Introduction: DNAquiri: the Delicious DNA Extraction
Extracting DNA from spit or fruit is a favorite science faire / Maker Faire demo. This is the adult version of that science demo, inspired by Mac Cowell's 5 minute DNA Extraction in a Shot Glass instructable. Especially his final picture, where he drinks his own salt-detergent-rum spit cocktail. :-D Hey, if you're going to use high-proof rum, you might as well make it tasty, right?
Extracting DNA from plant or animal sources is a fairly straightforward procedure, and can even be done at home. However, to our knowledge, no one had previously created a DNA extraction protocol that also functions as a cocktail recipe. The DNAquiri is an attempt to fill this scientific void. The cocktail consists of a strawberry puree layer and an alcohol layer, where the DNA from the strawberries is extracted into the alcohol layer. Because DNA is an extremely long polymer, when it clumps together in the alcohol layer it forms long strands that are visible to the naked eye and can be picked up with a toothpick.
This is a project that was developed and presented (and won Best In Show!) at Science Hack Day San Francisco 2011. http://sf.sciencehackday.com/
Step 1: Gather Supplies
ice cold Bacardi 151
frozen sliced strawberries
frozen pineapple juice concentrate
Scale or measuring cups
Narrow glasses for serving
This ingredient list differs significantly from the materials for a standard home DNA extraction. Key changes:
-Normally, surfactants such as dish soap are used to lyse cells. These are not very tasty. Instead, we start with frozen strawberries, in which most cells have already been lysed by the freeze/thaw process. We found that no surfactant was necessary when starting with frozen fruit. Strawberries also gave us the most DNA by far, probably because commercial strawberry strains tend to be octoploid, i.e. they have 8 copies of DNA per cell. (See also How To Extract DNA From A Strawberry.)
-Salt is usually added to enhance precipitation of the DNA. We found salt unnecessary and were able to obtain reasonable yields while omitting it.
-Meat tenderizer is often added to help break down proteins and free the DNA; this mimics the effect of proteases that would be used in a lab setting. Instead, we used pineapple juice, which contains the protease bromelain. (Note that canned pineapple should not be used, since the heat used during the canning process deactivates bromelain.)
-High-proof alcohol (greater than 80 proof) is required for DNA precipitation. Since a daiquiri would traditionally be made with rum, we selected Bacardi 151. (Cheapskates can use Everclear - both are 151 proof, or 75%.)
Step 2: Measure Out Ingredients
Put 250 g strawberries (about 2 cups) and 75 g pineapple juice concentrate (about 1/4 cup) into a ziplock bag and seal it. Gently crush the strawberries with your fingers into a pulp. Best not to use a blender for this step, because it will chop up the DNA as well.
Step 3: Heat and Cool
Microwave a bowl of water to about 50-60 degrees C (if you don't have a thermometer handy, aim for hotter than bathwater, but not hot enough to burn your finger). Heat the ziplock bag of fruit in the hot water bath for 10 minutes, then place the bag in an ice bath for 10 minutes.
Step 4: Strain
Strain the fruit pulp, using a spoon to push it through the mesh. This step removes large chunks that make the drink a little bit chunky.
Step 5: Serve
Put about 50 ml of fruit pulp into a glass, then gently layer 10 ml of ice cold Bacardi 151 on top. The strawberry DNA will be extracted into the alcohol layer. Swirling the glass gently may help promote DNA moving into the alcohol phase. If you prepare the cocktails in advance, don't wait more than 15 minutes before serving. You'll extract more DNA as time goes on, but the DNA will start degrading after that.
Add a tiny umbrella; DNA can be collected onto the end of the umbrella's toothpick by twirling it, if desired.
Step 6: Results and Conclusions
During the protocol development process, we received comments on early versions such as "gross", "salty", and "tastes like soap." We are pleased to report that feedback on the final product was generally positive. The DNA looks disconcertingly snotty when freshly extracted, but the texture was not really noticeable when drinking.
You'll have a layer of very high proof rum on top of you cocktail, so before drinking--or even sipping--you'll probably want to mix the alcohol into the fruit puree.
Tasters enjoyed the ability to scoop up their drink's DNA on the end of a toothpick (pictured), and found the whole experience rather intoxicating. Or maybe it was just the rum.
First Prize in the
The Mad Science Fair