Question 1

Which of the following best describes the role of the SecA protein in the SecA-dependent general secretion pathway in bacteria?

Accepted Answer

SecA uses ATP hydrolysis to push unfolded proteins through the SecYEG translocon into the periplasm.

Question 2

A mutation in the gene encoding SecB would most likely result in which of the following cellular defects?

Accepted Answer

Accumulation of unfolded pre-secretion proteins in the cytoplasm.

Question 3

Which of the following is TRUE regarding the difference between repressors and activators in bacterial transcriptional regulation?

Accepted Answer

Repressors prevent transcription by binding to operator regions, while activators stimulate transcription by binding to regulatory sequences.

Question 4

In the lac operon, what is the effect of allolactose binding to the LacI repressor?

Accepted Answer

It causes the LacI repressor to release from the operator, allowing transcription of lacZYA.

Question 5

Which of the following best explains why Gram-negative bacteria have evolved multiple protein secretion systems (Type I–VII)?

Accepted Answer

To export proteins across both the inner and outer membranes, including toxins and digestive enzymes.

Question 6

A bacterium is exposed to high tryptophan levels. What is the expected effect on the trp operon?

Accepted Answer

The trp operon will be repressed by the TrpR-corepressor complex and transcription will be terminated by attenuation.

Question 7

Which of the following best describes the function of a sigma factor in bacterial transcription?

Accepted Answer

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

Question 8

In the two-component regulatory system, what is the role of the sensor kinase?

Accepted Answer

It detects environmental signals and autophosphorylates using ATP.

Question 9

Which of the following scenarios would most likely result in the expression of the arabinose operon (araBAD)?

Accepted Answer

Arabinose is present, causing AraC to bind to araI sites in a conformation that recruits RNA polymerase.

Question 10

Which of the following best describes the process of transcriptional attenuation in the trp operon?

Accepted Answer

It relies on the formation of alternative stem-loop structures in the leader mRNA, which can terminate or allow transcription based on tryptophan levels.

Question 11

A mutation that prevents the cleavage of the signal sequence from a periplasmic protein would most likely result in which outcome?

Accepted Answer

The protein remains anchored in the membrane and cannot fold properly in the periplasm.

Question 12

Which of the following equations correctly represents the hydrolysis of ATP during protein export by SecA?

Accepted Answer

$$ \mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i} $$

Question 13

Which of the following is a real-life example of posttranslational control in bacteria?

Accepted Answer

The use of anti-sigma factors to inhibit sigma factor activity until needed.

Question 14

Which of the following best explains why bacteria use alternative sigma factors?

Accepted Answer

To coordinate the expression of different sets of genes (regulons) in response to environmental changes.

Question 15

Which of the following is the correct sequence of events for the export of a periplasmic protein via the Sec pathway?

Accepted Answer

Translation completes, SecB binds the protein, SecA pushes it through SecYEG, LepB cleaves the signal sequence.

Question 16

Which of the following best describes a regulon?

Accepted Answer

A set of genes or operons controlled by a single regulatory protein.

Question 17

In the context of the lac operon, which equation best represents the induction of gene expression by allolactose?

Accepted Answer

$$ 	ext{LacI} + 	ext{allolactose} ightarrow 	ext{LacI-allolactose complex (inactive repressor)} $$

Protein Export and Regulation of Gene Expression in Bacteria

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