Question 1

Which of the following best describes a constitutively expressed gene in bacteria?

Accepted Answer

A gene that is always 'ON' and expressed regardless of environmental conditions.

Question 2

In the lac operon, what is the function of the lacY gene product?

Accepted Answer

It encodes for permease, which facilitates the entry of lactose into the cell.

Question 3

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It allows for the coordinated expression of multiple genes from a single mRNA transcript in bacteria.

Question 4

A mutation in the operator region of the lac operon prevents the repressor from binding. What is the most likely outcome?

Accepted Answer

The lac operon will be constitutively expressed, even in the absence of lactose.

Question 5

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

Accepted Answer

It encodes a repressor protein that regulates transcription of the lac operon.

Question 6

Which of the following is an example of a cis-acting element in gene regulation?

Accepted Answer

The operator sequence located upstream of the structural genes.

Question 7

What happens to the lac operon when both glucose and lactose are present in the environment?

Accepted Answer

The lac operon is repressed due to catabolite repression by glucose.

Question 8

Which enzyme is responsible for breaking down lactose into glucose and galactose in E. coli?

Accepted Answer

β-galactosidase

Question 9

If a bacterial cell is placed in an environment with only lactose (no glucose), what will happen to the lac operon?

Accepted Answer

The lac operon will be induced and transcribed.

Question 10

Which of the following best describes negative control of gene expression in bacteria?

Accepted Answer

Binding of a regulatory protein inhibits transcription.

Question 11

Which of the following equations best represents the central dogma of molecular genetics?

Accepted Answer

$$DNA \rightarrow RNA \rightarrow Protein$$

Question 12

A mutation in the lacI gene results in a nonfunctional repressor protein. What is the expected effect on the lac operon?

Accepted Answer

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

Question 13

Which of the following is a real-life example of a gene that is expressed constitutively in bacteria?

Accepted Answer

The gene encoding RNA polymerase

Question 14

Which of the following best describes the function of an inducer in an inducible operon system?

Accepted Answer

It binds to the repressor, causing it to release from the operator and allowing transcription.

Question 15

Which of the following is true about the structure of lactose?

Accepted Answer

It is a disaccharide composed of glucose and galactose.

Question 16

Which of the following scenarios would most likely result in the highest level of lac operon expression?

Accepted Answer

No glucose, high lactose

Question 17

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

Accepted Answer

It is the site where the repressor protein binds to regulate transcription.

Question 18

Which of the following is an example of a trans-acting element in gene regulation?

Accepted Answer

The repressor protein encoded by the lacI gene

Question 19

Which of the following best explains why polycistronic mRNA is advantageous for bacteria?

Accepted Answer

It allows for the simultaneous regulation and expression of multiple functionally related genes.

Question 20

Which of the following is the correct sequence of events when lactose is present in the environment of E. coli?

Accepted Answer

Lactose binds to the repressor, causing it to release from the operator, allowing RNA polymerase to transcribe the operon.

Regulation of Gene Expression in Bacteria: The lac Operon Model

Study Guide - Practice Questions