Lessons Direct

This laboratory comes straight from genome.gov/strawberry-DNA . Thank you to the United States National Institutes of Health’s National Human Genome Research Institute.

Warm-Up Questions:

1. Where is DNA located?
   
2. What is DNA’s role in a cell?

Materials (per scientist):
2 Strawberries, fresh or frozen
1 Resealable Plastic Bag (Quart-sized or larger)
2 teaspoons of Dish Detergent
1 teaspoon of salt
1/2 cup of water
1 coffee filter
2 plastic cups
1/2 cup of cold rubbing alcohol
1 coffee stirrer
1 marker

Before you start:
1. Are any of the materials considered dangerous? (Ask an adult to help you search)


2. Do all of the instructions make sense, or should you draw it out first?

Methods:

1. Pull of any green leaves on the strawberries.
2. Put the strawberries into the plastic bag and seal it.
3. Gently smash the strawberries for ~2 minutes until they are mushed and smooth. (You are lysing the strawberries.)
4. Mix together 2 teaspoons of detergent, 1 teaspoon of salt, and 1/2 cup of water in a plastic cup. Label the cup DNA Extraction Liquid.
5. Pour the DNA Extraction Liquid into the bag with the strawberries.
6. Reseal the bag and gently smash for another minute. The lysis buffer will further lyse the strawberry cells and release the DNA inside.
7. Place the coffee filter inside the second plastic cup. You might want to fold the filter so that it is secure on the top.
8. Pour the contents of the strawberry-DNA Extraction Liquid bag into the coffee filter. Squeeze the bag so all of the mixture enters the coffee filter. Get as much liquid into the cup as you can.
9. Lift the filter and twist it just above the liquid to squeeze any remaining liquid through the filter and into the cup. Get as much liquid into the cup as you can.
10. Determine how much liquid is inside your plastic cup.
11. Carefully pour an equal amount of rubbing alcohol as there is strawberry slurry by tilting the cup and pouring along the side of the cup. Set the cup down and do not disturb the mixture.
12. After several seconds, a white cloudy substance (DNA) will develop on the top of the mixture.
13. Tilt the cup and pick up the DNA using a coffee stirrer.

Notes:

Did you make any mistakes while you were working? Describe them.

What steps could have been explained better?

Reflective Questions:

1. What did the DNA that you extracted look like? How did it move?
   
2. Why couldn’t you see the DNA before you followed the laboratory instructions? (Where was the DNA?)
   
3. Where was the DNA before you added the rubbing alcohol? Why couldn’t you see it before? (Think about solubility and visibility.)
   
4. How did you break the cells open to release the DNA? What did the ingredients in the DNA Extraction Liquid do? (And what did your hands do?)
   
5. Instead of a coffee stirrer, what else could you have used to collect the DNA? What would make that better than a coffee stirrer?
   
   
   
6. Store-bought strawberries have 8 of each set of chromosomes, making them octoploids. They have 7 sets. How many chromosomes does a strawberry have?
   
   
7. Store-bought bananas have 33 chromosomes (three sets of 11, triploids). If the laboratory had used two bananas instead of two strawberries, do you think you would have collected more DNA, the same amount of DNA, or less DNA? Why?
   
   
   
8. What do you think happens to the DNA in the strawberries that you eat?
   
   
   
9. If a scientist created a special blue-colored, ultra-sweet strawberry by changing the strawberry’s DNA, do you think some of those DNA changes could pass on to you when you eat the strawberry?
   
   
10. Do all living things have DNA? Is it possible to extract DNA from all living things?
    
    
11. Would it be easier to extract DNA from a softer fruit? What about from a fruit with more water content, like a watermelon?
    
    
12. Why do scientists extract DNA in their laboratories? What are some real-world applications of DNA extraction?
    
    
13. If you did a poor job crushing the strawberry or forgot an ingredient in the DNA Extraction Liquid, what would happen? Would you see DNA?
    
    
14. If you poured the rubbing alcohol directly into the liquid instead of pouring it along the side of the cup, what do you think would happen?
    
15. What questions do you still have after completing this experiment?
    

Future Direction

Review your answers, notes, and the methods again. Create a follow-up laboratory to test one of your hypotheses. You may improve the original methods as long as your mentor thinks it is safe and possible.