Question 1

Which of the following best describes the role of sigma factors in prokaryotic transcription initiation?

Accepted Answer

Sigma factors confer promoter specificity to the RNA polymerase holoenzyme.

Question 2

During heat shock in bacteria, which sigma factor becomes predominant and what is its effect?

Accepted Answer

Sigma $$\$$sigma^{32}$$; increases expression of heat-shock genes.

Question 3

Which step in prokaryotic transcription is almost always the rate-limiting step and why?

Accepted Answer

Initiation, because it involves assembly of the apparatus and is subjected to regulatory mechanisms.

Question 4

What is the function of the closed complex during prokaryotic transcription initiation?

Accepted Answer

It involves duplex DNA interacting with the sigma factor, keeping DNA in a closed (duplex) state.

Question 5

Which sequence is recognized by the sigma $$\$$sigma^{70}$$ factor at the -10 region of prokaryotic promoters?

Accepted Answer

TATAAT

Question 6

A mutation changes the -35 region of a bacterial promoter from TTGACA to CCGGANT. What is the most likely effect?

Accepted Answer

The promoter specificity will switch to sigma $$\$$sigma^{54}$$, altering gene expression.

Question 7

Which of the following is a feature of a strong intrinsic terminator in prokaryotes?

Accepted Answer

A region rich in G-C pairs forming a stem-loop followed by a U-rich region.

Question 8

What is the role of the Rho protein in prokaryotic transcription termination?

Accepted Answer

It acts as a helicase, unwinding the RNA-DNA hybrid and releasing the RNA.

Question 9

Which of the following statements about eukaryotic promoters is correct?

Accepted Answer

Eukaryotic promoters contain binding sites for many transcription factors and may include enhancers and silencers.

Question 10

Which RNA polymerase transcribes the majority of eukaryotic mRNAs?

Accepted Answer

RNA polymerase II

Question 11

What is the function of the TATA-binding protein (TBP) in eukaryotic transcription?

Accepted Answer

TBP binds to the TATA box, recruiting RNA polymerase to the promoter.

Question 12

Which of the following is true regarding the carboxy-terminal domain (CTD) of RNA polymerase II?

Accepted Answer

CTD consists of 52 repeats of the sequence YSPTSPS and is subject to multiple phosphorylation events.

Question 13

Which event marks the transition from transcription initiation to elongation in eukaryotes?

Accepted Answer

Phosphorylation of the CTD tail of RNA polymerase II by TFIIH.

Question 14

A researcher deletes the upstream enhancer region of a gene. What is the most likely effect on transcription?

Accepted Answer

Transcription will decrease due to loss of activator binding sites.

Question 15

Which of the following best explains why abortive initiation occurs during transcription?

Accepted Answer

RNA polymerase is stuck at the promoter, repeatedly synthesizing and releasing short RNA chains until it escapes.

Question 16

Which of the following is a key difference between prokaryotic and eukaryotic transcription termination?

Accepted Answer

Prokaryotes use a terminator sequence that forms a hairpin loop, while eukaryotes use a cleavage signal (AAUAAA) followed by polyadenylation.

Question 17

Which formula correctly represents the consensus sequence for the eukaryotic TATA box?

Accepted Answer

$$	ext{TATA(A/T)A(A/T)}$$

Question 18

A mutation in the CTD of RNA polymerase II prevents its phosphorylation. What is the most likely consequence?

Accepted Answer

Transcription initiation will occur, but elongation will be impaired.

Question 19

Which of the following statements about enhancers is correct?

Accepted Answer

Enhancers can be located far from the promoter and increase transcription by providing additional binding sites for transcription factors.

Question 20

Which general transcription factor is required for both DNA helicase activity and phosphorylation of RNA polymerase II during eukaryotic transcription initiation?

Accepted Answer

TFIIH

Prokaryotic and Eukaryotic Transcription: Mechanisms and Regulation

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