Q: Which equation correctly represents the conversion of lactose to glucose and galactose by $$eta-$$galactosidase?

$$\mathrm{Lactose} \xrightarrow{\beta\text{-galactosidase}} \mathrm{Glucose} + \mathrm{Galactose}$$

Q: A partial diploid E. coli (merozygote) has the genotype $$lacI^+ lacZ^- / lacI^- lacZ^+. $$What will be the phenotype regarding $$eta-$$galactosidase production in the presence of lactose?

$$eta-$$galactosidase is produced only when lactose is present.

Question 1

Which of the following best describes the central dogma of molecular genetics?

Accepted Answer

Genetic information flows from DNA to RNA to protein.

Question 2

In the lac operon, which gene encodes the enzyme responsible for breaking down lactose into glucose and galactose?

Accepted Answer

lacZ

Question 3

Which of the following is a cis-acting element in the lac operon?

Accepted Answer

The operator region (lacO)

Question 4

A mutation in the lacO operator that prevents repressor binding will result in which phenotype?

Accepted Answer

The operon is constitutively on, regardless of lactose presence.

Question 5

Which equation correctly represents the conversion of lactose to glucose and galactose by $$eta-$$galactosidase?

Accepted Answer

$$\mathrm{Lactose} \xrightarrow{\beta	ext{-galactosidase}} \mathrm{Glucose} + \mathrm{Galactose}$$

Question 6

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

Accepted Answer

It enhances transcription by facilitating RNA polymerase binding to the promoter.

Question 7

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

Accepted Answer

Low glucose, high lactose

Question 8

A partial diploid E. coli (merozygote) has the genotype $$lacI^+ lacZ^- / lacI^- lacZ^+. $$What will be the phenotype regarding $$eta-$$galactosidase production in the presence of lactose?

Accepted Answer

$$eta-$$galactosidase is produced only when lactose is present.

Question 9

Which of the following best explains catabolite repression in the lac operon?

Accepted Answer

Glucose inhibits the formation of cAMP, preventing CAP from binding and activating transcription.

Question 10

In the trp operon, what is the effect of high tryptophan levels on gene expression?

Accepted Answer

Transcription of trp structural genes is repressed.

Question 11

Which mechanism allows the trp operon to fine-tune gene expression in response to tryptophan levels?

Accepted Answer

Attenuation via formation of alternative mRNA secondary structures

Question 12

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

Accepted Answer

The lacI repressor protein

Question 13

A mutation in the lacI gene that produces a superrepressor (cannot bind lactose) will result in which phenotype?

Accepted Answer

The operon is always off, regardless of lactose presence.

Question 14

Which of the following best describes the function of riboswitches in bacterial gene regulation?

Accepted Answer

They are mRNA segments that bind small molecules and alter gene expression.

Question 15

Which equation correctly represents the relationship between cAMP concentration and glucose levels in E. coli?

Accepted Answer

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

Question 16

Which of the following is true about polycistronic mRNA in prokaryotes?

Accepted Answer

It encodes multiple proteins from a single mRNA transcript.

Question 17

Which of the following is a real-world example of a repressible operon system?

Accepted Answer

The trp operon in E. coli

Question 18

A mutation in the trp operator that prevents repressor binding will result in which phenotype?

Accepted Answer

The trp operon is constitutively on, regardless of tryptophan levels.

Question 19

Which of the following best explains the difference between inducible and repressible operon systems?

Accepted Answer

Inducible systems are activated by the presence of a substrate, while repressible systems are inhibited by the presence of an end product.

Regulation of Gene Expression in Bacteria: The lac Operon and Beyond

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