1 markA length of DNA is used to transcribe a segment of RNA called mRNA. This happens during the process of transcription within the nucleus of a cell.
Which of the following shows the correctly transcribed RNA from the length of DNA shown below.
A-G-G-T-C-C-A-T-G-T-A-A-A
A-G-G-U-C-C-A-U-G-U-A-A-A
A-G-G-T-C-C-A-T-G-T-A-A-A
U-C-C-A-G-G-U-A-C-A-U-U-U
T-C-C-A-G-G-T-A-C-A-T-T-T
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1 markThere are several different types of RNA. Which of the following is not a type of RNA?
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1 markDNA replication occurs through specific steps.
The steps below are out of sequence:
Topoisomerase relaxes supercoiling in front of the replication fork.
Ligase joins the fragments on the lagging strand.
Helicase unwinds the DNA strands.
DNA polymerase synthesizes new strands of DNA continuously on the leading strand and discontinuously on the lagging strand.
Which of the following shows the correct sequence for the DNA replication process?
1, 3, 4, 2
3, 1, 4, 2
1, 4, 2, 3
2, 3, 1, 4
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Transcription and translation are processes that occur in cells during the synthesis of new protein molecules.
Which of the following distinguishes between transcription and translation?
Translation occurs within the nucleus and involves converting a sequence of nucleotides on a DNA strand into an mRNA strand; transcription occurs on a ribosome and involves using mRNA to form a polypeptide chain.
Transcription occurs within the nucleus and involves converting a sequence of nucleotides on an mRNA strand into a DNA strand; translation occurs on a ribosome and involves using DNA to form a polypeptide chain.
Transcription occurs within the nucleus and involves converting a sequence of nucleotides on a DNA strand into an mRNA strand; translation occurs on a ribosome and involves using mRNA to form a polypeptide chain.
Translation occurs within the nucleus and involves using mRNA to form a polypeptide chain; transcription occurs on a ribosome and involves converting a sequence of nucleotides on a DNA strand into an mRNA strand.
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Retroviruses are a group of viruses that infect host cells so that their DNA can be inserted into the host cell genome.
Which of the following describes what happens to a retrovirus's genetic material when retroviruses infect their host cells?
When retroviruses infect host cells their RNA needs to be converted into DNA before transcription and translation can occur.
When retroviruses infect host cells their DNA needs to be converted into RNA before transcription and translation can occur.
When retroviruses infect host cells their DNA needs to be converted into mRNA before transcription and translation can occur.
When retroviruses infect host cells their RNA needs to be converted into DNA after transcription and translation have occurred.
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1 markThe human TP53 gene encodes different forms of tumour suppressor protein. Which of the following best explains how different proteins can be made within different cell types from the one TP53 gene?
Different introns are selectively converted to exons.
Different exons are retained or spliced out of the primary transcript.
The GTP cap is selectively added to and activates different exons.
Different portions of the primary transcript remain bound to the template DNA.
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1 markResearchers were investigating the process of transcription in eukaryotic cells. They isolated pre-mRNA molecules from human fibroblast cells and analyzed their lengths using gel electrophoresis. The same mRNA sequences were then isolated from the cytoplasm and analyzed using electrophoresis to separate the sequences by size. The results are shown in Figure 1.
Which of the following conclusions about eukaryotic gene expression is best supported by the data in Figure 1?
Transcription occurs more efficiently in the cytoplasm than in the nucleus.
Translation occurs before RNA splicing in eukaryotic cells.
Post-transcriptional modification reduces the length of mRNA molecules.
Eukaryotic genes do not contain introns.
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1 markScientists are studying the role of a newly identified enzyme in the DNA replication process of eukaryotic cells. They propose that this enzyme is crucial for initiating DNA synthesis by assisting in unwinding the double helix during replication.
Which of the following questions would best guide the researchers towards a direct test of their proposal?
Does the inhibition of the enzyme prevent the unwinding of DNA at the replication fork?
Does the enzyme remain active throughout the G2 phase of the cell cycle?
How does the enzyme influence the repair of DNA after replication is completed?
Does the enzyme increase the speed of RNA transcription during replication?
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1 markIn an experiment to verify the nature of DNA replication, scientists used nitrogen isotopes to label the DNA of E. coli. The bacteria were grown in a medium containing heavy nitrogen (N15) and then switched to a medium containing light nitrogen (N14). The results after one round of replication are shown in the table below.
Round of Replication | % Heavy (N15) DNA | % Hybrid (Mixed N15/N14) DNA | % Light (N14) DNA |
|---|---|---|---|
0 | 100 | 0 | 0 |
1 | 0 | 100 | 0 |
2 | 0 | 50 | 50 |
Which of the following conclusions is best supported by this data?
DNA replication in E. coli is conservative.
DNA replication in E. coli is semi-conservative.
DNA replication in E. coli results in entirely new DNA after one round of replication.
DNA replication does not require nitrogen isotopes.
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1 markResearchers were investigating the role of RNA polymerase in transcription. They set up an in vitro transcription system with purified RNA polymerase, DNA template, and nucleotides. The researchers measured the rate of RNA synthesis under various conditions. The results are shown in Figure 1.
Which of the following conclusions about transcription is best supported by the data?
RNA polymerase can synthesize RNA without a DNA template.
Nucleotides are not necessary for RNA synthesis.
RNA polymerase is the primary enzyme responsible for RNA synthesis.
Heat does not affect the activity of RNA polymerase.
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The figure represents the process of expression of gene X in a eukaryotic cell.
The primary transcript in the figure is 15 kilobases (kb) long, but the mature mRNA is 7 kb in length. Describe the modification that most likely resulted in the 8 kb difference in length of the mature mRNA molecule. Identify in your response the location in the cell where the change occurs.
