Author: Benjamin Joslin
Date: 01-16-12
Experiment: See your DNA!
Age Range: 5-12 year olds
Time frame: 30 minutes
Goals
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To teach kids about the structure of DNA
To teach kids about the roles of DNA in living organisms
To teach kids the basic techniques of DNA extraction from plants and humans
o Basic chemistry behind the procedure
o Why scientists perform DNA extractions
Materials for DNA extraction (per student)
1. Safety glasses
2. Rubber gloves
3. 500 mL drinking water
4. 1 tablespoon of salt
5. 2 clear cups
6. 125 mL isopropyl alcohol USP 70%
7. Food coloring (optional)
8. 1 pipette
9. 1 drop of clear dishwashing detergent
10. 1 stir-stick
11. 1 toothpick
12. Small tube with top (Eppendorf tube) filled half way with isopropyl alcohol
Introduction
DNA – Stands for deoxyribonucleic acid. This molecule is the genetic instructions
used in the development and functioning of all living things.
Lyse – The death of a cell by bursting
Helix – The three dimensional shape, like that of a spiral staircase, of DNA
Teach students that all living organisms contain DNA by bringing in several
living and non-living things and asking which might contain DNA. Ask students
what they think DNA does. Demonstrate that DNA is the set of instructions that cells
use to produce the building blocks of life. Note how small, yet important, DNA is in
living organisms.
Procedure
Step 1: Add 1 tbsp of salt to cup of water and stir until the salt dissolves completely
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Step 2: Pour a little water into another cup and swish the water around in your
mouth for 30 seconds.
Step 3: Spit the water into the cup of salt water.
Step 4: Dip the stir-stick in the drop of dishwasher detergent and gently stir it in
the salt water cup two times.
Step 5: Add a drop of blue food coloring to the rubbing alcohol to help distinguish
between the alcohol and water. Optional.
Step 6: Holding the cup at an angle, carefully use a pipette to drop the alcohol down
the side of the cup. The blue alcohol should form another layer (approximately 2
cm) on top of the water. Be careful not to pour the water in too quickly.
Step 7: Watch the thin strands of DNA collect in the alcohol layer! Use a toothpick
or a stir-stick to collect the DNA strands.
Step 8: Place the DNA into the small tubes containing alcohol and have the students
label them to take home.
Optional Step: The students can also make jewelry with the tubes by adding a drop
of food coloring to their vial and closing it with a string attached.
Cleanup: Discard the contents of the cups and return the supplies to their proper
place.
What happened?
Cells from your body were removed by rubbing the toothpick against the
inside of your mouth. Placing these cells into a salt water solution helped mimic the
body’s natural conditions. The cells’ membrane and nucleus (where the DNA
resides within a cell) were lysed or opened by the addition of detergent. After
adding the alcohol, the free DNA migrated upwards and accumulated in this layer.
Slowly, as more DNA clumped together it becomes visible to the naked eye!
Supplemental Experiment
You can perform the same experiment with strawberries, and other fruits,
that may yield better results (more visible DNA) because strawberries are
octoploid, contain 8 sets of chromosomes compared to our 2. While the procedure
is roughly the same, a detailed overview of the experiment may be found here:
Strawberry DNA extraction, http://seplessons.ucsf.edu/node/217/, 01/05/12
References
Extract Your Own DNA, http://nature.ca/genome/05/051/pdfs/DNAextract_e.pdf,
01/05/12
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