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Example Questions
Example Question #75 : Anabolic Pathways And Synthesis
During which of the following phase(s) of the cell cycle does transcription occur?
S phase
G2 phase
G1 phase
More than one of these are true
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 transcription because RNA polymerase stays as a holoenzyme
Increased post-transcriptional modifications
Complete halt of transcription because there is an increased degradation of RNA polymerase
Complete halt of DNA replication and transcription because there is an increased degradation of both DNA and RNA polymerase
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 #76 : 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' - TTCGTAGCATAACG - 5'
5' - CCGGTTAACCGG - 3'
5' - TACGTGCGAATAG - 3'
3' - CTAGCGTAGCAGCA - 5'
5' - CGCTATAATGCT - 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 #77 : 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
I and II
I and III
II and III
I only
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 #81 : Anabolic Pathways And Synthesis
Inhibition of RNA polymerase II would disrupt which of the following processes?
Synthesis of mRNA
Synthesis of protein
Synthesis of rRNA
Synthesis of DNA
Synthesis of tRNA
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 #7 : Regulating Transcription
How does the action of histone acetyltransferases affect transcription?
It decreases the rate of transcription by adding positive charge to histones
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 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 #82 : Anabolic Pathways And Synthesis
An inhibition of RNA polymerase III would directly affect which of the following processes?
Synthesis of DNA
Synthesis of mRNA
Synthesis of rRNA
Synthesis of protein
Synthesis of tRNA
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.
Example Question #51 : Nucleic Acid Synthesis
How does RNA polymerase know when to end transcription of a gene?
It reaches an uncodeable segment of the DNA
It reaches the Hogness box
It reaches the TATA box
It reaches a poly A tail
It synthesizes a termination sequence
It synthesizes a termination sequence
RNA polymerase travels down DNA beginning at the promoter site (could be TATA box or Hogness box in eukaryotes). It reads the DNA and synthesizes mRNA along the way, until it reaches a point where it reads the DNA and synthesizes a termination sequence. This notifies the RNA polymerase that it should end transcription of the gene.
Example Question #52 : Nucleic Acid Synthesis
Spliceosomes must be able to recognize where to splice mRNA so that introns are correctly cut out. What sequence is nearly always conserved in introns to ensure proper splicing?
None of these
(Splice) GU-------pyrimidine--AG (splice)
(Splice) AG-----------purines--GU (splice)
(Splice) GU----------purines--AG (splice)
(Splice) AG----------pyrimidines--GU (splice)
(Splice) GU-------pyrimidine--AG (splice)
Spliceosomes recognize the conserved sequence, GU, and splice just before those two nucleotides. They then continue onwards and when they recognize a pyrimidine followed by the nucleotides, AG, they splice again immediately after the AG. This is almost always conserved in introns to ensure proper splicing.
Example Question #53 : Nucleic Acid Synthesis
Which of the following is/are true regarding prokaryotic RNA polymerases?
I. RNA polymerase requires the sigma protein factor to initiate transcription.
II. Prokaryotes have multiple types of RNA polymerase.
III. RNA polymerase requires the rho protein factor to terminate transcription.
IV. Sigma protein is not required for RNA polymerase to initiate transcription in prokaryotes.
I and IV
I, II, and III
I and II
I and III
II, III, and IV
I and III
There are few differences between prokaryotes and eukaryotes in what concerns transcription. In prokaryotes there is only one RNA polymerase, while in eukaryotes there are three: I , II and III. In prokaryotes, both sigma factor and rho factor are required for transcription to occur, but not in eukaryotes.
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