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How to Extract DNA from Anything Living
DNA! You mean I can see it? How?
Frequently Asked
Questions
Just follow these 3 easy steps:
Detergent
1. I'm pretty sure I'm not
seeing DNA. What did I do
wrong?
eNzymes (meat tenderizer)
Alcohol
First, check one more time
for DNA. Look very closely at
It's that simple? Tell me more!
the alcohol layer for tiny
First, you need to find something that contains DNA. Since DNA is the blueprint for life,
bubbles. Often, clumps of
everything living contains DNA.
DNA are loosely attached to
the bubbles.
If you are sure you don't see
DNA, then the next step is to
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
make sure that you started
Here's the fun part. Put in a blender:
blended cell soup is too
•
•
•
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)
with enough DNA in the first
place. Many food sources of
DNA, such as grapes, also
contain a lot of water. If the
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
Blend on high for 15 seconds.
allowing enough time for
The blender separates the pea cells from each other, so you now have a really thin pea-
each step to complete. Make
cell soup.
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
And now, those 3 easy steps:
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
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.
long and stringy. Each cell of
your body contains six feet of
DNA, but it's only onemillionth 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
Try one of these detergents or whatever you have on hand.
cell.
Imagine this: the human
Why am I adding detergent?
body contains about 100
trillion cells, each of which
Blending separated the pea cells. But each cell is surrounded by a sack (the cell
contains six feet of DNA. If
membrane). DNA is found inside a second sack (the nucleus) within each cell. To see
you do the math, you'll find
the DNA, we have to break open these two sacks. We do this with detergent.
that our bodies contain more
Why detergent? How does detergent work?
Think about why you use soap to wash dishes or your hands. To remove grease and
dirt, right?
Soap molecules and grease molecules are made of two parts:
• Heads, which like water
• Tails, which hate water.
than a billion miles of DNA!
3. Can I use this DNA as a
sample for gel
electrophoresis?
Both soap and grease molecules organize themselves in bubbles (spheres) with their
Yes, but all you will see is a
heads outside to face the water and their tails inside to hide from the water.
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
When soap comes close to grease, their similar structures cause them to combine,
and RNA?
forming a greasy soapy ball.
A cell's membranes have two layers of lipid (fat) molecules with proteins going through
them.
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.
When detergent comes close to the cell, it captures the lipids and proteins.
Want to learn more?
Here are some books to try:
•
DNA Is Here to
Stay, by Dr. Fran
Balkwill. 1992. ISBN
# 0-00-191165-1
(Ages 9-15)
•
Amazing Schemes
within Your Genes,
by Dr. Fran Balkwill.
1993. ISBN # 000-196465-1 (Ages
2. Add a pinch of enzymes to each test tube and stir gently. Be careful! If you stir too
9-15)
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.
•
Double Talking
Helix Blues, by Joel
Herskowitz. 1993.
Book and cassette
Book and cassette
tape. ISBN # 087969-431-9 (Ages
8 and up)
•
Ingenious Genes, by
Patrick A. Baeuerle
and Norbert Landa.
3. Tilt your test tube and slowly pour rubbing alcohol (70-95% isopropyl or ethyl alcohol)
Barron's
into the tube down the side so that it forms a layer on top of the pea mixture. Pour until
Educational Series,
you have about the same amount of alcohol in the tube as pea mixture.
Inc., Hauppauge,
NY. 1997. ISBN #
0-7641-5063-4
(Ages 8-12).
•
How the Y Makes
the Guy, by Norbert
Landa and Patrick A.
Baeuerle. Barron's
Educational Series,
Inc., Hauppauge,
NY. 1997. ISBN #
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.
0-7641-5064-2
(Ages 8-12).
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. Some will
choose the couch, others might choose the rocking chair.
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.
©2004 University of Utah v2.1