RNA, Transcription, And Translation Flashcards
In eukaryotes, which RNA polymerase makes rRNA?
Possible Answers:
RNA polymerase II
RNA polymerase I
RNA polymerase IV
RNA polymerase III
RNA polymerase I
Explanation:
The RNA polymerases are numbered in the order that their products are used in protein synthesis.
RNA polymerase I makes ribosomal rRNA in eukaryotes.
RNA polymerase II makes messenger mRNA in eukaryotes.
RNA polymerase III makes transfer tRNA in eukaryotes.
Which of the following subunits of RNA polymerase is solely required for initiation of transcription?
Possible Answers:
σ (sigma)
β (beta)
ω (omega)
α (alpha)
σ (sigma)
Explanation:
The sigma factor is solely required for the initiation of transcription. In fact, the sigma subunit will often fall off of the enzyme during the elongation phase of transcription. Binding of the sigma factor is an important signal for transcription to begin.
The other subunits are crucial to the elongation and termination phases.
Which of the following codons is the mRNA start codon that initiates translation?
Possible Answers:
UAG
UGA
AUG
UAA
AUG
Explanation:
The codon AUG initiates translation in both eukaryotes and prokaryotes. Interaction with this codon by a tRNA molecule allows a methionine residue to enter the ribosome and serve as the starting point for amino acid elongation.
UGA, UAA, and UAG are mRNA stop codons and stop protein synthesis by causing the ribosomal subunits to dissociate and release the polypeptide.
Which of the following best describes the key function of helicases during transcription?
Possible Answers:
Catalyzing the interaction between transcription factors and the DNA strand.
Relief of tension in the DNA strands to prevent breakage.
Separation of two strands of DNA; “unwinding” gives polymerases access to the strand.
Re-annealing of two DNA strands once transcription and translation processes are complete.
Cleaving methyl groups from an unwound DNA strand.
Separation of two strands of DNA; “unwinding” gives polymerases access to the strand.
Explanation:
Helicases are required for separating two DNA strands so that the rest of transcription can take place. Polymerases work on single strands of DNA, thus the bonds holding the double strands together must be removed.
Transcription factors that are the first to bind DNA in heterochromatin regions, often promote euchromatin formation, and recruit other transcriptional machinery to promote transcription are best known as which of the following?
Possible Answers:
DNA Polymerases
RNA holoenzyme
Pioneer factors
Histone demethyltransferases
Co-factors
Pioneer factors
Explanation:
The correct answer is pioneer factors. Pioneer factors are able to bind DNA in condensed regions and promote euchromatin formation by recruitment of histone demethyltransferases and acteyltransfereses to modify proximal histones. Additionally, these pioneer factors recruit other transcription factors and co-factors to promote transcription. DNA polymerases are involved with DNA replication, not transcription. The RNA holoenzyme is a protein complex consisting of RNA polymerase, transcription factors, and regulator proteins that binds promoters and catalyzes transcription.
Before RNA polymerase can initiate transcription, this protein must bind to it, creating the RNA polymerase holoenzyme and allowing for the initiation of transcription.
Possible Answers:
Activator protein
Helicase
Topoisomerase
Beta factor
Sigma factor
Sigma factor
Explanation:
RNA polymerase cannot initiate transcription by itself. It binds to the promoter but must wait for a sigma factor to bind to it. Now the RNA polymerase holoenzyme can proceed with transcription.
Which of the following is not dependent on the C-terminal domain (CTD) of RNA polymerase II?
Possible Answers:
Polyadenylation
Transcription termination
mRNA splicing
None of the other answers
5’ capping
None of the other answers
Explanation:
The correct answer is none of the other answers. Only mRNA transcribed by polymerase II undergo 5’ capping, polyadenylation, and splicing. The C-terminal domain of this polymerase serves as a binding site and docking platform for many of the enzymes that initiate these processes. Moreover, experiments in which the CTD is truncated show that mRNA transcripts are not capped, polyadenylated, and spliced.
Which polymerase is involved in transcribing ribosomal RNA (except 5S rRNA)?
Possible Answers:
RNA polymerase I
DNA polymerase V
DNA polymerase IV
RNA polymerase II
RNA polymerase III
RNA polymerase I
Explanation:
The correct answer is RNA polymerase I. The sole purpose of RNA polymerase I in eukaryotes is to transcribe ribosomal RNA, with the exception of 5S rRNA, which is transcribed by RNA polymerase III. RNA polymerase III also transcribes tRNAs and other small RNAs. Transcripts of RNA polymerase II are 5’ capped, polyadenylated, and spliced to ultimately be translated into functional protein. DNA polymerase IV/V are polymerases involved in DNA replication and repair.
