Extraction of DNA from peas (In honor of Mendel)
Since DNA is the blueprint for life, everything living contains DNA. The isolation of DNA
is one of the most basic and essential techniques in the study of DNA. Extraction and purification of
DNA are the first steps in the analysis and manipulation of DNA that allow scientists to detect
genetic disorders, produce DNA fingerprints and even create genetically engineered organisms.
The first step will be to lyse (or break open the cell). This can be done by grinding the tissue in a
blender. After the cells have broken open, a salt solution and a detergent solution is added. These
solutions break down and emulsify the fat and proteins that make up the cell membrane. Finally
rubbing alcohol is added because DNA is soluble in water. The alcohol causes DNA to precipitate,
or settle out in solution, leaving behind all the cellular components that aren’t soluble in alcohol.
The DNA can be spooled (wound) on a stirring rod and pulled from the solution at this point.
Materials: Blender, green split peas, table salt, detergent containing SDS, water, measuring cup,
measuring spoons, strainer, meat tenderizer, rubbing alcohol, test tube (provided)
STEP 1: Place the following in a blender
• 1/2 cup of peas (100ml)
• 1/8 teaspoon table salt (less than 1ml)
• 1 cup cold water (200ml)
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.
STEP 2: Soapy Peas
Pour your thin pea-cell soup through a strainer into another container
(like a measuring cup).
Add 2 tablespoons liquid detergent (about 30ml) and swirl to
mix. (Dishwashing soap like Joy or Woolite works best)
Let the mixture sit for 5-10 minutes.
Pour the mixture into a test tube or other small glass
container, about 1/3 full.
STEP 3: The Power of Enzymes
Add a pinch of enzymes (use meat tenderizer for enzyme addition /pineaple
juice) to the test tube and stir gently. Be careful! If you stir too hard, you'll break
up the DNA, making it harder to see.
STEP 4: Alcohol Separation
Tilt your test tube and slowly pour rubbing alcohol (70-95% isopropyl) 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. 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.
DNA is a long, stringy molecule that likes to clump together.
YOU HAVE JUST COMPLETED DNA EXTRACTION!!!
IES ÁNXEL FOLE