INSTRUCTIONS:
Extracting DNA from human cells
METHOD:
1. Check that students are happy to
extract some of their own DNA.
It will be thrown away
afterwards so it won’t be used
for anything!
Ask them to put on gloves
and safety glasses.
2. Pour bottled water into clean cups
(just use enough water to cover the
bottom of the cup).
What’s needed?
o
o
o
o
o
o
o
o
o
o
o
o
o
Drinking water (bottled)
1 plastic cup (1 per student)
Stopwatch
¼ of a teaspoon of cooking salt
1 teaspoon or spatula (to add the
salt)
Dishwashing detergent
Pasteur pipette (to add the
detergent)
Tubes with lid (1 per participant)
Ethanol (that has been chilled on
ice)
Pieces of dark card
Safety glasses
Plastic gloves (various sizes)
Bucket for disposal (filled with
soapy water)
3. Ask students to gargle the water around
the mouth for 1 minute.
It helps if they chew their cheeks
and tongue gently.
Then ask them to slowly dribble the water back into cup.
4. Add quarter of a teaspoon of salt to the water and stir gently to
dissolve.
5. Put a drop of washing up liquid into the cup and stir or swirl tube gently.
6. Pour the sample into a tube.
7. Carefully pour the ethanol down the side of the tube using a pasteur
pipette so to not mix the two liquids. Pour enough alcohol to form a
layer about 2cm high.
8. DO NOT STIR TOO HARD. It might help to gently invert the tube.
Vigorous stirring can break up the DNA into small fragments, which will
make it harder to see.
9. Ask students to empty their tubes away at the end into a bucket of
soapy water.
What will you see?
The strands of thin DNA collect together to form webs of DNA in the ethanol.
Hold a piece of black card against the tube to make the DNA easier to see.
Why?
o The detergent breaks the cell open (it breaks apart the lipid bilayer in the cell
membrane and nuclear membrane) and the DNA will float out.
o As DNA is polar, it is soluble in water but not in ethanol.
Adding ethanol causes the DNA to precipitate out of solution, making it visible.
o The salt helps the DNA to precipitate.
o The precipitated DNA clumps together to form a white stringy mass which is
visible at the interface between the ethanol and the water.
o The alcohol will form a separate layer above the water because it is less dense.
INSTRUCTIONS:
Extracting DNA from Kiwis
METHOD:
1. Ask students to put on gloves
and safety glasses.
2. Ask them to take an ependorf tube
(and explain that experiments with
DNA tend to use small tubes as
dealing with small volumes).
3. Ask students to use a pasteur pipette to half
fill their small tube with kiwi solution.
What’s needed?
o
o
o
o
o
o
o
o
Kiwi solution (this contains
fruit chopped up and mixed
with salty, soapy water)
Pasteur pipette
1.5ml ependorf tubes
Ethanol (that has been
chilled on ice)
Pieces of dark card
Safety glasses
Plastic gloves (various
sizes)
Bucket for disposal (filled
with soapy water)
4. Then use a different pasteur
pipette to carefully pour the ethanol
down the side of the tube.
They should fill their tube to the top
(ie. 1:1 ratio of ethanol to kiwi solution).
5. DO NOT STIR TOO HARD. It might help to gently invert the tube.
Vigorous stirring can break up the DNA into small fragments, which will
make it harder to see.
6. Ask students to empty their tubes away at the end into the bucket of
soapy water.
Health and Safety
Take care when using ethanol. It is highly flammable and can be harmful if
ingested or if it comes in to contact with the skin.
What will you see?
The strands of thin DNA collect together to form webs of DNA in the ethanol.
Hold a piece of black card against the tube to make the DNA easier to see.
Why?
o The detergent breaks the cell open (it breaks apart the lipid bilayer in the cell
membrane and nuclear membrane) and the DNA will float out.
o As DNA is polar, it is soluble in water but not in ethanol.
Adding ethanol causes the DNA to precipitate out of solution, making it visible.
o The salt helps the DNA to precipitate.
o The precipitated DNA clumps together to form a white stringy mass which is
visible at the interface between the ethanol and the water.
o The alcohol will form a separate layer above the water because it is less dense.