What is the role of the promoter region in the regulation of gene expression?
Possible Answers:
Allow for alternative splicing and recombination of genetic components
Bind negative regulators to inhibit gene expression
Alter gene expression by binding transcription factors
Recruit RNA polymerase and transcription factors to DNA
Recruit RNA polymerase and transcription factors to DNA
Explanation:
The promoter region is the site of a gene where RNA polymerase and other transcription factors bind to DNA, upstream from the gene locus. A mutation in this region commonly results in a decrease in the amount of gene transcribed.
An enhancer region is a stretch of DNA that alters gene expression by binding transcription factors, while a silencer region is a site on the gene where repressor proteins bind. Introns are intervening non-coding segments of DNA that are not expressed in the final protein. Alternative splicing patterns of introns and exons allows for multiple proteins to be generated from a single gene.
Which of the following are methods for termination of transcription in prokaryotes?
I. Release factor binding
II. Rho-mediated termination
III. Hairpin loop (stem loop) formation
Possible Answers:
III only
II and III
I, II, and III
I only
II and III
Explanation:
The binding of release factors is a common way to terminate translation, not transcription.
Rho-mediated termination and hairpin loop formation are both common ways to terminate prokaryotic transcription. The formation of the hairpin loop disrupts the transcription machinery and the DNA-RNA interactions, which allows termination of transcription. Rho is a protein that is capable of binding single-stranded RNA and terminating transcription.
What event is indicative of transcription initiation?
Possible Answers:
RNA polymerase is removed from the DNA
Telomerase lengthens the telomeres of the DNA
The RNA strand begins to be synthesized
RNA polymerase binds to the promoter
RNA polymerase binds to the promoter
Explanation:
During the initiation of transcription, RNA polymerase and a group of transcription factors bind to the promoter for a given gene. This DNA segment signals the RNA polymerase where to begin creating the RNA strand.
Which of the following best describes distant regulatory sequences that influence gene expression?
Possible Answers:
Transcriptional start sites
Promoters
Enhancers
Exons
Introns
Enhancers
Explanation:
The correct answer is enhancer. Transcription factors and mediators bind enhancer regions of DNA and influence the transcription of distant genes by chromatin looping to the proximal promoter. Promoters are regulatory sequences, however, they are typically 2 kilobase pairs upstream of the gene for which they influence transcription. Introns and exons make up a gene and are the non-coding and coding regions of the gene, respectively. The transcriptional start site consists of the first few nucleotides that are transcribed into an mRNA sequence from a gene, usually containing the 5’ untranslated region (UTR).
When does alternative splicing occur?
Possible Answers:
Following mRNA loading into ribosome
Following mRNA translocation to the cytosol
Following mRNA polyadenylation
Following pre-mRNA transcription in the nucleus
Following translation
Following pre-mRNA transcription in the nucleus
Explanation:
The correct answer is following pre-mRNA transcription in the nucleus. Pre-mRNA contains introns and exons. Following transcription, splicing and alternative splicing occurs to remove introns and select exons, respectively, by the spliceosome. Following splicing, 3’ poly adenylation and 5’ capping occur to generate a mature mRNA transcript that will translocate to the cytosol and be translated by ribosomes.
What element(s) do all eukaryotic promoter regions share?
Possible Answers:
A basal promoter (TATA box)
Enhancers that accept binding agents
None of these
Transcription factors
All of these
All of these
Explanation:
Eukaryotic promoters share basic, highly conserved structure. This area does not evolve quickly because it is extremely important in DNA transcription. These promoters (in most cases) include a basic basal promoter like a TATA box, and enhancers that bind to transcription factors.
During transcription of a eukaryotic cell, what determines the template strand?
Possible Answers:
The base sequence of the operator
The location of the AUG start codon
The base sequence of the promoter
The base sequence of the enhancer
The location of the MET start codon
The base sequence of the promoter
Explanation:
The TATA box is found in the promoter region of the template strand. This TATA box serves as a signal for the initiation of translation of DNA into mRNA. The location of the promoter region and it’s unique base sequence signals the start of the translation process.
