Question 1

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

Accepted Answer

Sigma factors are required for RNA polymerase to recognize and bind to specific promoter sequences, thereby determining which genes are transcribed.

Question 2

During heat shock in E. coli, which sigma factor becomes predominant and what is its primary function?

Accepted Answer

Sigma factor $$\$$sigma^{32}$$; it directs RNA polymerase to transcribe heat-shock genes.

Question 3

Which step in prokaryotic transcription is typically rate-limiting and subject to regulation?

Accepted Answer

Initiation, because assembly of the transcription apparatus determines whether transcription proceeds.

Question 4

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

Accepted Answer

It allows duplex DNA to interact with the sigma factor and core enzyme, with DNA remaining double-stranded.

Question 5

Which sequence is most commonly found at the -10 region of prokaryotic promoters and is crucial for transcription initiation?

Accepted Answer

TATAAT (Pribnow box)

Question 6

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

Accepted Answer

RNA polymerase repeatedly synthesizes and releases short RNA fragments before escaping the promoter and entering elongation.

Question 7

Which structural feature of a strong intrinsic terminator in prokaryotes is essential for termination of transcription?

Accepted Answer

A GC-rich stem-loop followed by a U-rich region in the RNA transcript.

Question 8

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

Accepted Answer

Rho acts as an RNA helicase that binds to the nascent RNA and unwinds the RNA-DNA hybrid, causing release of the RNA transcript.

Question 9

Which eukaryotic RNA polymerase is responsible for transcribing mRNA and some small RNAs such as microRNA?

Accepted Answer

RNA polymerase II

Question 10

In eukaryotic transcription, what is the function of the TATA-binding protein (TBP)?

Accepted Answer

TBP binds to the TATA box in the core promoter, causing DNA bending and facilitating recruitment of RNA polymerase.

Question 11

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

Accepted Answer

The CTD consists of multiple repeats of the sequence YSPTSPS and undergoes phosphorylation during transcription initiation and elongation.

Question 12

Which sequence acts as a signal for polyadenylation and transcription termination in eukaryotes?

Accepted Answer

AAUAAA

Question 13

Which of the following statements about enhancers is CORRECT?

Accepted Answer

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

Question 14

Which of the following best describes the difference between prokaryotic and eukaryotic transcription termination?

Accepted Answer

Prokaryotes use intrinsic terminators or Rho-dependent termination, while eukaryotes rely on a polyadenylation signal and cleavage downstream of the coding region.

Question 15

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

Accepted Answer

Transcription initiation will be reduced because the sigma factor will bind less efficiently.

Question 16

Which general transcription factor in eukaryotes is responsible for both DNA helicase and kinase activities during transcription initiation?

Accepted Answer

TFIIH

Question 17

Which of the following is a function of insulator elements in eukaryotic genomes?

Accepted Answer

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

Question 18

Which equation best represents the separation between the -35 and -10 regions in a typical prokaryotic promoter?

Accepted Answer

$$13 	ext{ to } 19 	ext{ bp}$$

Question 19

Which of the following is TRUE regarding the assembly of the preinitiation complex (PIC) in eukaryotic transcription?

Accepted Answer

PIC assembly is an ordered process involving TBP/TAFs binding to the TATA box, followed by recruitment of other general transcription factors and RNA polymerase II.

Prokaryotic and Eukaryotic Transcription: Mechanisms and Regulation

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