Fred Truman

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Strawberry DNA Extraction

September 21, 2011

Assignment: Conduct your first lab experiment by extracting DNA from strawberries. Document your process and results. Make notes of any issues and jot down any questions as we’ll discuss your experience in class next week. If you have done this experiment before, see if you can come up with a more streamlined protocol using less or even different reagents (ingredients) or try experimenting with different fruits or vegetables.

Materials:

1. Strawberries (at least 2 juicy ones)
2. Quarter teaspoon of Table salt (NaCl) – don’t use too much of this!
3. A teaspoon of dishwashing detergent (We used the brand Joy, but any brand will do)
4. Meat Tenderizer (McCormicks brand, again, any brand should work)
5. Half a glass of water
6. Ziplock baggie (1 quart volume)
7. A disposable coffee filter
8. A plastic funnel (you may be able to hold the filter some other way in the glass)
9. Chilled Rubbing alcohol (We used 91% isopropanol, which works better than the 70% strength)
10. Ice or a fridge to cool the rubbing alcohol prior to using
11. A tall drinking glass (don’t drink this stuff)
12. A thin wooden stick (used to fish out your DNA)

Protocol:

• Step 1:
 Drop the strawberries into a ziplock baggie.
• Step 2: 
Add the detergent, meat tenderizer and salt.
• Step 3:
 Seal the baggie and “mechanically disrupt the cells”. Start squishing the cells. Squish and mix them really well with all of the ingredients. Knead the bag for about 5 minutes until you have the consistency of a smoothie
• Step 4:
 Open the baggie and add some water. Shake it up a little.
• Step 5:
 Place your filter in the funnel and place this in the glass. Now pour the contents of the baggie (the squished strawberry mixture) into the filter.
• Step 6: 
Let the contents drip through the filter into the glass. It should look milky pink. Be patient! If the filter is working too slowly, you can gently squeeze it, but not too hard or it may break.Step 7: 
Holding the glass at an angle, very slowly pour the chilled rubbing alcohol down the side into the strawberry mixture. You want to pour it slow enough so that a layer of the clear alcohol forms on top of the pink layer underneath, since the alcohol is less dense than the water layer containing the strawberries. If you pour too quickly you won’t see this layer form, so remember to do it slowly. Pour enough alcohol so that you have at least a 2 inch layer on top.
• Step 8: 
Now set your glass down. You should start to see a wispy/filamentous white layer start to form between the bottom pink layer and the clear alcohol on top. It should take about a minute or more to develop. It will start to look like a small ball of cotton. Sometimes it looks like many small pieces of cotton. Give it some more time and it will gently rise to the surface. This is the strawberry’s DNA starting to precipitate!
• Step 9: 
Using your thin wooden stick, you can now fish out the DNA. It will be rather “stringy” since DNA molecules form long chains. These types of molecules are known as “polymers”.

all contents ©2009-2010 Fred Truman