Question 1

Which of the following best describes the role of the sigma subunit in bacterial transcription?

Accepted Answer

It recognizes and binds to the promoter region, enabling the RNA polymerase core enzyme to initiate transcription.

Question 2

A mutation in the -10 consensus sequence (Pribnow box) of a bacterial promoter would most likely result in:

Accepted Answer

Reduced or abolished transcription initiation at that promoter.

Question 3

Which of the following is true regarding the directionality of transcription in bacteria?

Accepted Answer

RNA is synthesized in the 5' to 3' direction using the template strand as a template.

Question 4

Which of the following equations correctly represents the formation of a phosphodiester bond during RNA synthesis?

Accepted Answer

$$\mathrm{NTP} + (RNA)_{n} \rightarrow (RNA)_{n+1} + PP_i$$

Question 5

Rifampicin is an antibiotic used to treat tuberculosis. Its mechanism of action is best described as:

Accepted Answer

Preventing the formation of the first phosphodiester bond by RNA polymerase during transcription initiation.

Question 6

Which of the following is NOT a feature of intrinsic (rho-independent) transcription termination in bacteria?

Accepted Answer

Requirement for the rho protein to catalyze transcript release.

Question 7

A bacterial gene is found to be transcribed only under heat shock conditions. Which sigma subunit is most likely involved in its transcription?

Accepted Answer

$$\$$sigma^{32}$$

Question 8

Which of the following best explains why the promoter region is not transcribed into RNA?

Accepted Answer

The promoter region is recognized and bound by RNA polymerase but transcription begins at the +1 nucleotide downstream of the promoter.

Question 9

Which of the following statements about the core enzyme of bacterial RNA polymerase is correct?

Accepted Answer

It requires the sigma subunit to recognize and bind to the promoter.

Question 10

A mutation in the rut sequence of a bacterial gene would most likely affect which process?

Accepted Answer

Rho-dependent termination.

Question 11

Which of the following best describes a consensus sequence?

Accepted Answer

A sequence of nucleotides that occurs most often at a particular position in related genes or species.

Question 12

During transcription elongation in bacteria, which of the following events occurs?

Accepted Answer

The core enzyme synthesizes RNA at a rate of approximately 40 nucleotides per second.

Question 13

Which of the following is a key difference between intrinsic and rho-dependent termination in bacteria?

Accepted Answer

Intrinsic termination requires a poly-U sequence, while rho-dependent termination does not.

Question 14

A researcher isolates a mutant E. coli strain that is resistant to rifampicin. Which of the following is the most likely explanation for this resistance?

Accepted Answer

A mutation in the RNA polymerase gene that prevents rifampicin binding.

Question 15

Which of the following best describes the function of alternative sigma subunits in bacteria?

Accepted Answer

They allow RNA polymerase to recognize different sets of promoters under varying environmental conditions.

Question 16

Which of the following sequences is most likely to be found at the -10 region (Pribnow box) of a typical E. coli promoter?

Accepted Answer

$$TATAAT$$

Question 17

Which of the following steps occurs first during the initiation of bacterial transcription?

Accepted Answer

The RNA polymerase holoenzyme binds loosely to the promoter to form the closed promoter complex.

Question 18

Which of the following is a plausible consequence if the stem-loop structure in intrinsic termination is not followed by a poly-U sequence?

Accepted Answer

The RNA polymerase may not be destabilized, leading to read-through transcription.

Question 19

Which of the following best explains why Rho-dependent termination may have evolved in bacteria?

Accepted Answer

To provide an additional layer of protection against invading phages.

The Biochemistry of RNA Synthesis and Transcription in Bacteria: Study Notes

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