California Content Standards Addressed:
Life Sciences (7th grade) 2.e Students know DNA (deoxyribonucleic acid) is the genetic material of living organisms and is located in the chromosomes of each cell.
Biology (9th -12th) 5.c. Students know how genetic engineering (biotechnology) is used to produce novel biomedical and agricultural products.
1 resealable plastic bag Strawberries (fresh or frozen)
2 teaspoons of dish detergent
1 teaspoon of salt
1⁄2 cup of water 2 plastic cups (One cup will be used for the filtering apparatus below)
Filtering apparatus: cheesecloth and plastic cup, rubber band
Ice cold 90 percent rubbing alcohol
Students will be told that they are going to extract DNA from a strawberry. Students will then write down three new questions or ideas they have about what is going to happen.
Then Students will be asked to work in groups and share their questions.
After they have shared their questions the students will then be asked what do you think extract means? Students will then work in groups to define extract.
Other Pre-lab questions would include "Where can DNA be found in the cell?"
Finally students will set up a observation/procedure table the day before the activity, so they have two exposures to the procedure.
1. Place the strawberry in the plastic bag, seal the bag and GENTLY SMASH the strawberry inside the bag for two minutes Make sure to completely smash the strawberry because we need to break open the cells and release the DNA from inside the nucleus.
2. Take your plastic cup and mix your DNA extraction solution. MIX: 2 teaspoons of detergent, 1 teaspoon of salt, and 1/2 cup of water.
3. Add a small amount (a few teaspoons) of the DNA extraction solution made in step 2 into the bag with the smashed strawberry.
4. SEAL the bag and gently smash the strawberry again for two minutes (avoid vigirous smashing to avoid soap bubbles)
5. Take your second plastic cup and place the cheesecloth over the top of the cup and place a rubber band around the outside of the cup securing the cheesecloth
6. Open the plastic bag and slowly pour the strawberry liquid into the filter.
7. After finished pouring the strawberry liquid onto the filter remove the filter.
8. Next, take the cold rubbing alcohol and pour it down the side of the cup. The amount of rubbing alcohol added should be approximately equal to the amount of liquid strawberry you have. You do not need to stir or mix the solution. The DNA will separate from the rest of the material at this point.
9. You should be able to see a white cloudy substance on the top layer of the strawberry extract.
10. Tilt the cup and use the paper clip to pick up the strawberry DNA.
Student Prior Knowledge
This activity is designed to help students intrigue students. This activity will be performed after students learn about DNA and just before we learn about Genetic Engineering. Students will perform a pre-procedure part of the lab the day before the activity.
Question and Answer
Applications to Everyday Life
This activity allows students to "work like a scientist". Students get the opoportunity to do an extraction of the DNA and have a better understanding of how DNA can be extracted. Students can use this information to relate it to crime scene investigations, gene sequencing, biotechnology, and diseases caused by mutated DNA