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Example Questions
Example Question #1 : Regulating Transcription
Which statement about transcription is false?
Normally, proteins which activate histone acetyl-transferase have an inhibitory role in transcription
A promoter is typically upstream of the gene for which it initiates transcription
Corepressor proteins can play an inhibitory role in gene expression even without directly binding to DNA
Multiple proteins are required to interact in regulating eukaryotic gene RNA transcription
None of the other statements is false
Normally, proteins which activate histone acetyl-transferase have an inhibitory role in transcription
Among the proteins needed for RNA transcription are RNA polymerase, activators, and repressors. Corepressor proteins indeed bind to repressors, rather than DNA, in order to inhibit gene expression. Promoters are located toward the 5’ region of the sense strand (i.e., upstream). Normally, however, histone acetylation increases, rather than inhibits, gene expression (and hence transcription), by removing positive charges on the histone, thus decreasing the attractive interaction between the positively charged histones and negatively charged DNA. The decreased attraction allows room for transcription factors and RNA polymerase to bind promoter regions, increasing the incidence of transcription.
Example Question #1 : Regulating Transcription
Which of the following is true about transcriptional regulation?
None of these
The 3’ end of pre-RNA is capped, while the 5’ end of pre-RNA is modified by poly-A tails
Spliceosomes splice DNA
The 3’ untranslated region is where protein kinases attach, regulating different intra and extra-cellular signaling pathways
None of these
Untranslated regions never yield proteins, and thus do not attach to protein kinases. The 5’ end of pre-RNA is capped, and the 3’ end modified by poly A tails. Pre-RNA is, indeed, spliced when introns are removed. This is performed by spliceosomes, which only splice RNA, not DNA.
Example Question #2 : Regulating Transcription
Which of the following is true regarding bacterial transcription?
It involves addition of methyl cap at the end of transcription
It occurs in the same location as eukaryotic transcription
It is immediately followed by translation
It utilizes reverse transcriptase
It is immediately followed by translation
Transcription is the process of utilizing information in DNA molecules to make RNA molecules. It can occur in eukaryotes (such as humans) and in prokaryotes (such as bacteria). In eukaryotic transcription, the DNA is transcribed to RNA inside the nucleus. Upon completion, the synthesized RNA undergoes further post-transcriptional modifications such as addition of methyl cap, poly-A tail, and removal of introns. After these modifications, the RNA molecule leaves the nucleus, enters the cytoplasm, and undergoes translation (process of synthesizing proteins).
In contrast, bacterial transcription occurs in the cytoplasm and does not involve any of the post-transcriptional modifications. As a result, the transcribed RNA can immediately be used to synthesize proteins; therefore, translation immediately follows transcription in bacteria.
Recall that reverse transcriptase is a special enzyme that converts RNA to DNA (‘reverse’ of transcription). It is found in some viruses such as HIV.
Example Question #72 : Anabolic Pathways And Synthesis
During which of the following phase(s) of the cell cycle does transcription occur?
G1 phase
More than one of these are true
S phase
G2 phase
More than one of these are true
Transcription is the process of transcribing RNA molecules from DNA. This is a normal cellular process that is required for cells to grow and function properly (because these RNA molecules are eventually converted to proteins, the building blocks of cells). Growth of cells occurs in G1 and G2 phases; therefore, transcription occurs during both of these phases.
Note that DNA replication occurs during S phase; therefore, no DNA molecules will be available for transcription during S phase and transcription will be halted.
Example Question #5 : Regulating Transcription
A bacteria is known to have a defect in a protein that codes for the sigma factor. What will you most likely observe in this bacteria?
Complete halt of DNA replication and transcription because there is an increased degradation of both DNA and RNA polymerase
Complete halt of transcription because there is an increased degradation of RNA polymerase
Complete halt of transcription because RNA polymerase stays as a holoenzyme
Increased post-transcriptional modifications
Complete halt of transcription because RNA polymerase stays as a holoenzyme
Sigma factor is a special molecule in bacteria that is used to initiate transcription. In a bacterial cell, RNA polymerase is typically kept in its inactive form, called holoenzyme. When it is needed for transcription, RNA polymerase is converted to its active form by sigma factor. Sigma factor facilitates the binding of RNA polymerase to the gene sequence on the corresponding DNA molecule. Upon binding, RNA polymerase will carry out transcription and generate a new mRNA strand.
