DNA Extraction Lab
Background
Whether you’re a human, rat, tomato or bacterium, each of your cells will have DNA
inside of it (with some rare exceptions, such as mature red blood cells in humans). Each cell has
an entire copy of the same set of instructions, and this set is called the genome. Scientists
study DNA for many reasons: They can figure out how the instructions stored in DNA help your
body to function properly. They can use DNA to make new medicines or genetically modify crops
to be resistant to insects. They can solve who is a suspect of a crime, and can even use ancient
DNA to reconstruct evolutionary histories!
To get the DNA from a cell, scientists typically rely on one of many DNA extraction kits
available from biotechnology companies. During a DNA extraction, a detergent will cause the cell
to pop open, or lyse, by breaking the phospholipid membranes of the cell and organelles,
releasing the DNA into the solution. Then alcohol added to the solution causes the DNA to
precipitate out. In this activity you will extract your own DNA from cheek cells, as well as the
DNA from various types of fruit. Strawberries are a good choice to use for DNA extraction
because they are octoploid, meaning that they have eight of each type of chromosome per cell.
Materials:
 Cup
 Stirring rod, toothpick, or inoculating loop
 Water
 Isopropyl alcohol
 Salt
 Dish Soap (detergent)
 Coffee filter
 Test tube
Cheek Cell DNA Extraction Procedure
1) As a class, mix 500 mL of water from the drinking fountain (use an empty water bottle)
with 1 Tablespoon of salt in a large cup.
2) Stir until the salt is dissolved.
3) Transfer 3 Tablespoons of the salt water mixture into your tiny Dixie cup.
4) Gargle the salt water (swish it in your mouth) for 1 minute. Your cheeks may get sore,
but don’t give up!
5) Spit the water back into your Dixie cup. Your cheek cells are now suspended in the
solution.
6) Over the sink, pour your cheek cell solution into a test tube.
7) Gently place one drop of soap into your test tube and swirl. Try to avoid making bubbles!
8) Pour ______ mL of COLD isopropyl alcohol gently into your tilted test tube so that it
forms a layer on top. (Sometimes adding food coloring to your alcohol solution makes the
next step easier to see.)
9) Wait about 2.5 minutes until you see white strands forming. This is your DNA!
10) Use a stirring rod or toothpicks to spool the strands of DNA out of the test tube and
into your micro-container.
Fruit DNA Extraction Procedure
1) The fruit DNA extraction buffer has been prepared for you: 900 mL distilled water, 50
mL dish soap, and 2 teaspoons of salt.
2) Smash a small piece of fruit on a glass dish and add 10 mL of the fruit DNA extraction
buffer.
3) Smash and mix the fruit and buffer for 1 minute.
4) Use a coffee filter to pour the fruit buffer mixture into a test tube so that only the
juice goes into the test tube. You will need a partner’s help for this step.
5) Throw away your coffee filter and fruit.
6) Slowly pour _____ mL of COLD isopropyl alcohol on top of the fruit juice mixture in the
test tube so that it sits on top.
7) White strands of DNA will precipitate in the ethanol layer. Use a stirring rod, tooth
pick, or inoculating loop to retrieve the DNA.
Discussion Questions
1. What does DNA look like?
2. Why is it important for scientists to be able to remove DNA from cells?
3. What is the role of detergent, ethanol, and salt in the extraction process?
4. Is there DNA in your food? How do you know? Why are you not harmed (or altered) by
injesting the DNA of another organism? What implication does this have for farmers who would
use GM (genetically modified) plants?