Question 1

Which of the following best describes the function of constitutive genes in bacterial cells?

Accepted Answer

They are expressed continuously and are essential for basic cellular functions.

Question 2

What is the primary mechanism by which allosteric regulation alters enzyme activity?

Accepted Answer

Effector molecules bind to a non-catalytic (allosteric) site, causing a conformational change.

Question 3

Which posttranslational modification is most likely to change the activity of an enzyme by adding a phosphate group?

Accepted Answer

Phosphorylation

Question 4

In the regulation of the lac operon, what happens when both lactose and glucose are present?

Accepted Answer

Transcription is inhibited due to lack of CAP activation, even though the lac repressor is inactive.

Question 5

Which equation correctly represents the conversion of ATP to cAMP by adenyl cyclase?

Accepted Answer

$$\mathrm{ATP} \rightarrow \mathrm{cAMP} + \mathrm{PP_i}$$

Question 6

Which of the following best describes negative transcriptional control?

Accepted Answer

A repressor protein binds to DNA and inhibits transcription initiation.

Question 7

What is the effect of increasing the number of AMP groups attached to glutamine synthetase, as shown in the diagram?

Accepted Answer

Enzyme activity decreases as more AMP groups are added.

Question 8

Which scenario best illustrates feedback inhibition in a biosynthetic pathway?

Accepted Answer

The end product binds to the allosteric site of the first enzyme, inhibiting its activity.

Question 9

Which of the following is true about inducible genes such as those encoding β-galactosidase?

Accepted Answer

They are expressed only when their substrate (inducer) is available.

Question 10

Which regulatory system allows bacteria to preferentially use glucose over other carbon sources, resulting in diauxic growth?

Accepted Answer

Catabolite repression

Question 11

What is the role of the CAP protein in the regulation of the lac operon?

Accepted Answer

CAP must be bound to the CAP site to promote RNA polymerase binding and transcription initiation.

Question 12

Which of the following best describes the effect of glucose on cAMP levels in E. coli?

Accepted Answer

Low glucose increases cAMP levels.

Question 13

Which equation represents the group translocation process for glucose uptake in bacteria?

Accepted Answer

$$\mathrm{PEP} + \mathrm{Glucose} \rightarrow \mathrm{Pyruvate} + \mathrm{Glucose{-}P}$$

Question 14

Which of the following is a major difference between negative and positive transcriptional control?

Accepted Answer

Negative control inhibits transcription, while positive control promotes transcription.

Question 15

Which term describes a network of operons under control of a common global regulatory protein, but with individual operons controlled separately by their own regulators?

Accepted Answer

Modulon

Question 16

Which sigma factor in E. coli is primarily responsible for the expression of genes during stationary phase?

Accepted Answer

$$\$$sigma^{S}$$

Question 17

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

Accepted Answer

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

Question 18

Which of the following best explains why biosynthetic enzymes are not synthesized when the end product of the pathway is present?

Accepted Answer

The end product acts as a corepressor, inhibiting transcription of biosynthetic enzymes.

Question 19

Which of the following is an example of a housekeeping gene?

Accepted Answer

Gene encoding ribosomal RNA

Question 20

Which of the following best describes the effect of an inducer on an inactive activator protein in positive transcriptional control?

Accepted Answer

The inducer binds to the activator, converting it to its active form and promoting transcription.

Gene Regulation in Microorganisms: Mechanisms and Examples

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