DNA Extraction
Materials:
Pineapple juice
AJAX detergent
Salt
Rubbing Alcohol
Strainer
Water
Strawberries
Saliva
Test tubes
Stirring rod or wooden stick or paper clip
Procedures:
Part A – Saliva
1. 1. Swish ½ cup salt solution around in your mouth for about 10 seconds.
2. Add about 2 tablespoons of liquid detergent (AJAX) and swirl to mix for 5 minutes. Let
the mixture sit for 5 minutes.
3. Pour the mixture into test tubes or other small glass containers, each about 1/3 full.
4. Add a splash of pineapple juice (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.
5. Tilt your test tube and slowly pour rubbing alcohol (70-95% 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 strawberry 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. DNA is a long, stringy molecule that likes to
clump together.
Part B - Strawberries
1. Put in a blender on high for 15 seconds:
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Your DNA source (about 100ml or ½ cup of strawberries)
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) The blender
separates the strawberry cells from each other, so you now have a really thin
strawberry-cell soup.
2. Pour your thin strawberry-cell soup through a strainer into another container (like a
measuring cup).
3. How much strawberry soup do you have? Add about 2 tablespoons of liquid detergent
(AJAX) and swirl to mix for 5 minutes. Let the mixture sit for 5 minutes.
4. Pour the mixture into test tubes or other small glass containers, each about 1/3 full.
5. Add a splash of pineapple juice (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.
6. Tilt your test tube and slowly pour rubbing alcohol (70-95% isopropyl or ethyl alcohol)
into the tube down the side so that it forms a layer on top of the strawberry mixture.
Pour until you have about the same amount of alcohol in the tube as strawberry mixture.
DNA will rise into the alcohol layer from the strawberry layer. You can use a stirring
rod, wooden stick or other hook to draw the DNA into the alcohol. DNA is a long,
stringy molecule that likes to clump together.
How did that work?
The extraction of DNA requires three easy ingredients:
Detergent - A cell's membranes have two layers of phospholipids with proteins going through
them. Both the cell membrane and nuclear membranes must be broken open in order to release
the DNA. When detergent comes close to the cell, it captures the lipids and proteins, and
thereby isolating the DNA.
eNzymes (pineapple juice) – helps to digest the proteins
Alcohol - 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?" 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.