The folks at NOVA PBS have made a great short video that shows everyone how they can extract their own DNA using common
household items! It does work, and you don't have to use only strawberries or chicken livers, it's (almost) 100% you!
Before you try it on your own, you might like to know the first DNA to be isolated was accomplished in Germany in 1871,
isolated from pus on bandages from a hospital, by Friederich Miescher. He isolated compounds that were rich in phosphorus
and nitrogen, but not sulfur (proteins have sulfur, nucleic acids such as DNA and RNA do not).
Pus is loaded with white
blood cells that are first on the line of defense in case of an injury or inflammation, called neutrophils. If you want
to learn more about neutrophils (and how they are used in forensics to differentiate
between a male and female victim, among other fun facts), you might want to watch my video about them in the Blood Cell Bakery Series . The image to your right is a single neutrophil. The blue stained structure is the nucleus, which has a funny shape
compared to the images in your textbooks, but this helps these cells squeeze out of blood vessels to damaged tissues quite
easily.
If you follow these instructions, you are isolating DNA from
the epithelial cells in your cheek, and probably some from the bacteria that naturally inhabit your mouth. Having isolated
DNA in the lab, I thought I should I explain here what the purpose of each step is, as some people have asked me about them.
The steps in this video are similar to steps used in the lab, although in the lab we work hard to obtain very pure samples
for analysis and manipulation.
Notice you only require three solutions: salt water, detergent and isopropyl
alcohol.
To obtain any biological specimen, you will want to use salt water in your preparation as
it is an isotonic solution, meaning you won't destroy the cells right away due to an osmotic disruption. (If you want to know
more about osmosis, check out Gummi Bears demonstrate osmosis) In addition, the presence of salt during your prep will neutralize the charges on the sugar phosphate backbone, making
it less soluble in water.
The detergent breaks apart the cell and nuclear membranes. The chemical structure
of soap molecules are able to disrupt the cell membrane. It is essentially poking holes in the fatty (lipid) membranes of
your cells, wrapping up the lipids and carrying them away. It also will help unravel the DNA. Check out the description on Wikipedia for more info!
The alcohol causes the DNA to clump together and drop out (precipitate) of
solution so you can collect it. This has to do with the electrostatic attraction between the sodium ions you added in your
salt solution and the phosphate ions that are on the DNA backbone. Ultimately in salt water, the sodium and phosphate ions
are not going to be very close together. But in ethanol, the sodium and phosphate come together easily. The phosphate's negative
charge is hidden, which makes the DNA (and RNA) less hydrophilic (water loving), and it will then drop out of solution into
that stringy mess you try to spool up onto a stick or a stirring rod much like you would a spider's web on a stick (a slimy
one, for sure).
This will not be a very clean prep for two reasons: 1) you will most likely also have the
DNA from the bacteria in your mouth in the and 2) there might also be a lot of carbohydrate mixed in as well.
In
the lab, we refine our salt solutions, work with various temperatures and use equipment like centrifuges to get the best possible
sample. After that, we can manipulate and analyze the DNA for many purposes useful in forensic and molecular analysis.
But for you, it is fun that you've managed to retrieve what seems invisible, even though we see it working all
the time. A great website for all things DNA, including how and why to extract it, is at Learn Genetics, one of my favorite websites!
If you give this a try, send along your photos and tell me all about it! I'd
love to hear how it worked for you!
