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Homeostasis and Gene Expression
Homeostasis and Gene Expression
Driving Question:
Driving Question:
How does C. elegans maintain normal internal conditions as the environment changes?
How does C. elegans maintain normal internal conditions as the environment changes?
By the end of this lesson, we hope that you will be able to:
By the end of this lesson, we hope that you will be able to:
- Make accurate 48-hour observations of the worms in different environments, and compare their activity to your 15-minute and 24-hour observations.
- Analyze and interpret data from the scientific literature.
- Develop an explanation for how differences in gene expression help C. elegans maintain homeostasis.
Homeostasis: maintaining balance
Homeostasis: maintaining balance
Homeostasis allows organisms and cells to maintain constant conditions even as the environment changes.
Homeostasis allows organisms and cells to maintain constant conditions even as the environment changes.
Your body is constantly performing a balancing act that allows you to remain alive and functional as external conditions change. Whether the outside temperature is 10° or 100° F, your body uses feedback mechanisms to maintain the same internal temperature. Every time you shiver or sweat, homeostasis is in action.
When wild type C. elegans were moved to a high salt environment, water left the cells of the worm. Homeostasis was disrupted and the worms appeared dead or severely impacted. After 24 hours, however, the worms appear to recover.
Let's see if they maintain homeostasis and recover after 48 hours.
Worm Observations - 48 hours after chunking
Worm Observations - 48 hours after chunking
Watch the videos and fill out the third row of your observation data table.
Wild type on LOW salt
Wild type on LOW salt
Wild type on HIGH salt
Wild type on HIGH salt
Mutant worms on LOW salt
Mutant worms on LOW salt
Mutant worms on HIGH salt
Mutant worms on HIGH salt
Developing an Explanation
Developing an Explanation
After 48 hours in the new high salt environment, we see that the wild type worms have somehow recovered. They are moving, eating, and reproducing.
How did they recover?
Below are 4 graphs that show experimental data from scientists who thought that glycerol might be involved in keeping worms from shrinking in high salt, based on similar experiments in yeast. Which graphs can support your explanation for why you think the wild type worms recovered after a change to a high salt environment?
Graph A
Graph A
Glycerol content of wild type and mutant worms in low salt
Data from this figure were originally published in PLoS Genetics in 2011.
Graph B
Graph B
Glycerol content of wild type worms grown on low and medium salt for 18 hours
Data from this figure originally published in the American Journal of Physiology - Cell Physiology in 2004
Graph C
Graph C
Glycerol accumulation over time in wild type worms grown on medium salt
Data from this figure originally published in the American Journal of Physiology - Cell Physiology in 2004
Graph D
Graph D
Accumulation of Glycerolase in wild type and mutant worms grown on low or medium salt for 18 hours.
Glycerolase is the enzyme that carries out the final step in making glycerol inside worm cells. It is coded for by the gpd gene.
Data from this figure were originally published in PLoS Genetics in 2011
Take the quiz below to see how well you interpret the data.
Take the quiz below to see how well you interpret the data.
(Keep this webpage open to see the study the graphs well.)
Maintaining Balance through Gene Expression
Maintaining Balance through Gene Expression
Gene Expression
Gene Expression
Remember this picture? Graph D shows the amount of glycerolase produced by the wild type and mutant worms in the two salt concentrations.
The wild type worms are able to ramp up production of glycerol when challenged by the high salt environment by producing more of the glycerolase enzyme. The mutant worms have a much lower increase in glycerolase production because they are always producing more glycerol and there is less need to ramp up glycerol production when moved to a high salt environment.
The level of glycerolase enzyme in the worm is controlled by the amount of mRNA made from the gpd gene in the DNA. Information from a gene (gpd) being used to make a product (the enzyme glycerolase) is called gene expression. Which type of worm shows heightened gene expression when the worm is moved from a low salt to a higher salt environment?
The Wild Type worm shows increased gene expression when moved to a higher salt environment, as is shown by increased glycerol production.
Which is better?
Which is better?
Do the wild type worms have an advantage by ramping up glycerol production when exposed to a new environment? Or do the mutants have an advantage by constantly producing high levels of glycerol even when it is not needed?
There is probably a trade-off, one strain may be favored over the other depending on the environmental conditions.
For wild type worms, the advantage of only making glycerol when needed is that it takes energy to make glycerol. This slows down the worms’ growth and development when ramping up glycerol production. The wild type worms are bigger, more active, and reproduce more quickly than the mutant worms in a low salt environment. In their "normal" (low salt) environment, wild type worms would be able to out compete the mutant worms.
For mutant worms, the advantage to making high glycerol all the time is that then the organism is prepared if it suddenly encounters an environment with high osmotic stress like high salt.
Lesson 4 Comprehension Questions
Lesson 4 Comprehension Questions
A. Why you think the wild type worms recovered after a change to a high salt environment?
B. Choose the data from one of the graphs and use it to support your explanation.
C. Which type of worm shows heightened expression of the gpd gene when the worm is moved from a low salt to a higher salt environment?
Next Step: Go to Lesson 5
Next Step: Go to Lesson 5
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