Question 1

Which of the following best defines a gene according to modern molecular biology?

Accepted Answer

A region of DNA that can be expressed to produce a final functional product, either a polypeptide or an RNA molecule.

Question 2

During transcription in bacteria, which DNA strand is used as the template, and in what direction is RNA synthesized?

Accepted Answer

The 3' to 5' strand is used as template; RNA is synthesized 5' to 3'.

Question 3

Which of the following statements about the lac operon is CORRECT?

Accepted Answer

The lac operon is transcribed as a single mRNA that encodes multiple proteins.

Question 4

What is the role of the sigma (σ) factor in bacterial transcription?

Accepted Answer

It recognizes specific promoter sequences and directs RNA polymerase to initiate transcription.

Question 5

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

Accepted Answer

A repressor protein binds to the operator, preventing transcription.

Question 6

In the context of the lac operon, what is the effect of high glucose and high lactose concentrations?

Accepted Answer

Low cAMP levels, CRP does not bind, and only weak transcription occurs.

Question 7

Which of the following is a key feature of housekeeping genes?

Accepted Answer

They are under constitutive expression and are essential in all cells.

Question 8

What is the function of the Shine-Dalgarno sequence in bacterial mRNA?

Accepted Answer

It serves as a ribosome-binding site for initiation of translation.

Question 9

Which of the following scenarios will result in the highest level of lac operon transcription?

Accepted Answer

Low glucose, high lactose

Question 10

A mutation in the –10 region of a bacterial promoter is most likely to:

Accepted Answer

Reduce the affinity of RNA polymerase for the promoter, decreasing transcription.

Question 11

Which molecule acts as the true inducer of the lac operon?

Accepted Answer

Allolactose

Question 12

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

Accepted Answer

It binds to CRP (CAP), allowing it to activate transcription when glucose is low.

Question 13

Which of the following best describes an operon?

Accepted Answer

A cluster of genes under the control of a single promoter and transcribed as a single mRNA.

Question 14

In blue/white screening for recombinant plasmids, what is the expected result for a colony containing a recombinant plasmid?

Accepted Answer

The colony will be white due to disruption of the lacZ α fragment.

Question 15

Which of the following is TRUE regarding the use of IPTG in blue/white screening?

Accepted Answer

IPTG induces the lac operon by inactivating the LacI repressor but is not metabolized by the cell.

Question 16

Which of the following best explains why E. coli prefers glucose over lactose as a carbon source?

Accepted Answer

High glucose inhibits adenylate cyclase, lowering cAMP and preventing CRP activation of the lac operon.

Question 17

Which of the following is a direct consequence of a mutation that inactivates the lacI gene?

Accepted Answer

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

Question 18

Which of the following best describes the mechanism by which heat shock induces new gene expression in E. coli?

Accepted Answer

RNA polymerase replaces σ70 with σ32, directing transcription to heat shock gene promoters.

Question 19

Which of the following is NOT a function of the lacZ gene product?

Accepted Answer

Transport of lactose into the cell.

Regulation of Gene Expression in Prokaryotes: Biochemistry Study Notes

Study Guide - Practice Questions