardless of lactose presence.

Question 14

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

Accepted Answer

Low glucose, high lactose

Question 15

Which component of the lac operon encodes the enzyme that cleaves lactose into glucose and galactose?

Accepted Answer

lacZ

Question 16

A mutation in the promoter of the lac operon prevents RNA polymerase from binding. What is the result?

Accepted Answer

No transcription of the lac operon genes will occur.

Question 17

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

Accepted Answer

It is usually on but can be turned off when tryptophan is present.

Question 18

Which of the following is a similarity between the lac operon and the trp operon?

Accepted Answer

Both use a repressor protein to regulate transcription.

Question 19

Which of the following equations best represents the relationship between cAMP and glucose concentration in E. coli?

Accepted Answer

$$[	ext{cAMP}] \propto \frac{1}{[	ext{glucose}]}$$

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

Study Guide - Practice Questions