It only takes a couple of minutes, and after you've isolated your own DNA, you can either drink it back down in a tasty "DNA shot" (great party trick) or better yet, purify it further for more analysis*.
Materials & Set Up
- 1/4 of a shot glass full of your saliva
- several drops of dish soap (look for sodium laurel sulfate in the ingredients)
- a pinch of table salt (1/16 of a teaspoon)
- some contact-lens cleaning solution, meat tenderizer, or pineapple juice (optional)
- Ice-cold 120-proof+ liquor (overproof rum works well)
The chemicals used in this experiment are "everyday" household items and are not particularly dangerous. Nonetheless, exercise extra caution and think twice if you decide to consume your DNA shot and ABSOLUTELY do not substitue rubbing alcohol, isopropyl alcohol, or any other non-consumable alcohol for the overproof rum we used. Besides using "denatured' alcohol, the other potential safety concern is the dishsoap added to the mixture. A couple drops won't hurt you, but if you are concerned about it, feel free to leave it out.
This instructable was produced by DIYbio - an organization for amateur biotechnologists. Visit diybio.org for more information.
EDIT: Some DIYbioers are developing a simple gel box and a gel box on steroids. We should have some instructables put together for them before Dec 08. If you are interested in helping, please join the DIYbio google group!
Step 1: Salivation...GO!
1/4 of a shot glass of saliva is harder to produce than you might think! Work your tongue against your cheeks and teeth as you think of a big juicy grilled steak / tofu cube / dim sum, or Muffins / baked cookies . I had to spit about 5 times to fill the glass 1/4th full.
If you are making the DNA shot for someone else, be sure to let them know where the DNA came from.
Step 2: Add a Couple Drops of Soap
Now that we have some saliva to work with, the first step is to break open (lyse) the cells it contains. We can do this by mixing in a couple of drops of the dish soap.
The detergents in the dish soap (like the sodium laurel sulfate, aka sodium dodecyl sulfate) destabilize the membranes of the cells, spilling their contents into the rest of the solution of saliva. This includes all of the cytoplasmic and nuclear proteins, sugars, and yes, nucleic acids (DNA! and rna.) But all of this stuff is still dissolved in the saliva. The rest of the steps will cause the DNA to aggregate and precipitate out of solution.
Step 3: Some Protease...
Now that we've busted open the cells, they've spilled their guts all over the place in our saliva solution. in this step we try and get rid of as much of the protein part of those guts as we can.
A protease is a type of enzyme that can break down other enzymes. Meat tenderizer, pineapple juice, and soft contact lens cleaning solution all contain (different) proteases. A tiny bit of any of those should reduce the amount of protein that precipitates out with our DNA later on.
Step 4: And a Pinch of Salt
Just add a pinch of table salt to the soapy saliva. I used less than 1/16th of a teaspoon, and that was probably too much.
So what's the deal?
Although we have freed the DNA from the cells, it's still dissolved in the solution. To get the DNA to precipitate and solidify, we need to do something about each molecule's negatively-charged phosphate backbone.
When we dissolve the table salt in the solution, some of the positively-charged Sodium ions will interact with the negatively-charged regions of the DNA molecules and effectively shield other nearby DNA molecules from their repulsive force - this will help them all aggregate and clump together in the next step.
To visualize the idea here, imagine the resistance you feel when you begin to push the south poles of two magnets together - this is sort of like what's going on between the individual DNA molecules. Now imagine inserting the north pole of a third magnet between the south poles of the first two - the resistance is reduced. The north pole of the third magnet is sort of like the Sodium ion in our solution.
Step 5: Pour on a Layer of the Rum
Mix the solution in the shot glass for a minute by gently shaking and rocking the glass.
Now gently add a layer of the overproof rum to fill up the shot glass. The best way to do this is by tilting the shot glass and transferring the rum over a little bit at a time using a straw. If you have a steady hand, however (or just think you do, like me), you can try and slowly pour the icy-cold rum from the bottle onto the top of the saliva in the shot glass. The key thing here is to prevent the alcohol from mixing much past the surface of the saliva.
You should see some cloudy, snot-like white stuff suddenly appear near the boundary between the saliva and alcohol as you add the alcohol. This is DNA (and probably a lot of other cellular junk) precipitating out of solution!
What's going on? DNA is not very soluble in alcohol, so some of the free DNA at the surface of the saliva solution immediately precipitates when we begin to add the alcohol. Other, deeper DNAs are pulled out of solution by the precipitating DNAs into the alcohol, and suddenly we end up with this visible floating mass of DNA. You can see the precipitate in the second photo.
Step 6: Spool Your DNA
If you are in a playful mood, you can use a small rod like a toothpick to spool up your DNA. Insert the toothpick into the DNA precipitate and gently swirl it around, rotating the toothpick at the same time. You're trying to wind the filaments of precipitated DNA around the tip of the toothpick.
Once you think you've got them, you can slowly lift the toothpick out of the solution. You should see it trailing a thin strand... of DNA! (check out the second picture; note that my shot glass has a red yelp logo on it)
At this point, you could prepare the spooled DNA on the toothpick for use in another experiment - for instance, you might be interested in staining the DNA to make sure you actually extracted some of it, or in running it on a homemade gel to separate all the different fragments of DNA by their length. Or you might try and prepare for sequencing (but you would probably need to purify the sample first)
Step 7: Tastes Like DNA!
I decided to drink my DNA shot. I thought my body might resent the fact I had taken some of its DNA - the blueprint and program that defined how it grew into what it is today - and not shared any with it. Also, I wanted to see if my DNA had a particular taste.
Results: the DNA shot tastes like very potent, cheap rum. But it was one of the best drinks I can remember making.
Safety Note: be sure you are using consumable alcohol bought from a liquor store - anything else will poison you. Be safe, and think twice before you mindlessly follow directions.
More information about the chemistry of the DNA precipitation reaction and other version of the DIY DNA extraction protocol can be found here:
- Kitchen Kitchen Counter DNA lab
- The Macgyver Project: Genomic DNA extraction and Gel Electrophoresis using everyday materials
- How to extract DNA from anything living
- The Basics: How Ethanol Precipitation of DNA and RNA Works
- The Science of DNA precipitation by madsci.org
- Mac from diybio.org