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DNA Extraction Made Easy
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DNA Extraction Made Easy

By Dr. Louisa Stark - Posted Mar 10, 2005

Desoxyribonucleic acid! You mean I can see it? How?

Just follow these 3 easy steps:

Detergent

eNzymes (meat tenderizer)

Alcohol

It's that simple? Tell me more!

First, you need to find something that contains DNA. Since DNA is the blueprint for life, everything living contains DNA. For this experiment, we like to use green split peas. But there are lots of other DNA sources too, such as:

  • Spinach
  • Chicken liver
  • Onions
  • Broccoli

Here's the fun part. Put these items in a blender:

  • Your DNA source (about 100ml or 1/2 cup of split peas)
  • A large pinch of table salt (less than 1ml or 1/8 teaspoon)
  • Twice as much cold water as the DNA source (about 200ml or 1 cup) 

Blend on high for 15 seconds. The blender separates the pea cells from each other, so you now have a really thin pea-cell soup. Because this step is pretty messy, certain sources of DNA should not be used, such as your family dog or close relation.


And now, those three easy steps:

1. Pour your thin pea-cell soup through a strainer into another container (like a measuring cup).

How much pea soup do you have? Add about 1/6 of that amount of liquid detergent (about 30ml or 2 tablespoons) and swirl to mix. Let the mixture sit for 5-10 minutes.

Pour the mixture into test tubes or other small glass containers, each about 1/3 full.

Try any detergent you may have on hand. (Why am I adding detergent?)

2. Add a pinch of enzymes to each test tube and stir gently. Be careful! If you stir too hard, you'll break up the DNA, making it harder to see.

Use meat tenderizer for enzymes. If you can't find tenderizer, try using pineapple juice or contact lens cleaning solution. (What is an enzyme?)

3. Tilt your test tube and slowly pour rubbing alcohol (70-95 percent isopropyl or ethyl alcohol) into the tube down the side so that it forms a layer on top of the pea mixture. Pour until you have about the same amount of alcohol in the tube as pea mixture.

DNA will rise into the alcohol layer from the pea layer. You can use a wooden stick or other hook to draw the DNA into the alcohol.


What is that stringy stuff?

 
Alcohol is less dense than water, so it floats on top. Since two separate layers are formed, all of the grease and the protein that we broke up in the first two steps and the DNA have to decide: "Hmmm...which layer should I go to?"

This is sort of like looking around the room for the most comfortable seat. In this case, the protein and grease parts find the bottom, watery layer the most comfortable place, while the DNA prefers the top, alcohol layer. DNA is a long, stringy molecule that likes to clump together.


Congratulations! You have just completed a DNA extraction!

Now that you've successfully extracted DNA from one source, you're ready to experiment further. Try these ideas or some of your own:

  • Experiment with other DNA sources. Which source gives you the most DNA? How can you compare them?
  • Experiment with different soaps and detergents. Do powdered soaps work as well as liquid detergents? How about shampoo or body scrub?
  • Experiment with leaving out or changing steps. We've told you that you need each step, but is this true? Find out for yourself. Try leaving out a step or changing how much of each ingredient you use.
  • Do only living organisms contain DNA? Try extracting DNA from things that you think might not have DNA.

Many thanks to Dr. Louisa Stark and the University of Utah Genetic Science Learning Center, where this article was originally published.

Click on page 2 for the DNA Extraction FAQ!

DNA Extraction FAQ

1. I'm pretty sure I'm not seeing DNA. What did I do wrong?

First, check one more time for DNA. Look very closely at the alcohol layer for tiny bubbles. Often, clumps of DNA are loosely attached to the bubbles.

If you are sure you don't see DNA, then the next step is to make sure that you started with enough DNA in the first place. Many food sources of DNA, such as grapes, also contain a lot of water. If the blended cell soup is too watery, there won't be enough DNA to see. To fix this, go back to the first step and add less water. The cell soup should be opaque, meaning that you can't see through it.

Another possible reason for not seeing any DNA is not allowing enough time for each step to complete. Make sure to stir in the detergent for at least five minutes. If the cell and nuclear membranes are still intact, the DNA will be stuck in the bottom layer. Often, if you let the test tube of pea mixture and alcohol sit for 30-60 minutes, DNA will precipitate into the alcohol layer.


2. Why does the DNA clump together?

Single molecules of DNA are long and stringy. Each cell of your body contains six feet of DNA, but it's only one-millionth of an inch wide. To fit all of this DNA into your cells, it needs to be packed efficiently. To solve this problem, DNA twists tightly and clumps together inside cells. Even when you extract DNA from cells, it still clumps together, though not as much as it would inside the cell.

Imagine this: the human body contains about 100 trillion cells, each of which contains six feet of DNA. If you do the math, you'll find that our bodies contain more than a billion miles of DNA!


3. Can I use this DNA as a sample for gel electrophoresis?

Yes, but all you will see is a smear. The DNA you have extracted is genomic, meaning that you have the entire collection of DNA from each cell. Unless you cut the DNA with restriction enzymes, it is too long and stringy to move through the pores of the gel; instead, all you will end up seeing is a smear.


4. Isn't the white, stringy stuff actually a mix of DNA and RNA?

That's exactly right! The procedure for DNA extraction is really a procedure for nucleic acid extraction. However, much of the RNA is cut by ribonucleases (enzymes that cut RNA) that are released when the cells are broken open.

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