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 conditions 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 transcription apparatus and is subject to regulation.

Question 4

What is the function of the Pribnow box in prokaryotic promoters?

Accepted Answer

It is the -10 consensus sequence recognized by sigma factors for transcription initiation.

Question 5

Which of the following is TRUE regarding the formation of the closed complex during prokaryotic transcription initiation?

Accepted Answer

Duplex DNA interacts with the sigma factor and remains closed; RNA polymerase binding is reversible.

Question 6

A mutation changes the -10 region of a bacterial promoter from TATAAT to TATGGT. What is the most likely effect?

Accepted Answer

Transcription initiation will be reduced due to decreased sigma factor binding.

Question 7

Which of the following best explains abortive initiation in prokaryotic transcription?

Accepted Answer

Short RNA chains are synthesized and released repeatedly before RNA polymerase escapes the promoter.

Question 8

In prokaryotes, what is the primary structural feature of a strong intrinsic terminator?

Accepted Answer

A G-C rich stem-loop structure followed by a U-rich region.

Question 9

Which protein is required for termination at weak terminators in prokaryotic transcription, and what is its mechanism?

Accepted Answer

Rho protein; it acts as a helicase to unwind the RNA-DNA hybrid and release the RNA.

Question 10

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 11

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

Accepted Answer

TBP binds to the TATA box and recruits RNA polymerase to the promoter.

Question 12

Which RNA polymerase transcribes all cellular mRNAs and most microRNAs in eukaryotes?

Accepted Answer

RNA polymerase II

Question 13

A researcher deletes an enhancer region located 10 kb upstream of a gene's TATA box. What is the most likely effect?

Accepted Answer

Transcription of the gene will decrease due to loss of activator binding.

Question 14

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

Accepted Answer

Eukaryotes use a polyadenylation signal (AAUAAA) for termination, while prokaryotes use terminator sequences.

Question 15

Which general transcription factor is NOT released from RNA polymerase II during elongation and is involved in both transcription initiation and DNA repair?

Accepted Answer

TFIIH

Question 16

The C-terminal domain (CTD) of RNA polymerase II contains repeats of which amino acid sequence?

Accepted Answer

$$YSPTSPS$$

Question 17

Which of the following best describes the function of insulators in eukaryotic gene regulation?

Accepted Answer

Insulators block the action of enhancers on promoters when placed between them.

Question 18

A mutation in the core promoter of a eukaryotic gene removes the TATA box but leaves the initiator sequence intact. What is the most likely outcome?

Accepted Answer

Transcription initiation may be reduced, but can still occur via the initiator sequence.

Question 19

Which of the following is TRUE about the assembly of the preinitiation complex (PIC) in eukaryotes?

Accepted Answer

TBP binds to the TATA box first, followed by the sequential recruitment of other general transcription factors.

Prokaryotic and Eukaryotic Transcription: Mechanisms and Regulation

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