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With our Make: Science Room in full swing, I'm reminded of the Backyard Biology issue of MAKE. In Volume 07, we have articles that include freezing and reviving a garden snail, how to set up a home mycology lab, plant grafting and pollination, how to replicate your own DNA, and the cornerstone piece, Dr. Shawn Carlson's article on how to extract, purify, and experiment with DNA. Unfortunately, you can no longer get back issues of Volume 07 or the Next Year box set that it's a part of, but here's Dr. Shawn's article in full to get your biology wheels turning. Also, if you're a subscriber, you get full access to all 20 back issues of MAKE through our Digital Edition. And be sure to step into the Make: Science Room for tons more projects, tools, and techniques for backyard scientists.

Kitchen Counter DNA Lab
By Dr. Shawn

DNA is perhaps the most extraordinary structure in all creation. Its famous double helix is the longest molecule known and regulates the life processes in every cell on Earth. Even more, the code that DNA carries is the actual blueprint of life itself. The human recipe, for example, consists of roughly 3 billion molecular bits of information laid out in a precise sequence. Perhaps most amazingly, this miraculous winding staircase directly links every creature on Earth to our ancient and common past — far back to when evolution first began shaping the biological forms that would ultimately populate the world we know today. By examining the differences between the DNA in our bodies and that in other organisms, we can tell when our species diverged from chimps, apes, and even primordial fish.

The properties of this massive molecule are so mysterious and wondrous that most folks assume only the enlightened priesthood of laboratory biologists can extract and study it. Not so. In fact, anyone can extract, purify, and experiment with DNA at home.

When released from a cell, DNA typically breaks up into filaments. In solution, these strands have a slight negative electric charge, which makes for some very useful chemistry. For example, the more negative sections of one DNA strand will tend to attract the more positive regions of another. This causes DNA molecules to clump together and fall out of solution. However, if salt is added, its positive ions are attracted to the DNA's negative charges, effectively neutralizing them. This stops the fragments from adhering and keeps them floating in solution.

So, by controlling the salt concentration, anyone can make DNA fragments either disperse or clump together. And therein lies the critical secret of separating DNA from cells and manipulating it at home.

Isolating the DNA: Extraction

Here's how it works. First, you'll need a salty solution, called a buffer, into which DNA can dissolve. Next, you'll need to break open a bunch of cells and let their molecular "guts" seep out into your buffer. Then, you'll want to add a special enzyme that will destroy unwanted molecules, such as proteins, which would otherwise contaminate your results. Finally, you'll have to reduce the salt concentration enough to cause the DNA molecules to clump together and fall out of solution.

For the buffer:

Distilled or bottled water (glass 1) 120ml (about 4 oz)
Salt 1.5 grams (¼ tsp)
Baking soda 5 grams (1 tsp)
Liquid laundry detergent, dish detergent, or shampoo (glass 2) not soap — look for sodium lauryl sulfate on the label, 5ml (1 tsp)
Crushed ice to chill the buffer
Meat tenderizer
Pineapple juice, or contact lens cleaning solution just a dollop

For a source of DNA: Anything with living cells or cells preserved by freezing such as fruits, vegetables, legumes, fungi, meat from the butcher shop (a frozen cow tongue works great!), bone marrow from soup bones, etc.

To extract the DNA: Isopropyl (rubbing) alcohol (glass 3) with no additives and as concentrated as possible. Chill the bottle in the freezer before you begin.

Sundries: A drinking glass to mix the buffer, small narrow glass container (preferably with straight walls; a test tube is ideal, but a shot glass will do) to extract the DNA, narrow drinking straw to add the alcohol, a graduated test tube (or a plain one and a ruler with a centimeter scale) to measure the DNA, glass swizzle stick to remove the DNA.

Step One: Build the Buffer

First, you'll need to whip up your buffer. Pour 120 milliliters (about 4 ounces) of distilled or bottled water into a clean glass container. Add the table salt and baking soda, and stir vigorously. After they have dissolved completely, stir in the detergent. Shampoos and liquid laundry detergents that contain sodium lauryl sulfate (check the label) work well.

Next, add the meat tenderizer by wetting a toothpick, inserting it into the meat tenderizer, and transferring it to the buffer. Meat tenderizer contains an enzyme called papain that breaks up proteins so they won't come out with the DNA. Pineapple juice and contact lens cleaning solution also contain protein-busting enzymes, so, alternatively, you can add a drop of one of these 2 liquids.

Lastly, because DNA degrades fast (sometimes in a matter of minutes), you'll want to slow the pace of destruction by chilling the buffer in a bath of crushed ice. If the buffer becomes cloudy, you've chilled it too much. In that case, warm it just enough to clear it.

Step Two: Get the DNA

For a source of DNA, try the pantry. You can get great results with raw onions, garlic, bananas, or tomatoes. But it's your experiment; choose your own personal favorite fruit, veggie, meat (fresh or frozen), or fungus.

Once you've secured your DNA source, you'll need to process its cells to extract their organic molecules. First, use a knife to dice the material into small pieces. Put the material into a blender and pour in just enough distilled or bottled water to cover the chunks. Then break up (or lyse, as biologists say) the cells by pulsing the blades in short bursts until you've blended the material into a slushy mass. This will rip open some of the cells directly and expose many more cell walls and nuclei to the detergent's attack.

Finally, you need to leach out the organic molecules. Place 5ml (1 tsp) of the minced mush into a clean container. Mix in 10ml (2 tsp) of your chilled buffer. Swirl gently for 2 minutes, and the guts of the shattered cells will separate into the buffer intact. If you stir too vigorously, you'll break up some of the DNA.

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