Question 1

Which of the following best defines a gene according to the modern understanding presented in the lecture?

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

What is the primary advantage for bacteria to organize genes of related function into an operon?

Accepted Answer

It allows for coordinated control of gene expression.

Question 3

In the trp operon, what is the role of tryptophan?

Accepted Answer

It acts as a corepressor that activates the repressor protein, shutting off transcription.

Question 4

Which of the following statements about repressible and inducible operons is correct?

Accepted Answer

A repressible operon is usually on and is turned off by a repressor-corepressor complex.

Question 5

A loss-of-function mutation in the lacI gene (encoding the Lac repressor) would most likely result in which phenotype?

Accepted Answer

The lac operon is transcribed constitutively, regardless of the presence or absence of lactose.

Question 6

Which molecule acts as the natural inducer of the lac operon in E. coli?

Accepted Answer

Allolactose

Question 7

What is the effect of high glucose levels on the transcription of the lac operon?

Accepted Answer

High glucose decreases cAMP levels, inactivating CRP and decreasing transcription.

Question 8

Which of the following best describes the role of CRP (cAMP receptor protein) in the regulation of the lac operon?

Accepted Answer

CRP acts as an activator that increases RNA polymerase affinity for the promoter when bound to cAMP.

Question 9

If both glucose and lactose are present in the environment, what is the expected state of the lac operon?

Accepted Answer

The lac operon is not transcribed because CRP is inactive and the repressor is not bound.

Question 10

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

Accepted Answer

Lactose present, glucose absent

Question 11

Which experimental result would indicate a mutation in the operator site of the lac operon?

Accepted Answer

The lac operon is transcribed constitutively, regardless of the presence or absence of lactose.

Question 12

Which of the following best explains why the lac operon is considered an 'AND gate' in logic terms?

Accepted Answer

It is expressed only when both lactose is present and glucose is absent.

Question 13

Which of the following is a direct product of the lacZ gene?

Accepted Answer

β-Galactosidase

Question 14

A loss-of-function mutation in the crp gene (encoding CRP) would most likely result in which phenotype?

Accepted Answer

The lac operon cannot be induced, even when lactose is present and glucose is absent.

Question 15

Which of the following best describes the molecular mechanism by which the LacI repressor recognizes the operator sequence?

Accepted Answer

It recognizes the specific shape and charge distribution of the operator DNA sequence via its amino acid sequence.

Question 16

Which of the following molecules is NOT hydrolyzed by β-galactosidase but can induce the lac operon in laboratory experiments?

Accepted Answer

IPTG

Question 17

Which of the following best describes feedback inhibition in the tryptophan biosynthesis pathway?

Accepted Answer

Tryptophan binds to the first enzyme in the pathway and inhibits its activity.

Question 18

Which of the following is true about the organization of genes in eukaryotes compared to prokaryotes?

Accepted Answer

Prokaryotes often organize genes of related function in operons for coordinated control.

Question 19

Which of the following best describes the role of X-gal in experiments with the lac operon?

Accepted Answer

It is a substrate that, when cleaved by β-galactosidase, produces a blue pigment.

Lecture 19 (unit 2)- Regulation of Gene Expression in Prokaryotes: Operons and Transcriptional Control

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