Identify the RNA molecule that carries genetic information from the DNA to the ribosome.
Describe one structural difference between DNA and RNA.
Explain the role of RNA polymerase in transcription.
Predict what would happen to the resulting protein if RNA processing failed to remove introns.
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Identify the enzyme that adds nucleotides to a growing DNA strand during replication.
Describe the difference in DNA synthesis on the leading and lagging strands in DNA replication.
Explain why replication of DNA is known as semi-conservative
A summary of DNA replication is shown in the table below.
Table 1: Summary of the mechanisms involved in DNA replication
Mechanism |
|---|
a. RNA primers attach to the template strand to initiate DNA synthesis. |
b. Topoisomerase relaxes supercoiling in front of the replication fork. |
c. Helicase unwinds the DNA strands. |
d. DNA polymerase synthesizes new strands of DNA continuously on the leading strand and discontinuously on the lagging strand. |
e. Ligase joins the fragments on the lagging strand. |
Determine the correct order of the mechanisms that occur during DNA replication.
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Identify the organelle where translation occurs in eukaryotic cells.
Describe what happens to the mRNA before it leaves the nucleus during the process of transcription.
Explain how the sequence of nucleotides in mRNA determines the sequence of amino acids in a protein.
Predict the effect of a deletion of one nucleotide near the beginning of the coding region.
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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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A team of researchers is investigating how cells produce a particular protein that helps regulate growth in a species of freshwater fish. To better understand this process, the researchers examine the entire pathway from DNA replication through transcription and translation.
(i) Describe how complementary base pairing occurs during DNA replication.
(ii) Identify the enzyme responsible for joining DNA nucleotides.
To increase protein production, researchers design a version of the gene with a stronger promoter sequence.
(i) Explain the role of the promoter region in transcription.
(ii) Predict what would happen to transcription if the promoter sequence were deleted.
One version of the gene has a mutation that disrupts normal mRNA splicing.
(i) Describe what occurs during mRNA splicing.
(ii) Justify why incorrect splicing might lead to a nonfunctional protein.
To investigate how different versions of the growth-regulating protein are produced, the researchers examine the mRNA transcripts from the same gene in different tissues of the fish. They discover that the mRNA varies between tissues, even though the gene is identical.
(i) Describe two modifications made to the ends of the mRNA transcript before it leaves the nucleus.
(ii) Explain how alternative splicing allows different versions of a protein to be produced from the same gene.
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(hours after introduction into cells)