Q: Which sequence signals the site for polyadenylation in eukaryotic pre-mRNA, and what is the function of the polyA tail?

The consensus sequence $$\text{AAUAAA}$$; the polyA tail increases mRNA stability and aids in translation.

Question 1

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

Accepted Answer

It recognizes and binds to the -35 and -10 promoter sequences, enabling RNA polymerase to initiate transcription at the correct site.

Question 2

A mutation changes the -10 sequence of a bacterial promoter from $$	ext{TATAAT} to$$ $$	ext{TATGGT}. $$What is the most likely effect on transcription of the associated gene?

Accepted Answer

Transcription will initiate at a lower rate due to decreased promoter recognition by the sigma factor.

Question 3

Which of the following statements correctly distinguishes between rho-dependent and rho-independent termination in bacteria?

Accepted Answer

Rho-dependent termination requires the rho protein to bind to the rut site on RNA and catch up to RNA polymerase, while rho-independent termination relies on a stem-loop structure followed by a uracil-rich sequence to destabilize the RNA-DNA hybrid.

Question 4

In eukaryotic cells, which RNA polymerase is responsible for transcribing all protein-coding genes?

Accepted Answer

RNA polymerase II

Question 5

A researcher isolates a eukaryotic mRNA and finds that it lacks a 7-methylguanosine cap at its 5-prime end. Which of the following processes is most likely to be impaired in this mRNA?

Accepted Answer

Export of the mRNA from the nucleus

Question 6

Which of the following best explains why eukaryotic transcription and translation are not coupled, unlike in bacteria?

Accepted Answer

Eukaryotic mRNAs are translated in the cytoplasm, while transcription occurs in the nucleus, requiring mRNA processing and export.

Question 7

Which sequence signals the site for polyadenylation in eukaryotic pre-mRNA, and what is the function of the polyA tail?

Accepted Answer

The consensus sequence $$	ext{AAUAAA}$$; the polyA tail increases mRNA stability and aids in translation.

Question 8

A mutation in the gene encoding the U1 snRNP would most directly affect which process?

Accepted Answer

Recognition of the 5-prime splice site during pre-mRNA splicing

Question 9

Which of the following is a key difference between the core promoter of bacterial and eukaryotic protein-coding genes?

Accepted Answer

Bacterial promoters contain -35 and -10 consensus sequences, while eukaryotic core promoters often contain a TATA box and a transcriptional start site.

Question 10

Which of the following best describes the function of the mediator complex in eukaryotic transcription?

Accepted Answer

It mediates the effects of regulatory transcription factors on RNA polymerase II and is required for the transition from initiation to elongation.

Question 11

A eukaryotic gene contains several introns and exons. Which of the following mechanisms allows a single gene to produce multiple different polypeptides?

Accepted Answer

Alternative splicing, which generates mature mRNAs with different combinations of exons.

Question 12

Which of the following is true regarding self-splicing introns?

Accepted Answer

The RNA molecule itself acts as a ribozyme to catalyze intron removal.

Question 13

A patient is found to have a mutation that prevents the addition of the CCA sequence to the 3-prime end of tRNA molecules. What is the most likely consequence?

Accepted Answer

The tRNAs will not be able to bind amino acids, impairing translation.

Question 14

Which of the following best describes the role of the 2-prime OH group of an adenosine within the intron during Group II and spliceosomal splicing?

Accepted Answer

It attacks the 5-prime splice site, initiating cleavage and forming a lariat structure.

Question 15

Which of the following is a function of the 7-methylguanosine cap on eukaryotic mRNA?

Accepted Answer

It is recognized by cap-binding proteins that facilitate mRNA export, translation initiation, and splicing.

Question 16

A scientist observes that a eukaryotic pre-mRNA is not being properly spliced in a mutant cell line. Further analysis reveals that the branch site adenosine is mutated. What is the most likely effect?

Accepted Answer

The 5-prime splice site will not be recognized, and the intron will not be removed.

Question 17

Which of the following best describes the torpedo model of transcription termination for RNA polymerase II?

Accepted Answer

An exonuclease degrades the RNA downstream of the cleavage site, catching up to RNA polymerase II and causing its dissociation from DNA.

Question 18

Which of the following modifications is most commonly found in both prokaryotic and eukaryotic tRNAs?

Accepted Answer

Base modification, such as methylation of cytosine.

Question 19

A gene is transcribed in two different cell types, but the mature mRNA contains different exons in each cell type. Which regulatory mechanism is most likely responsible for this observation?

Accepted Answer

Cell-type specific splicing factors that act as repressors or enhancers to regulate alternative splicing.

Gene Transcription and RNA Modification: Study Notes

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