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Experience 2:
Is That DNA in My Food?
| You will need... |
Time:
Materials:
Per class: |
One class period 50 minutes |
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hot plate |
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600mL beaker |
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beaker tongs or glove |
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300mL of water |
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thermometer |
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several balances |
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liquid dishwashing detergent |
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dry wheat plant (from hobby or flower store) |
| Per group: |
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1 gram of raw wheat germ |
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test tube |
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test tube stopper |
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100mL graduated cylinder |
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1mL pipette |
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15mL of ice-cold rubbing alcohol |
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2 wooden sticks |
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Extraction of DNA handout |
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safety glasses (one pair/student) |
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paper towel |
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| Teacher Preparation: |
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Pour 300mL of water into a 600mL beaker. |
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Place the beaker of water on a hot plate. |
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Turn the hot plate on low. |
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Heat the water to 50 - 60°C. |
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Procedures:
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Show students a wheat plant and ask them what they think it is. Have them create a list of foods that they have eaten this week that contain wheat. |
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Remind students that wheat is a plant, a living thing with cells and DNA. So yes, there is DNA in our food! |
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Instruct students to extract wheat germ DNA by following the directions on the Extraction of DNA handout |
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Help students to understand that the DNA they have extracted came from the wheat germ. They also need to understand that they broke open billions of cells and extracted the DNA from all of those cells. The reason the DNA glob is visible to the naked eye is because of the amount of DNA involved. This is not just one or two strands, but the strands that were in each of the billions of cells that we opened. |
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Discuss with students what the scientists in a biotechnology lab might do with the DNA once it is extracted. Extraction of DNA is just the first process in genetic engineering. |
 Wheat germ is the embryo of the wheat seed. This part of the seed contains many nutrients. Lots of foods are made with wheat: breads, pastas and cereals - and anything made with flour. Things made from whole wheat contain the wheat germ, whereas things made only from white flour don't contain wheat germ.
See Website for more information on wheat germ.
DNA Extraction - How it Works:
The DNA in raw wheat germ is located in the nucleus of the cell. We must first get to the DNA before we can extract it. Each step of the procedure plays an important part. |
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The warm water softens the cell and nuclear membranes so that they can be opened to get to the DNA. The water temperature is also important because at 50 - 60° Celsius it denatures the enzymes that would cut the DNA in fragments. If the DNA were cut into fragments, it would be too short to be visible. At 80° Celsius the DNA itself would denature and then we would not be able to do the activity. |
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The detergent pulls the fatty lipid membranes that surround the cell and nucleus apart to release the DNA. It works much like dishwashing soap that cuts through the fatty grease when you wash dishes. |
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The DNA is floating around in the solution and cannot be seen. Cold alcohol precipitates it out of solution so it can be seen. |
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Gene Transfer
Once scientists have extracted the DNA they then have to purify it. After that is done, the gene of interest has to be isolated. They use special enzymes that work like scissors to cut that gene out from the rest of the DNA. There are several different methods used to transport the gene into the plant cell. One method is to use Agro bacterium, a type of  bacteria that injects part of its DNA into plants. Scientists replace part of the bacterium's DNA with the desired gene. It then becomes a "gene shuttle," transporting the desired gene into the plant cell. Once inside the cell, the gene can join the DNA of the plant. The plant cells are treated with chemicals that cause them to start growing into whole new plants. This is a special property of plants; most animal cells cannot regenerate this way. When they get big enough, the young plants are transferred to soil. Eventually the plants with the gene of interest are crossed with commercial varieties of the plant. Many plants with the gene must be created so they can be studied. After about six years of experiments, the government decides if a genetically modified plant will be safe to eat and safe for the environment. Farmers then plant seeds of genetically modified plants, and harvest them at the end of the growing season. See the museum's Website and the resources area for animations on this process.
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Assessment:
Supervise students during the DNA extraction process. Monitor students' safety precautions, ability to follow directions, ability to work as partners, ability to measure and use scientific equipment and check to see if they successfully extracted DNA. |
