Pre Lab Questions
1. What do you think the DNA will look
like when extracted from a
2. Where is DNA found?
Is DNA in My Food???
• DNA is present in the cells of all living
• The process of extracting DNA from a
cell is the first step for many
laboratory procedures in
• The scientist must be able to separate
DNA from the unwanted substances
of the cell gently enough so that the
DNA does not denature (break up).
• Each cell contains 9 feet
• In an average meal, you
• This is equal to
miles of DNA
NUCLEUS with DNA
To Extract DNA, You Must
• Cell membrane
• Nuclear membrane
How Do I Begin?
• Place the strawberry in a zip lock bag
and remove the air
• Squash the berry with your hand to
begin the process
• Cell membranes are
made of phospholipids
• Phospholipids won’t
dissolve in water
• What do you use in
your home to remove
oils from your hands
or your dishes?
• SOAP or DETERGENT!
Soap & Detergent
• Soap gathers between oil
and water capturing the oil
in a bubble called a micelle
• When you wash your hands,
the soap carries the oils
• Dawn dishwashing works
BEST to remove
Soap & Detergent
• By adding a small amount
of table salt (NaCl) to
the soap solution, the
solution can punch holes
in the nuclear and cell
• The soapy solution also
helps removes proteins
Extracting the DNA
• The contents of the
proteins, etc.) must be
separated from the
• The larger cell parts
can be removed by
filtering the solid from
• To see DNA, it must be extracted or
“spooled” from the remaining liquid you
• DNA dissolves in water, but NOT in
• Adding COLD ALCOHOL will cause DNA
to precipitate (separate out) from the
Collecting the DNA
• The DNA will appear as
a white precipitate once
the alcohol is added
• HOLD THE TUBE by the
TOP, not the bottom so
the DNA strands won’t
fragment from the
heat of your hands!
1. Match the procedure to the purpose
A. Filter strawberry slurry through cheesecloth
B. Mush strawberry with salty/soapy solution
C. Initial smashing and grinding of strawberry
D. Addition of alcohol to filtered extract
___ To separate DNA from solution
___ Separate components of the cell
___ Break open the cells
___ Break up proteins and dissolve cell membranes
2. What did the DNA look like? Relate what you know about the
chemical structure of DNA to what you observed today.
3. Explain what happened in the final step when you added alcohol
to your strawberry extract.
4. A person cannot see a single cotton thread 100 feet away, but if
you wound thousands of threads together into a rope, it would
be visible much further away. Is this statement comparable to
our DNA extraction? Explain.
5. Why is it important for scientists to be able to remove DNA
from an organism? List two reasons.
6. Is there DNA in your food? ________ How do you know?