DNA Detective Lesson Plan
Amount of time Demo takes:
5-7min
Materials :
1. Jug for water (suitable for drinking)
2. Bucket for waste
3. gloves (to handle people’s spit)
4. large container of salt
5. dawn dishwashing soap
6. small cups, 40/hr
7. paper clips 40/hr
8. trash bag
9. paper towels
10. disinfectant spray or antibacterial wipes
(to clean spills with)
11. Sodium Chloride solution(a.k.a. NaCl or
Table Salt), 8.0% (1mL/each)
12. Ethanol, 95% (5mL/each)
13. Dish Detergent Solution, 25% (1mL/each)
14. Test Tube, 16x100mm (6)
15. Test Tube, 13x100mm (6)
16. Corks, #__ & #2 (sized to fit each of the
above test tubes (2 TOTAL/each)
17. Test Tube Racks
18. Glass Stirring Rod or use paper clips
19. Source of clean drinking water
20. String
21. Markers
Set up instructions:
1. Prior to the event make dish detergent solution, heat the appropriate ratio of
soap to water on a stove (does not need to come to a boil). 1 part soap to 3 parts
distilled water. Pour solution into DNA Soap Solution container.
2. Prior to event make NaCl solution, 2 tbs salt to 3 cups of distilled water. Fill
Salt Solution container.
3. Prior to event, make sure there is enough Ethanol, purchase more from Chem
supply store on campus.
4. Prior to event, cut a set of necklace length string to use to tie on to vials for
participants to wear their DNA.
5. At event fill small nalgene dropper bottles with each solution for participants
to use, keep full.
6. Set out string, small vials, name tags and pens for participants to label their
DNA.
7. Fill drinking water jug, and locate the nearest faucet to refill water jug. Keep
jug clean please. :)
8. Clean vials between each group of people and set up between each group you
do the demonstration with.
SAFETY!
1.Biohazard, human saliva.
2.Precautions: Wear gloves when handling cups and when cleaning, keep station
clean with antibacterial wipes, have participants handle their own waste and
throw cup in trash bag.
Lesson’s big idea
● This experiment shows how to isolate human DNA from the cells of your
cheek. A series of reagents will be used to separate the DNA from the cells. This
procedure teaches the properties of cells, cell membranes, and deoxyribonucleic
acid (DNA).
Background Information
1. Dead cells are continually being sloughed off on both the inside and outside of
the body. Recently sloughed cells still contain their nucleus and their DNA
genetic material. This DNA can be collected and traced to a specific individual.
2. Detergents dissolve and break down the lipids (fats) and proteins that form
the primary cell membrane and disrupt the bonds that hold the membrane
together. The cell contents, including the nucleus, are thus released and become
available for further treatment or isolation. Sodium lauryl sulfate is an active
ingredient in detergents.
3. The final step of this experiment requires alcohol. The dissolved DNA will
precipitate when it comes in contact with the alcohol because it is not very
soluble in alcohol. If the procedure is done properly, fine, long strands of DNA
will form at the interface where the dissolved DNA and alcohol comes in contact.
It can then be easily spooled onto a glass stir rod.
Instructional Procedure
A. Obtaining the cheek cells
1. Take a small drink of water from a nearby drinking fountain and swirl it around
in your mouth several times (without swallowing) and then spit the water into
the cup. 30 seconds
2.Pour approximately 2 ml of the water containing dead cells into a large test
tube and place the test tubes in the test tube rack.
3. Add 20 drops (1mL) of the 8% NaCl (aq) to the larger test tube.
B. Releasing the DNA from inside the cheek cells
In this step, the cell membranes will be removed from the cheek cells using dish
detergent. The dish detergent breaks down the cell and nuclear membranes and
releases the DNA into the salt solution.
1. Add 20 drops (1mL) of the 25% liquid dishwashing detergent solution to the
“cheek” mixture in the large test tube.
2. Stopper the test tube and mix the contents of the tube by gently inverting the
test tube several times. Do not shake the test tube.
C. Precipitate the DNA
1. Holding the test tube at a slight angle, carefully add 5mL (100 drops) of 95%
ethanol down the side of the test tube so it forms a layer over the cheek mixture
in the test tube.
2. Place the test tube in the test tube rack for one minute and observe what
happens at the interface between the ethanol and the cheek solution. * The
dissolved DNA strands will precipitate when it comes in contact with the alcohol
because it is not soluble in alcohol.
D. Collect the DNA
1. Add 20 drops (1mL) of 95% ethanol to the smaller test tube.
2. Place a clean glass stirring rod (or paper clip) in the test tube containing the
DNA. Collect the DNA by winding it on the rod by turning the rod in one
direction.
3. Carefully remove the rod and DNA from the solution and transfer it to a small
vial containing approximately 1mL of 95% ethanol. Observe the DNA strands
floating in the alcohol.
4. Label your DNA sticker, tie a string around the top of your vial, put the sticker
over the string to help keep the string on and wear it! Sticker labels should be
placed high up on the vial and students should be encouraged to NOT open their
vials, or throw them away if they do not wish to keep them. Tell them to
not drink the contents of the vial, ethanol is bad for you.
Assessment:
1. How would you describe your DNA?
2. Did it look like what you would have expected?
3. What kind of jobs work with DNA?
4. Do identical twins have the same DNA?
Clean Up
Clean up between demonstrations if needed. When completely finished gather
all materials listed for this demonstration and make sure everything is accounted
for. If something was used up, broken or damaged. Let someone know so it can
get replaced or fixed. Check the supply of pre-prepared liquids, salt water and
soap solution, do more need to be made? Disinfect all items in this kit, this demo
involves a human bio hazard saliva.
References:
1. David A. Katz, Cladwyne, PA
2. Flinn Scientific Inc., “DNA Isolation Using Human Cheek Cells”, BioFax
#013101, Batavia, IL, 1999
3. MSDS for 95% ethanol
http://www.carolina.com/text/teacherresources/MSDS/ethanol95.pdf
National Standards: HSLS1
.