Biotechie’s Bucket Biology on the Cheap: Gatorade DNA Extraction!

2015 6-18 Blog

By: Biotechie
Image by: Amber D. Miller

Before I began my PhD studies, some of my favorite experiences happened during my participation in an undergraduate organization that took science to middle school and high school classrooms. I would go to these tiny little rural classrooms, which lacked even the most basic lab equipment, like a scale, and would take with me a thermocycler, gel electrophoresis rig, and all of the rest of the equipment needed to show these students over a morning workshop how to get the pretty DNA banded gels like you see on CSI. These experiments would get the students excited about science, and I was inundated with questions about how I became a scientist.

At the end of the day, I would meet with the teachers and talk about how to incorporate more lab experiments in their classrooms, as hands-on experiments are a key factor in learning and maintaining interest in science. As is a common and unfortunate trend throughout the United States, the biggest concern was money. Many of these schools are given no budget for lab work, and so, over time, I began to work with these teachers to modify and develop experiments they could do with their classrooms for less than $20, what I like to call “Bucket Biology on the Cheap.”

As a Science ACE, I think it is important that these experiments are available to the public as a resource for teachers trying to generate lesson plans and incorporate more hands-on fun in the classroom and for others who are interested and want to try it out!

The Gatorade DNA Extraction is a tried and true experiment often used in high school classrooms. You can easily do this at home or at school, so it truly is an experiment for everyone! We tweaked it and made sure it worked, so here is the streamlined version that I used during outreach:

Materials Needed:

Small disposable cups

5 mL Lemon-Lime Gatorade (must be original, not sugar-free or G2) per student

5 mL ice cold 90-100% ethanol (store in freezer overnight – it will not freeze)

2 mL 25% dishwashing detergent (25 mL Dawn + 75 mL water)

15 mL test tubes or screw-cap tubes

Thin bamboo skewers for spooling DNA

Where to buy materials:

All of the materials you need for this experiment can be purchased inexpensively. However, you may not have purchased materials like pipettes, ethanol, or test tubes before, so to save you some time, here’s where you can find these items:

  • Plastic pipettes to measure accurate volumes in mL can be purchased from many craft stores. It may also be helpful to know your conversions: 5 mL is approximately equal to 1 tsp.
  • 90-100% ethanol, or ethyl alcohol, can be purchased from some grocery stores. It can also be purchased from hardware stores, where it is labeled as denatured alcohol, or from liquor stores as 190-proof Everclear.
  • Test tubes can be purchased online, from supermarkets, or from a craft store.

Protocol:

(Make sure students do not eat or drink anything for an hour or so before the experiment so you get more cells and no food chunks)

  1.     Take the 5 mL aliquot of Gatorade and swish it around your mouth like mouthwash for 30 seconds. Spit it back into the cup and transfer it into your tube.
  2.     Add 2 mL of the 25% dishwashing detergent solution, cap/stopper the tube, and invert gently several times to mix. Do not shake! Then let the tube sit for a few minutes so the solution can work and to allow bubbles to pop.
  3.     Hold the tube at an angle and VERY slowly pour the ice cold ethanol down the side of the tube. You should see a clear layer forming on top of your Gatorade layer. Be very careful not to shake or jostle the tube!
  4.     Within a few seconds, you should see a white filmy layer between the Gatorade and ethanol layers. This is the DNA! Without shaking the tube, gently slide a skewer all the way to the bottom of the tube and slowly spin it. You will see the DNA start to stick to the skewer at the interface. Slowly pull the skewer out.
  5.     You can dry the DNA on the skewer or collect it into a microcentrifuge tube using a toothpick to keep as a souvenir!

Explanation of how each step works:

  1.     We drink Gatorade when we play sports because it replenishes the electrolytes we lose while sweating. Gatorade is isotonic to our own cells, which means that the salt and ion concentrations are very similar to what is inside our cells. This helps keep the cells from lysing before we want them to. The cells in your mouth are only attached loosely to one another, which is why you can get enough from this experiment by vigorously swishing the solution around your mouth.
  2.     Why would it be important to add a detergent to the cells you collected with the Gatorade? The detergent is amphipathic, meaning that it has one end that is hydrophobic (water-hating) and one side that is hydrophilic (water-loving). The membrane surrounding each cell is composed of a lipid bilayer which consists of a hydrophobic center and a hydrophilic outer portion. Because it is amphipathic, the detergent molecules are able to invade the lipid bilayer and cause it to fragment into many small micelles, surround proteins to break up protein interactions, and ultimately release the DNA from the cell!

At this step, the Gatorade is also helping us out. The salt ions in the Gatorade help protein fragments and other cell debris to clump together, which is why you may start to see some chunks floating to the bottom of your tube. That’s okay! Your DNA should still be in solution.

  1.  and 4.  We always talk about “like dissolves like” in the lab when we talk about polarity. Polar molecules, like water, have a slight positive charge on one end and a slight negative charge on the other end. DNA is very polar with a net negative charge when it is in solution. Both water and ethanol are polar, but ethanol is much LESS polar than water, particularly when the ethanol is very cold. This means that the difference between the positive and negative charges are in ethanol are not as great across the molecule.  The DNA is coated in Na+ ions from the salt in the Gatorade, making it even more polar.  The highly polar DNA cannot dissolve in the much less polar ethanol, so it precipitates into a white, wispy layer when cold alcohol is added.

I hope you enjoyed this experiment! What do you want to learn about next?

Sources: Adapted from DNA extraction protocols used in the laboratory and lesson plans utilized by Biotechie during outreach, and with generous help from University of Utah (http://learn.genetics.utah.edu/content/labs/extraction/).

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