CHAPTER 15 REGULATION OF GENE EXPRESSION
Scientific Skills Exercise
Teaching objective: Students will analyze a figure that combines gene construct diagrams and a
bar graph showing gene expression for the control DNA sequence and three experimental DNA
constructs.
Teaching tips: A version of this Scientific Skills Exercise can be assigned in MasteringBiology.
There are two conceptual challenges in this exercise. The first is to interpret the relationship
between the different kinds of graphical data that are presented together in the figure. The gene
construct portion of the diagram shows schematics of control DNA segments that have the
specified deletion. (To conserve space, the large region between the promoter and the enhancer
region is omitted and indicated with slashes, as mentioned in the exercise.) These constructs are
spatially arranged on the y-axis to correspond to the other kind of graphical data: the horizontal
The second challenge is to understand the idea of a reporter gene, which can be difficult for
students. The cultured cells in which the experiment is done are cells that normally express the
mPGES-1 gene. This choice of cells is made to ensure that the cells have the necessary specific
transcription factors for expression of that gene. On the other hand, the fact that the cells are
expressing the mPGES-1 gene themselves would complicate the results if the constructs had the
mPGES-1 gene in them, under control of the various deletions. In this case, researchers would be
Students may wonder how this relates to the idea that each control element regulates a specific
gene and only that gene. In this experiment, researchers are altering the normal placement of
control elements. Normally, a group of control elements only regulates a given gene because
they are upstream of that gene at the appropriate distance for regulation of that gene to occur.
and blind: they regulate whatever gene is at the appropriate location downstream from them.
The illustrations of enhancers in the textbook (Figures 15.8, 15.10, and 15.11) focus on control
elements that act as activators. In this exercise, two of the control elements act as repressors of
Note that these data are the relative amount of gene expression, displayed as percentages relative
to the control, which is set at 100%. The actual level of reporter gene mRNA cannot be
determined from the graph.
Answers:
1. (a) The independent variable (the variable that was manipulated by the researchers) was the
identity of the DNA element that was deleted from the experimental DNA constructs. (b) The
4. (a) Yes; deletion of control element #1 or #2 led to an increase in gene expression relative to
the control DNA. The cells with DNA that lacked control element #1 produced about 180% of
Suggested Answers for End-of-Chapter Essay Questions
See the general information on grading short-answer essays and the suggested rubric at the
beginning of this document.
8. Scientific Inquiry
You could use the cloned gene to synthesize a labeled probe and carry out in situ hybridization
9. Focus on Evolution
The highly conserved regions may code for sequences that help regulate gene expression (such
as proximal or distal control elements, including groups of elements in enhancers) using
10. Focus on Interactions
Sample key points:
To survive, bacterial cells must efficiently use the available resources.
They can synthesize most of the compounds they need, but when a needed compound is
available in their environment, they can stop synthesizing it.
There are two mechanisms for this feedback regulation:
Sample top-scoring answer:
To survive and reproduce, a bacterial cell must efficiently use the cellular resources that are
available. Bacterial cells can synthesize most of the compounds they need, such as amino acids,
11. Synthesize Your Knowledge
The lux genes are likely to be grouped in an operon, under the control of a single promoter and
operator, so that the genes are all turned on at the same time (or all turned off at the same time).