- I can describe an example of how genetic engineering is used in research.
- I can use a photograph to get and present data.
This information is not for classroom content, but rather to prepare teachers for the photographs and activities and potential questions from students. Additional information is in the background information provided thus far.
One of the genes that is most commonly transferred into organisms—from bacteria to mammals—is green fluorescent protein (GFP). GFP occurs naturally in the jellyfish Aequorea victoria. GFP protein is fluorescent: it absorbs light at one wavelength and emits it at another. (This is different from bioluminescence, such as light from fireflies, which is generated by a chemical reaction by specific enzymes and substrates.) GFP absorbs blue light and emits green light. GFP photographs are taken with camera filters, so only the emitted green light is seen. GFP fluorescence can be so strong, however, that a test tube of purified GFP glows faintly green in natural light.
Begin the Activity
- Graph paper
Explain to students:
- Cells are hard to see. Illustrations of cells in textbooks are brightly colored, but real cells are transparent. To see cells under a microscope, scientists usually stain them. For example, pathologists stain tissue biopsies to be able to see if cells are abnormal or normal. Staining kills cells, however, and makes them expand or shrink. GFP allows researchers to see living cells by using a special fluorescence microscope.
- GFP is a naturally fluorescent protein. The gene originally comes from fluorescent jellyfish. Scientists use GFP as a “reporter” protein: it “reports” on the location, size, movement, or metabolism of cells. Transferring the GFP gene into cells makes them fluorescent so scientists can observe them in their natural, living state. Scientists use GFP to track the growth of neurons, organ development in embryos, and the spread of cancer cells. In 2008, scientists who developed use of GFP as a reporter won in the Nobel Prize for medicine.
- In this activity, GFP is used to measure myotubes, which are developing muscle fibers. The photographs were taken with a fluorescence microscope by scientists who are studying the effect of myostatin, the protein whose gene is mutated in British Blue cows and in people with the hypertrophied muscles. Myostatin inhibits muscle development. That is why when the gene for it is mutated and less myostatin or defective myostatin is made, extra muscle is produced.
Give students handouts of the photos. In pairs or small groups, have students measure the width in millimeters of as many cells as possible from the photos of GFP cells, and then calculate an average width for each cell type. Ask students to make a bar graph of their results.
Note that students will need to make decisions about how many cells to measure and where to measure. They’ll need to consider and report on the precision of their measurements based on their equipment. Assure them that all scientists deal with these issues.
Graph features should include width in millimeters on the Y axis and cell types on the X axis, labels for both X and Y axes, a Y axis that begins at 0 and has correctly spaced unit marks, and a title and a legend that explains graph features.
Questions to Consider
Q: What conclusions can you draw from your measurements and graphs?
A: Genetically modifying myotube cells with the GFP gene made it easier to see, photograph, and measure the cells. Without the GFP gene, researchers would have to kill, process, and stain the myotubes, which might change their shape and size.
Normally, myostatin balances myotube growth. Normal myotubes are smaller than myotubes that are altered or treated to block the myostatin pathway. The scientists who did this experiment saw about a four-fold difference in diameter between myotubes with and without myostatin. Myostatin slows and controls muscle growth.
Q: What is the connection between your results and the appearance of people or animals who make less myostatin than usual.
A: Myostatin restricts muscle growth, so animals or people with certain mutations in myostatin have extra muscles.
Q: What medical or commercial implications might these findings about myostatin have?
A: People with muscle-wasting diseases, such as muscular dystrophy, might benefit from therapy to block myostatin, which might grow their muscles. Athletes might want to use the same therapy for a competitive advantage.
Q: What issues came up in your data collection that you would report if you were writing about this experiment?
A: See notes about deciding how many cells to measure, where to measure, etc.
Q: If you could genetically modify any organism, what would you modify and why? How might you do it?
A: Students might think of applications in agriculture, arts, or science. This could be a starting point for a writing assignment or presentation, investigating whether anyone has tried that application before and, if so, what the results were.
- Case study analysis: Choose a GMO case study, either: 1) herbicide-resistant corn (maize), 2) insect-resistant corn (maize), 3) golden rice, or 4) NewLeaf potatoes. Investigate and write about, or give a presentation, on how and why the plant was genetically modified. Describe advantages and disadvantages to society of the GMO plant.
- Writing activity: Write persuasively about whether myostatin inhibitors should be allowed in amateur or professional sports.
- Cross-disciplinary writing activity: Investigate and write about how growing crops that are selectively bred or genetically modified affects biodiversity. Describe what scientists and farmers are doing to preserve biodiversity; for example, creating seed banks, preserving habitats, or encouraging diversity in agriculture.
For research purposes, scientists have made directed mutations in GFP to alter the color of light it emits. Genes for other fluorescent proteins have also been isolated, creating a spectrum of fluorescent proteins available for research. This means that individual living cells can be distinguished by their different colors, even when they are in a mass of cells—such as the mouse brain cells. The color spectrum of fluorescent proteins with the wavelengths of light emitted by each protein could be the basis of a cross-disciplinary lesson with physical sciences.