Did you know extracting your DNA so you can see it with your own eyes is one of the easiest science projects you will ever do? Take a look at the video below and try it out for yourself! We’ve also included some cartoons from The Baby Biochemist: DNA to illustrate what is happening during each step!

 

Materials

• small glasses/ plastic cups/ test tubes (transparent so you can see the DNA)
• water
• table salt
• dish detergent (not dish washer detergent)
• rubbing alcohol (isopropanol or isopropyl alcohol)

Method

1. Add about 1/4 tsp salt to 1/4 cup water and swirl to dissolve (doesn’t have to totally dissolve).
2. Take a sip and swish in your mouth for at least one minute, making sure to scrape your cheeks with your molars while you swish to get a good sample of cheek cells.
3. Spit the salt water into a new small glass or test tube.
4. Add one drop of dish detergent and stir. If in test tubes, close the tube and invert to mix. Try not to make bubbles.
5. Tilt the glass or tube slightly and gently pour the rubbing alcohol down the side of the glass so that it forms a layer on top. Be careful not to mix or disturb the layer, as rubbing alcohol and water are miscible.
6. After a few minutes, you will see white stringy clumps enter the rubbing alcohol layer. This is your (and the bacteria-in-your-mouth’s) DNA!

Discussion

Swishing the salt water in your mouth removes cheeks cells. This is just an easy, painless way to get some of your cells.

The detergent disrupts the membranes of the cells (the outer cell membrane and also the organelle membranes), spilling their contents into the salt solution. (I forgot to “spill” the mitochondria and Golgi in the illustration below, but you get the point 😉 )

 

DNA exists in your cells wrapped up with proteins in chromosomes.

The detergent and salt in the water will help to release the DNA from these proteins. DNA has negative charges all along the length of it. DNA-binding proteins use “electrostatic interactions” to stick to the DNA, which just means most DNA-binding proteins have positively charged pockets on them which stick to the negatively charged DNA (opposites attract!). The large amount of salt in the water, which is now negatively and positively charged ions, will interfere with the DNA-protein interactions and free the DNA. The ions interacting with the DNA also make the DNA less soluble in water.

When you add the rubbing alcohol, the DNA/salt complexes will travel to that layer and clump together, eventually precipitating.

Even though the precipitated DNA floating in the rubbing alcohol looks pretty stringy, these strings are not the individual strands of DNA. They are tons and tons of the strands stuck together (otherwise it wouldn’t be visible to our eyes), but coincidently still look like strings when it precipitates. Still, that dust bunny looking thing is DNA!

This method is actually pretty close to how we precipitate DNA in actual labs, (just with a few extra purification steps and different reagents), so feel free to feel like a real scientist when you’re trying it out!

If you would like to learn more about DNA with your kids, check out our book, The Baby Biochemist: DNA, available on Amazon!