Question 1

Which of the following best describes the role of the sigma (σ) factor in prokaryotic transcription initiation?

Accepted Answer

It recognizes and binds to the –35 and –10 promoter regions, positioning RNA polymerase for transcription initiation.

Question 2

A mutation changes the –10 (Pribnow box) sequence from 5′–TATAAT–3′ to 5′–TATGGT–3′ in a bacterial promoter. What is the most likely effect on transcription?

Accepted Answer

Transcription initiation will be less efficient because the promoter is less easily recognized and unwound.

Question 3

During prokaryotic transcription, which DNA strand serves as the template for RNA synthesis, and in what direction is the RNA synthesized?

Accepted Answer

The template strand; RNA is synthesized 5′ → 3′

Question 4

Which of the following sequences is most likely to be found at the +1 transcription start site in a prokaryotic gene?

Accepted Answer

A sequence located 5–9 bases downstream of the –10 box

Question 5

What is the primary mechanism by which rho-independent (intrinsic) termination occurs in prokaryotic transcription?

Accepted Answer

A hairpin loop forms in the RNA followed by a string of U’s, causing RNA polymerase to dissociate.

Question 6

If the coding strand of a gene is 5′–ATGCGTACG–3′, what is the sequence of the mRNA transcribed from this gene?

Accepted Answer

5′–AUGCGUACG–3′

Question 7

Which of the following best explains why the –10 region (Pribnow box) is A/T-rich in prokaryotic promoters?

Accepted Answer

A/T base pairs are easier to unwind due to fewer hydrogen bonds, facilitating open complex formation.

Question 8

A bacterial gene has the following promoter region: 5′–TTGACA–17bp–TATAAT–3′. If the spacing between the –35 and –10 boxes is increased to 25 bp, what is the most likely outcome?

Accepted Answer

Transcription initiation will be less efficient because optimal spacing is disrupted.

Question 9

Which of the following events occurs during the elongation phase of prokaryotic transcription?

Accepted Answer

RNA polymerase synthesizes RNA in the 5′ → 3′ direction, and the transcription bubble moves downstream.

Question 10

Which of the following best describes the difference between rho-dependent and rho-independent termination in prokaryotes?

Accepted Answer

Rho-dependent termination requires a protein factor, while rho-independent relies on RNA secondary structure and weak A–U base pairing.

Question 11

A researcher identifies a DNA sequence with the following features: a –35 box (TTGACA), a –10 box (TATAAT), and a downstream region with inverted repeats followed by a poly-A stretch. What is the most likely function of the downstream region?

Accepted Answer

It acts as a rho-independent transcription terminator.

Question 12

Which of the following equations correctly represents the directionality of RNA synthesis during transcription?

Accepted Answer

$$5' \rightarrow 3'$$

Question 13

In a prokaryotic cell, what would be the immediate consequence if the sigma factor was nonfunctional?

Accepted Answer

RNA polymerase would not efficiently recognize or bind to promoter regions, reducing transcription initiation.

Question 14

Which of the following statements about the central dogma is correct?

Accepted Answer

Information flows from DNA to RNA to protein.

Question 15

A mutation in the rut site of a gene prevents rho protein binding. What is the most likely effect on transcription?

Accepted Answer

Rho-dependent termination will fail, and transcription may continue past the normal stop site.

Question 16

Which of the following best describes the relationship between the coding strand of DNA and the mRNA produced during transcription?

Accepted Answer

The mRNA is identical to the coding strand except that U replaces T.

Question 17

Which of the following is NOT a feature of prokaryotic gene structure?

Accepted Answer

A polyadenylation signal for mRNA processing

Question 18

During which stage of prokaryotic transcription does the sigma factor dissociate from RNA polymerase?

Accepted Answer

Elongation

Question 19

A prokaryotic gene has a strong promoter. Which of the following features is most likely present?

Accepted Answer

A –10 box sequence closely matching 5′–TATAAT–3′ and optimal spacing between –35 and –10 boxes

Transcription in Prokaryotes: Mechanisms and Gene Structure

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