Name: ______Period: ______
Facilitator: ______Materialist: ______
Reporter: ______Recorder: ______
DNA Extraction Lab:
Strawberry, Wheat Germ, and Bananas Oh My!
Background
All living things contain genetic material. DNA is a genetic material that controls the every cell’s activities and appearance and is also the material that is passed on to the progeny (offspring). Many bacterial cells contain only one main chromosome. Many of the common multicellular (many celled) organisms you encounter have body cells that are diploid (two copies of each chromosome) and gametes (egg and sperm) that are haploid (one copy of each chromosome). In the plant world, many fruits have more than the usual two sets (pairs) of chromosomes. Every cell in a strawberry contains eight copies of each of its chromosomes. As a result, strawberries contain large amounts of DNA.
Plant/fruit DNA is easy to extract (remove) because these materials can be squished. Plant/fruit cell walls are made mostly of cellulose, a carbohydrate that animals cannot digest. In order to extract the DNA, the carbohydrates need to be separated from the DNA. The following procedures will help you to do this.
Materials
· Graduated Cylinder -Measuring spoons -Rubbing alcohol/ethanol
· 2.5 g salt -80 mL of water -15 mL liquid soap
· Glass or small bowl -Filter paper -Funnel
· Beaker -3 strawberries (tops removed) -1 Test tube
· Resealable plastic sandwich bags
· 1 Bamboo skewer
Data/Results:
1) Describe the appearance of the DNA you extracted? Be sure to include color, shape, texture, odor, and other observations. Include a small-labeled drawing.
DNA You Extracted: ______
Description:
Drawing:
2) Describe the appearance of the DNA your neighboring group extracted (it should be different from yours)? Be sure to include color, shape, texture, odor, and other observations. Include a small-labeled drawing.
DNA They Extracted: ______
Description:
Drawing:
Analysis Questions: Answer the questions below using complete sentences. Do not use the word “it.”
1) How was the appearance of the DNA similar or dissimilar (like or not like) to what you have learned about DNA structure?
2) How did the data of the two different DNA samples extracted compare?
3) A person cannot see a single strand of cotton thread from 50 meters away (half a soccer field), but if thousands of threads are wound together into a rope, the rope can be seen at some distance. How is this statement an analogy to the DNA extraction you did?
4) DNA dissolves in water, but not in alcohol. Explain what happened when the alcohol came in contact with the strawberry/banana/wheat germ extract during the DNA extraction.
5) In order to study human genes, scientists must first extract the DNA from human tissues. Would you expect the method of DNA extraction for human DNA to be the same as the method you used to extract DNA from strawberries? Why or why not?
6) List two possible scientific questions that could be explored by studying strawberry DNA.
7) Strawberry cells are octoploid (each cell contains eight copies of chromosomes) where as banana cells are triploid (each cell contains three copies of chromosomes). Which do you predict will yield a greater quantity of DNA—5 g of strawberry tissue or 5 g of banana tissue? Explain your reasoning.
Experimental Procedure for Wheat Germ DNA Extraction
1. Put on your safety goggles.
2. Use the digital balance to weigh 1g of wheat germ. Put the wheat germ in a test tube.
3. Add 20 ml of hot tap water and mix gently but constantly for 3 min.
4. Add 1 ml of liquid soap and mix gently every 1/2 minute for 5 minutes. Try not to create foam. If you generated a lot of foam, use a folded paper towel to absorb it.
5. Tip the test tube at an angle. SLOWLY pour 15 ml of rubbing alcohol/ethanol down the side so that it forms a layer on top of the water/wheat germ/detergent solution. (Don't let the alcohol and wheat germ liquid mix. The DNA collects between the two layers!)
6. White, stringy or filmy DNA will appear at the interface of the two layers. Dip the bamboo skewer into the test tube where the alcohol and wheat germ layers meet. Pull up the skewer. The whitish, stringy stuff is DNA containing wheat genes!
Experimental Procedure for Strawberry DNA Extraction
1. Put on your safety goggles.
2. Mix 2.5 g of salt, 80 mL of water, and 15 mL of liquid soap in a beaker. Set the mixture aside. This is your extraction liquid.
3. Line the funnel with the filter paper and put the funnel's tube into the test tube.
4. Put the strawberries in the plastic bag and push out all the extra air. Seal it tightly.
5. With your fingers, squeeze and smash the strawberry mixture for 2 minutes.
6. Add 45 mL of the extraction liquid you made in Step 2 to the strawberries in the bag. Push out all the extra air and reseal the bag.
7. Squeeze the strawberry mixture with your fingers for 1 minute.
8. Pour the strawberry mixture from the bag into the funnel. Let it drip into the test tube until the test tube is ¼ full. DO NOT POKE A HOLE IN THE FILTER PAPER!
9. Throw away the filter paper and the strawberry pulp inside.
10. Tilt the test tube or jar and very slowly pour the cold alcohol down the side. The alcohol should form a layer on top of the strawberry liquid. (Don't let the alcohol and strawberry liquid mix. The DNA collects between the two layers!)
11. Dip the bamboo skewer into the test tube where the alcohol and strawberry layers meet. Pull up the skewer. The whitish, stringy stuff is DNA containing strawberry genes!
Experimental Procedure for Banana DNA Extraction
1. Put on your safety goggles.
2. Take a piece of banana and place it in a plastic bag. Add 20 mL of water to the bag and push out all the extra air and seal it tightly.
3. With your fingers, squeeze and smash the banana mixture for 2 minutes.
4. Mix 2.5 g of salt, 80 mL of water, and 15 mL of liquid soap in a beaker. Set the mixture aside. This is your extraction liquid.
5. Line the funnel with the filter paper and put the funnel's tube into the test tube.
6. Add 45 mL of the extraction liquid you made to the bag with the mashed banana. Push out all the extra air and reseal the bag.
7. Squeeze the banana mixture with your fingers for 1 minute.
8. Pour the banana mixture from the bag into the funnel. Let it drip into the test tube until the test tube is ¼ full. DO NOT POKE A HOLE IN THE FILTER PAPER!
9. Throw away the filter paper and the banana pulp inside.
10. Tilt the test tube and very slowly pour the cold alcohol down the side. The alcohol should form a layer on top of the banana liquid. (Don't let the alcohol and banana liquid mix. The DNA collects between the two layers!)
11. Dip the bamboo skewer into the test tube where the alcohol and banana layers meet. Pull up the skewer. The whitish, stringy stuff is DNA containing banana genes!