In this science experiment we will use forensic science to extract DNA from cheek cells.

SAFETY
• Wear goggles and gloves to prepare chemical recipes.
• Have children wear goggles and gloves to work with chemicals.

TIPS
• Have a stopwatch or clock with a minute hand handy. Have a waste container nearby for cups and
liquid waste.
• Place a beaker filled with rubbing alcohol at each group’s working space to keep the inoculating loops
or crochet hooks sterile for reuse.
• Use clear sports drink to see the precipitated DNA clearly.

MATERIALS
• Lysis solution
• Bottle for Lysis solution
• 5 test tube racks
• 5 250mL beakers (for alcohol)
• 5 400mL beakers (for ice)
• A cup, pipette, and resealable bag per student
• A graduated plastic test tube with screw cap per
student (purchase at an online or local science
supply store)
• 1 microcentrifuge tube per student (purchase at
an online or local science supply store)
• 1 inoculating loop or crochet hook per student (purchase
at an online or local science supply store)
• 1.5g (1/3tsp) table salt
• 10mL (2tsp) liquid soap (e.g. Woolite)
• 90mL (3fl .oz.) water
• Ethanol 95% (or 70% isopropyl alcohol)
• Clear sports drink (e.g. Gatorade)
• Ice
• Marker

RECIPE
Lysis solution
(Preparation time 5 min)
1 Mix 1.5g (1/3tsp) table salt with 10mL (2tsp) liquid soap and 90mL (3fl.oz.) water in a labeled bottle.

HOW TO PIPETTE
1 Fill a cup with water and place it on a table.
2 Squeeze the pipette bulb between index finger
and thumb.
3 Keep the bulb squeezed, and dip the pipette tip
into the water.
4 Release the pressure on the bulb to draw water
up into the pipette.
5 Position the tip of the pipette just above the
mouth of another cup.
6 Squeeze the bulb gently to squirt drops out of
the pipette.
7 Squeeze the bulb quickly to squirt water out of
the pipette.


Process For DNA Extraction Experiment

1 For each student: Before class begins, fill the
small bags with 2-3mL (1/2tsp) lysis solution. Fill
each cup with 5mL (1tsp) sports drink. Fill the
microcentrifuge tubes with 1mL (about 1/2 full)
ethanol. For each group: Fill the 250mL beaker
1/2 full of ethanol. Fill the 400mL beaker 1/3 full
of ice. Place the beaker with ethanol inside the
beaker of ice.

2 Divide the class into five groups. Hand each
group one test tube rack. Hand each student
one graduated test tube with screw cap. Instruct
the students to use the marker to label their test
tubes with their initials.

3 Give each student a small cup of the sports
drink. Instruct the students to take a sip, swish
the drink for one minute (timed on your stopwatch),
and scrape their cheeks with their teeth
gently and continuously to help release the
cheek cells.

4 Tell the students to spit the drink (with the collected
cheek cells) back into the small cup. Have
the students pour the cup’s contents into their
labeled test tube and discard the cup. Instruct the
students to place their test tubes in the rack.

5 Tilt a test tube at an angle to add a bag of lysis
solution to demonstrate to the students to do
the same with their test tubes.

6 Instruct the students to cap and gently invert
their test tubes 5-8 times to mix the solution,
place the tubes in their rack, and let stand for
two minutes (timed on your stopwatch).

7 Hand each student a pipette and each group
one beaker of ethanol on ice. Instruct the students
to hold their test tube at an angle and to
use the pipettes to add the cold alcohol down
the inside wall of the test tube until the total
volume reaches the 12mL line (there should be
two distinct layers). DO NOT shake the tubes to
mix the two layers together!

8 Instruct the students to place their test tubes
in the racks to stand for 15 minutes. Encourage
the students to watch as translucent DNA
strands begin to clump where the alcohol layer
meets the cheek cell solution.

9 After 15 minutes, hand each student one microcentrifuge
tube and one inoculating loop.
Instruct the students to scoop out their DNA
from the test tube and transfer it into the microcentrifuge
tube.

EXPLANATION
DNA is in all body cells except blood cells (the
DNA-containing nuclei of blood cells squeeze out
of the cell when they mature). Lysing, or breaking
open the cells and precipitating the DNA from the
nucleus, extracts DNA. The lysis solution contains
soap that breaks apart the cell membranes, and salt
that increases the osmotic pressure to help break
the membranes. The Gatorade or sports drink helps
maintain the electrolytes and pH environment the
DNA needs. The cold alcohol causes the DNA to
precipitate, or extract from the solution. Each individual
has a specific DNA sequence. In forensic
science, scientists use DNA to help identify suspects
and victims. Now go do the DNA extraction experiment with your friends!
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