Wednesday, June 26, 2013

Extracting Strawberry DNA

DNA was a hard topic for my students to grasp because they couldn't SEE DNA.  We watched several videos and looked at many diagrams, but they still didn't understand.

After I attended the NSTA conference I was energized to come back and help my students have a better understanding.

I did this by conducting the Extracting Strawberry DNA (click for link) lab.

Materials (per person) 

 1 resealable plastic bag   (Don't use the cheap ones, you need them to stay together as your mix your solutions)
 Strawberries (fresh or frozen)  (I've only done it with frozen, but I'm going to try fresh next time)
 2 teaspoons of dish detergent  
 1 teaspoon of salt 
 ½ cup of water 
 2 plastic cups (One cup will be used for the filtering apparatus below) 
 Filtering apparatus: coffee filter and plastic cup 
 Ice cold 90 percent rubbing alcohol 
 1 wooden popsicle stick or plastic coffee stirrer 


1. Pull off any green leaves on the strawberry that have not been removed yet. 
2. Put the strawberry into the plastic bag, seal it and gently smash it for about two minutes.  
Completely crush the strawberry. This starts to break open the cells and release the DNA.  
3. In a plastic cup, make your DNA extraction liquid: mix together 2 teaspoons of detergent, 1 
teaspoon of salt and ½ cup of water.  
4. Add 2 teaspoons of the DNA extraction liquid into the bag with the strawberry. This will further 
break open the cells.  
5. Reseal the bag and gently smash for another minute (Avoid making too many soap bubbles). 
6. Place the coffee filter inside the other plastic cup. 
7. Open the bag and pour the strawberry liquid into the filter. You can twist the filter just above the 
liquid and gently squeeze the remaining liquid into the cup.  
8. Next, pour down the side of the cup an equal amount of cold rubbing alcohol as there is 
strawberry liquid. Do not mix or stir. You have just isolated the DNA from the rest of the material 
contained in the cells of the strawberry. 
9. Within a few seconds, watch for the development of a white cloudy substance (DNA) in the top 
layer above the strawberry extract layer.  
10. Tilt the cup and pick up the DNA using a plastic coffee stirrer or wooden stick.

The students watched and helped me do the experiment, but in order to save time and money I conducted the actual experiment.  Afterwards, we took the DNA and looked at it under the microscope.    We couldn't see anything, so students suggested (YAY!!) that we dye it!  

The white floaty stuff are the DNA strands.

Have you done this experiment before?  I've heard it can be done with grapes!!

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