Example Question #73 : Anabolic Pathways And Synthesis
Promoter regions on DNA templates bind RNA polyermase and determine where transcription will begin. Which of the following could be part of a promoter region in bacteria?
3' - CTAGCGTAGCAGCA - 5'
3' - TTCGTAGCATAACG - 5'
5' - CGCTATAATGCT - 3'
5' - TACGTGCGAATAG - 3'
5' - CCGGTTAACCGG - 3'
5' - CGCTATAATGCT - 3'
A Pribnow box is a type of promoter region in bacteria that contains a sequence similar to the eukaryotic TATA box. 5'- TATAAT -3' will be found in the Pribnow box and signifies that the particular section of DNA is a promoter region. The eukaryotic TATA box typically contains the sequence 5'- TATAAA -3' and also serves as a promoter region, typically found upstream of a gene.
Example Question #74 : Anabolic Pathways And Synthesis
Genetic variety is accomplished in eukaryotes via which of the following mechanisms?
I. Pieces of DNA can move around spontaneously within the genome
II. Multiple, distinct proteins can be translated from a single coding region of mRNA
III. Segments of DNA can spontaneously switch to become new DNA coding regions
I, II, and III
II and III
I and III
I only
I and II
I, II, and III
Transposable elements are those that can move around within the genome, which increases genetic diversity. Also, due to alternative splicing of introns, multiple distinct proteins can be synthesized from the same exact mRNA transcript. One example of this is antibody production. Segments of DNA can spontaneously switch to become new DNA coding regions (mutation). This also increases genetic diversity, if this occurs in the germ-line cells.
Example Question #1 : Regulating Transcription
Inhibition of RNA polymerase II would disrupt which of the following processes?
Synthesis of DNA
Synthesis of tRNA
Synthesis of rRNA
Synthesis of mRNA
Synthesis of protein
Synthesis of mRNA
RNA polymerase II is the polymerase that catalyzes the synthesis of mRNA from a coding strand of DNA. Therefore, mRNA synthesis would be greatly affected by an inhibition of RNA polymerase II.
Example Question #9 : Regulating Transcription
How does the action of histone acetyltransferases affect transcription?
It increases the rate of transcription by adding positive charge to histones
It decreases the rate of transcription by removing positive charge from histones
It decreases the rate of transcription by adding positive charge to histones
It increases the rate of transcription by removing positive charge from histones
It increases the rate of transcription by removing positive charge from histones
For this question, we need to consider how histone acetyltransferases affect histones. Then, we need to determine how these modified histones affects the expression of genes.
First, it's important to note that histones are proteins that mostly contain positive charges. As a result of this, histones are able to associate with DNA very well, since DNA contains a negatively charged backbone. When histones associate with DNA in this way, the DNA molecule becomes tightly coiled around the histones. In this tightly bound conformation, the collection of DNA and proteins are referred to as hererochromatin. What's more is that when the DNA is tightly bound like this, the transcription machinery in the cell is physically blocked from associating with genes. Thus, gene expression is lowered.
Histone acetyltransferases are enzymes that attach acetyl groups to the positively charged lysine residues that are part of histones. Remember, the positive charge of these lysine residues is what allows the histones to associate with the DNA. When acetyl groups are added, the positive charge on these histones becomes neutralized. As a result, the histones are no longer able to associate with the DNA. What this means is that the transcription machinery in the cell is now able to physically access the genes, allowing gene expression to increase.
Example Question #2 : Regulating Transcription
An inhibition of RNA polymerase III would directly affect which of the following processes?
Synthesis of mRNA
Synthesis of protein
Synthesis of DNA
Synthesis of tRNA
Synthesis of rRNA
Synthesis of tRNA
RNA polymerase III catalyzes the synthesis of tRNA - RNA that is responsible for carrying amino acids during translation. So, synthesis of protein will be affected down the line, however the direct effect of an inhibition of RNA polymerase III would be the inability to create tRNA.
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