
Campbell Biology 11th Edition by Lisa Urry,Michael Cain,Steven Wasserman,Peter Minorsky,Jane Reece
Edition 11ISBN: 978-0134093413
Campbell Biology 11th Edition by Lisa Urry,Michael Cain,Steven Wasserman,Peter Minorsky,Jane Reece
Edition 11ISBN: 978-0134093413 Exercise 3
What Control Elements Regulate Expression of the mPGES-1
Gene The promoter of a gene includes the DNA immediately upstream of the transcription start site, but the control elements regulating the level of transcription of the gene (grouped in an enhancer.) may be thousands of base pairs upstream of the promoter. Because the distance and spacing of these control elements make them difficult to identify, scientists begin by deleting possible control elements and measuring the effect on gene expression. In this exercise, you will analyze data obtained from DNA deletion experiments that tested possible control elements for the human gene mPGES-1. This gene codes for an enzyme that synthesizes a type of prostaglandin, a chemical made during inflammation.
How the Experiment Was Done The researchers hypothesized that there were three possible control elements in an enhancer region located 8-9 kilobases upstream of the mPGES-1 gene. Control elements regulate whatever gene is in the appropriate downstream location. Thus, to test the activity of the possible elements, researchers first synthesized molecules of DNA ("constructs") that had the intact enhancer region upstream of a "reporter gene," a gene whose mRNA product could be easily measured experimentally. Next, they made three more DNA constructs with one of the three proposed control elements in deleted in each (see left side of figure). The researchers then introduced each DNA construct into a separate human cell culture, where the cells took up the DNA constructs. After 48 hours, the amount of reporter gene mRNA made by the cells was measured. Comparing these amounts allowed researchers to determine if any of the deletions had an effect on expression of the reporter gene, mimicking the effect that deletions would have had on mPGES-1 gene expression. (The mPGES-1 gene itself couldn't be used to measure expression levels because the cells express their own mPGES-1 gene. The mRNA from that gene would confuse the results.)
Data from the Experiment The diagrams on the left side of the figure show the intact DNA sequence (top) and the three experimental DNA constructs. A red X is located on the possible control element (1, 2, or 3) that was deleted in each experimental DNA construct. The area between the slashes represents the approximately 8 kilobases of DNA located between the promoter and the enhancer region. The horizontal bar graph on the right shows the amount of reporter gene mRNA that was present in each cell culture after 48 hours relative to the amount that was in the culture containing the intact enhancer region (top bar = 100%).
Interpret the Data
(a) What is the independent variable in the graph (b) What is the dependent variable (c) What was the control treatment in this experiment Label it on the diagram.
Gene The promoter of a gene includes the DNA immediately upstream of the transcription start site, but the control elements regulating the level of transcription of the gene (grouped in an enhancer.) may be thousands of base pairs upstream of the promoter. Because the distance and spacing of these control elements make them difficult to identify, scientists begin by deleting possible control elements and measuring the effect on gene expression. In this exercise, you will analyze data obtained from DNA deletion experiments that tested possible control elements for the human gene mPGES-1. This gene codes for an enzyme that synthesizes a type of prostaglandin, a chemical made during inflammation.
How the Experiment Was Done The researchers hypothesized that there were three possible control elements in an enhancer region located 8-9 kilobases upstream of the mPGES-1 gene. Control elements regulate whatever gene is in the appropriate downstream location. Thus, to test the activity of the possible elements, researchers first synthesized molecules of DNA ("constructs") that had the intact enhancer region upstream of a "reporter gene," a gene whose mRNA product could be easily measured experimentally. Next, they made three more DNA constructs with one of the three proposed control elements in deleted in each (see left side of figure). The researchers then introduced each DNA construct into a separate human cell culture, where the cells took up the DNA constructs. After 48 hours, the amount of reporter gene mRNA made by the cells was measured. Comparing these amounts allowed researchers to determine if any of the deletions had an effect on expression of the reporter gene, mimicking the effect that deletions would have had on mPGES-1 gene expression. (The mPGES-1 gene itself couldn't be used to measure expression levels because the cells express their own mPGES-1 gene. The mRNA from that gene would confuse the results.)
Data from the Experiment The diagrams on the left side of the figure show the intact DNA sequence (top) and the three experimental DNA constructs. A red X is located on the possible control element (1, 2, or 3) that was deleted in each experimental DNA construct. The area between the slashes represents the approximately 8 kilobases of DNA located between the promoter and the enhancer region. The horizontal bar graph on the right shows the amount of reporter gene mRNA that was present in each cell culture after 48 hours relative to the amount that was in the culture containing the intact enhancer region (top bar = 100%).

Interpret the Data
(a) What is the independent variable in the graph (b) What is the dependent variable (c) What was the control treatment in this experiment Label it on the diagram.
Explanation
(a)
The independent variable in the grap...
Campbell Biology 11th Edition by Lisa Urry,Michael Cain,Steven Wasserman,Peter Minorsky,Jane Reece
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