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Activity

DNA

Summary: 
Extract your own DNA from your cheek cells. Display it in a small tube.
Science content (2016 curriculum): 
Biology: Features, Adaptations of Living Things (K, 1, 3, 7)
Biology: Classification of Living Things, Biodiversity (1, 3)
Biology: Evolution, Natural Selection (7)
Chemistry: Atoms, Molecules (3-7)
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Materials: 
  • Dixie cups, one per person
  • Drinking water (5ml/1 tspn per person in the dixie cup)
  • 50ml tubes and caps, one per person
  • Salt water (1ml per person in their tube). Make 6% with ½ tspn salt in 4 tbspns water
  • Detergent (1ml per person). 7% SDS in water works best. 50% dish soap second best
  • Detergent aliquoted into eppendorf tubes, one each
  • Trays for tubes (1 per table)
  • 95% ethanol (5ml per person in a tube) - denatured ethanol from the hardware store is fine (95% ethyl alchol/5% methyl alcohol)
  • Bent funnel (see image), or hold the spout of a straight funnel against the side of the tube while pouring
  • Magnifier each (optional)
  • Black acrylic sticks, one per person
  • Small tubes to put DNA in, filled with ethanol
  • Pipette to rescue DNA
  • necklace string to hang DNA tubes on, one per student. About 70cm long fits over heads.
Procedure: 

You will collect DNA from your cheek cells.
You could get it from almost any cell in your body, as almost all your cells contain DNA.
There is even DNA in the root of a hair, or in cells left with a fingerprint, which can be collected for forensic investigations.
Cheek cells are the safest and easiest place to get it.

Collect cheek cells
1. Swish 5ml of water in your mouth for about 30 seconds, then spit it back into a cup.
2. Pour this mouthwash into a 50ml tube containing 1ml of 6% salt solution.
The swishing washes cells from the inside of your cheeks into the water. More vigorous swishing washes more cells off and yields more DNA. You collect hundreds of thousands of cheek cells in one mouth wash.
You are also washing bacterial cells from the inside of the mouth, so will isolate their DNA as well.
The salt solution is needed for the precipitation step later.

Break open the cells
3. Pour or pump 1ml of SDS solution to the mouthwash and salt solution.
4. Cap the tube, and mix the contents by gently inverting several times.
The detergent removes the greasy cell membranes from around the cheek cells (and bacterial cells).
The cheek cells also have a membrane around the nucleus, which is also removed.
The cell molecules (including the DNA) are released into the salt solution.

Collect the DNA.
5. Remove the cap. Rest a bent funnel in the tube (see image)
6. Pour 5ml of 95% ethanol into the funnel. The ethanol will run down the side of the tube, and makes a layer over the cell molecule/salt solution.
7. Hold the tube still for 30 seconds.
8. Look for the cloud of white, cottony strands of DNA forming in the lower half of the ethanol layer. There will probably be bubbles stuck among the strands, so if you do not see any DNA, first look for the bubbles. After a couple of minutes the DNA clump may float to the top of the ethanol layer.
Students can use a magnifier to look for the DNA forming - it gives a focus during the wait.
DNA is not soluble in ethanol, so it precipitates where the ethanol layer meets the cell molecule/salt solution layer. The salt from step 2 aids in precipitating the DNA. Most other cell molecules remain in solution.
The bubbles form as dissolved gas in the cell molecule/salt solution is forced out of solution by the ethanol.
Single DNA molecules are way too small to see - a strand seen here is a clump of thousands of DNA molecules.

Steps 9-12 should be done by the teacher or in small groups with close assistance
9. Locate the DNA in the tube. Hold the tube up close to your face, and move near to a light, so you can see
the DNA well.
10. Lower an acrylic stick into the tube, pushing it through the DNA clump, until it rests on the bottom of the tube.
11. Keep the stick resting on the bottom of the tube, and roll it between your fingers so that it spins in one direction. Do not spin it in both directions. Do not stir the stick in the tube, like you would stir a drink.
Keep spinning the stick in one direction until the DNA has wrapped around it.
If the DNA does not catch right away, repeat from step 10 with a new stick. The white DNA strands should
be visible on the black acrylic stick. They will look like a white goop.
12. Shake the DNA off into a small tube filled with 95% ethanol, scraping the stick on the side of the tube
if necessary.
If the DNA will not catch on the stick, use a pipette or eye dropper to suck it up. Avoid sucking up any of the salt layer, as the DNA will go back into solution.
Do not reuse sticks. They will not grab into the DNA again.
Different people get different amounts of DNA because some peoples’ cheek cells fall off more easily than others. If you get no DNA, make sure you swish really well when you try again.

Hang your DNA on a necklace
13. Thread the DNA tube onto a necklace string and tie securely. Students might instead make bracelets or a backpack memento.

The DNA should keep indefinitely in the small tube of ethanol. If the level of ethanol falls, top it up with some more.
The DNA you get is not pure DNA - there is also some protein mixed in. The long strands you see are clumps of DNA molecules. The protein is stuck to these strands and makes them a little whiter (and more bulky) than pure DNA.

More information

All living things contain DNA. You can adapt the above protocol to collect DNA from an onion, kiwi, or other fruit and vegetables:
Chop up the fruit or vegetable roughly. Drop it in a blender and add a cup of 6% salt solution. Blend for about 10 seconds. Drape several layers of cheesecloth over a cup. Pour the blended mixture onto the cheesecloth. Take a teaspoon of the liquid the drips through (which contains fruit/vegetable cells), and start at step 2.
You should get a lot more DNA than from your cheek cells, because you are starting with so many more fruit/vegetable cells.
For some fruits/veg it will be very hard to catch the DNA with a stick.

Attached documents: 
Notes: 

Have not found a source of black acrylic rods in Vancouver. Clear ones available from http://www.associatedplastics.com/contact.php Get 1/16 inch diameter.
Transport a class of necklace strings in egg boxes to prevent them from tangling together.

Grades taught: 
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7
Teacher: 
Alane Lublow
Barbara Duncan
Becky Evermon
Daphne Gurney
Donna Greening
Heather Wallace
Ingrid
Jane Kemp
Miles Patrick
Nina Hooker
Patricia Ellis
Romy Cooper
Scott Malin
Sharon Ghuman
Stephanie Monaghan
Taz Ismail
Teaching site: 
American Museum of Natural History
Beaty Biodiversity Museum
General Gordon Elementary
General Gordon Elementary Science Club
Horse riding stables, Richmond
ingridscience afterschool
Laurier Elementary
New York Hall of Science
ProD for Elementary teachers
After School Program at Elementary schools in New York City
Tyee Elementary
Activity originally developed and delivered: 

New York Hall of Science