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About This Drill
AP Biology — Unit 6 — Gene Expression & Regulation — Drill 22 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
Practice interpreting transcription factor and gene regulation data with this AP Biology drill. You will analyze mRNA expression levels under four experimental conditions, identify the role of a transcription factor from loss-of-function data, explain basal versus activated expression, evaluate the mechanism of an inhibitor molecule from expression data, design an experiment to test whether a transcription factor contacts DNA directly, and predict evolutionary consequences of constitutive gene expression.
Passage
Researchers studying the regulation of a drought-response gene (DRG1) in the model plant Arabidopsis thaliana identified a transcription factor called TF-D that binds to the DRG1 promoter region. To characterize TF-D's role, the team measured DRG1 mRNA levels (in arbitrary units) under four experimental conditions. All experiments used equal amounts of leaf tissue, and mRNA was quantified by the same method. An activating protein (AP) that assists TF-D in binding the DRG1 promoter was also tested.
Observed DRG1 mRNA levels:
Condition 1 — Wild-type plant, activating protein (AP) present: mRNA = 850 units
Condition 2 — TF-D loss-of-function mutant, AP present: mRNA = 42 units
Condition 3 — Wild-type plant, AP absent: mRNA = 91 units
Condition 4 — Wild-type plant, AP present plus inhibitor molecule added: mRNA = 78 units
The inhibitor molecule was designed to block the interaction between TF-D and AP without directly binding to DNA.
Questions in This Drill
- Comparing Condition 1 to Condition 2, which of the following best describes the role of TF-D in regulating DRG1 expression?
- Comparing Condition 1 (wild-type plus AP: 850 units) to Condition 3 (wild-type, no AP: 91 units), which of the following best explains why DRG1 mRNA is still produced at a low level when AP is absent?
- Conditions 3 and 4 produce similar DRG1 mRNA levels (91 and 78 units, respectively), even though Condition 4 includes AP. The inhibitor molecule in Condition 4 blocks the interaction between TF-D and AP without binding to DNA. Which of the following best explains why Condition 4 mRNA levels resemble Condition 3 rather than Condition 1?
- A researcher wants to determine whether TF-D increases DRG1 transcription by directly binding the DRG1 promoter or by binding to another protein that in turn contacts the promoter. Which of the following experimental designs would most directly test whether TF-D physically contacts the DRG1 promoter DNA?
- DRG1 encodes a protein that helps the plant retain water during drought conditions. A spontaneous mutation increases TF-D activity, causing DRG1 to be expressed at high levels even when AP is absent and when the plant is not experiencing drought. Assuming the plant population lives in an environment with unpredictable rainfall, which of the following best predicts the long-term effect of this mutation on the fitness of individuals carrying it?