Predict the length of the mature gene X mRNA if the full-length gene is introduced and expressed in prokaryotic cells. Justify your prediction.
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Researchers are studying the use of RNA vaccines to protect individuals against certain diseases. To develop the vaccines, particular cells are first removed from an individual. Then mRNAs coding for specific proteins from a pathogen are introduced into the cells. The altered cells are injected back into the individual, where the cells make the proteins encoded by the introduced mRNAs. The individual then produces an immune response to the proteins that will help to protect the individual from developing a disease if exposed to the pathogen in the future.
When introduced into cells, the mRNAs used for vaccines must be stable so that they are not degraded before the encoded proteins are produced. Researchers developed several modified caps that they hypothesized might make the introduced mRNAs more stable than mRNAs with the normal GTP cap. To test the effect of the modified caps, the researchers produced mRNAs that differed only in their cap structure (no cap, the normal cap, or modified caps I, II, or Ill). They introduced the same amount of each mRNA to different groups of cells and measured the amount of time required for half of the mRNAs to degrade (mRNA half-life) and the total amount of protein translated from the mRNAs (Table 1).
TABLE 1. EFFECT OF mRNA CAP STRUCTURE ON mRNA HALF-LIFE AND PROTEIN TRANSLATED FROM THE INTRODUCED mRNA
5' Cap Structure | mRNA Half-Life ± | Total Amount of Protein |
No cap | 1.41 ± 0.02 | 0.011 ± 0.000 |
Normal GTP cap | 16.10 ± 1.83 | 1.000 ± 0.007 |
Modified cap I | 15.50 ± 1.57 | 4.777 ± 0.042 |
Modified cap II | 27.00 ± 2.85 | 13.094 ± 0.307 |
Modified cap III | 18.09 ± 0.81 | 6.570 ± 0.075 |
Based on the data, identify which cap structure is most likely to protect the end of the mRNAs from degradation.
Based on the data for the mRNAs with modified caps, describe the relationship between the mRNA half-life and the total amount of protein produced.
After examining the data on mRNA half-lives and the amount of protein produced, the researchers hypothesized that each mRNA molecule with modified cap I was translated more frequently than was each mRNA molecule with the normal GTP cap. Evaluate their hypothesis by comparing the data in Table 1.
The introduction of mRNAs into cells allows the cells to produce foreign proteins that they might not normally produce. Explain why the production of a foreign protein may be more likely from the introduction of mRNA than DNA into cells.
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1 markA scientist is investigating DNA replication in prokaryotes and introduces an enzyme inhibitor that prevents the formation of short DNA fragments, Okazaki fragments, on the lagging strand.
Which enzyme is most likely affected by this inhibitor?
Helicase
Topoisomerase
DNA Ligase
RNA Polymerase
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1 markScientists isolate bacterial DNA and introduce modified nucleotides that prevent strand elongation when incorporated into newly synthesized DNA strands. They observe that DNA synthesis is more disrupted on one strand than the other.
What explains why one strand is affected more than the other?
The leading strand is synthesized discontinuously, making it more susceptible to interruption.
The lagging strand is synthesized in short fragments, requiring repeated priming and joining of two DNA strands.
The leading strand requires RNA primers, which prevent elongation when replaced.
Modified nucleotides inhibit DNA polymerase so that new DNA strands are synthesised continuously on the leading strand and discontinuously on the lagging strand.
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1 markA team of molecular biologists investigates gene expression regulation in eukaryotic cells. They analyze the transcription rate of a specific gene under different conditions by measuring the amount of mRNA produced over time. Their findings are summarized in the table below:
Experimental condition | Relative mRNA levels (arbitrary units) |
|---|---|
Control (normal conditions) | 100 |
RNA polymerase inhibited | 5 |
Transcription factor mutated | 30 |
Histone acetylation increased | 150 |
Based on the data, which conclusion best explains the regulation of transcription in these cells?
Histone modifications primarily control transcription, as increased histone acetylation leads to a 50% rise in mRNA levels, demonstrating that the structure of DNA and histones is the main factor in regulating gene expression.
RNA polymerase is the sole determinant of transcription, as its inhibition reduces mRNA production by 95%, proving that no other factors significantly contribute to transcriptional regulation.
The transcription factor plays a critical role in gene expression, as its mutation results in a 70% reduction in mRNA levels, indicating that transcription factors are essential for transcriptional activation.
The 150% transcription rate observed with histone acetylation suggests that modifications of DNA and histones can be a more effective mechanism for increasing gene expression than transcription factor activation alone.
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1 markA polypeptide has the following amino acid sequence:
histidine - glutamine - lysine - alanine - valine - histidine - valine
The table below gives the tRNA anticodons for each amino acid.
Amino acid | tRNA anticodons |
|---|---|
histidine | CAU |
valine | GUA |
lysine | AAA |
alanine | GCU |
glutamine | CAG |
A mutation causes the 18th base in the DNA sequence to be deleted.
Which of the following would represent the amino acid sequence after this deletion?
histidine - glutamine - lysine - alanine - valine - histidine
histidine - glutamine - lysine - alanine - valine
histidine - glutamine - lysine - alanine - valine - glutamine
histidine - glutamine - lysine - alanine - valine - histidine - valine
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1 markA group of virologists is studying how retroviruses, such as HIV, survive inside human cells. Retroviruses are unique because their genomes are composed of RNA, yet they integrate their genetic material into the host cell’s DNA.
Which of the following processes involve both DNA and RNA in retroviruses?
I. Replication
II. Transcription
III. Translation
IV. Protein synthesis
I and II only
I, II, and IV only
II, III, and IV only
I, II, III, and IV
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(hours after introduction into cells)