Extracting
DNA from an
onion is an easy
experiment to do, especially for the
mad scientist on a budget. Why an onion? Onion
tissue is very
watery, and therefore disrupting
cellular membranes is quite easy. In order to
extract DNA, which is in the
nucleus, you have to break the
cell wall, the
cell membrane and the
nuclear membrane. The high water content makes it easier to do this. Onions don't have
chloroplasts or
starch, being a
root vegetable. Onions also have a surprising amount of DNA contained within each
cell. Onions are
polyploid, where as humans are
diploid. Combine these factors and you have some
ready to extract Deoxyribonucleic Acid. Then it is just a matter of time before your
hideous Onion soldiers have the
UN at its
knees!
Now, on to the experiment!
Materials:
5
cm3 liquid detergent
1.5
g of
table salt
50 cm3
water
One small
onion
A
Beaker
A
Funnel
A Pan of
hot water
A Pan of
ice cold water
A
Blender
A
Paper Coffee Filter
1 drop of
Protease Enzyme (
scientific supply catalogue time!)
10 cm3 of
Isopropanol
A small transparent container with a
lid
A sharp
knife
Step 1:
Add the table salt to the liquid detergent. Add the water to the salt-soap
solution. Stir well until all the salt is dissolved. This all goes in the
beaker.
Step 2:
Peel the onion and remove the top and bottom portions. Throw them out.
Chop the onion into small pieces and add them to the salt-soap solution. This solution is breaking down the cell membranes and
releasing DNA from the
nucleus inside each cell. The soap is attracting all the
lipids, and in turn disrupting the cellular membranes. The salt is preventing the DNA from
attaching to
freed sugars and
proteins.
Step 3:
Place the onion
solution beaker in the pan of hot water (at least 50
C, no more than 60C) for
15 minutes. The heat from the water speeds up the reactions that are breaking up the cells. The cells in the solution are in
self-destruct mode. Natural
enzymes which were released when the onion was chopped are now
reactive, and are attacking the cells
contents. The heat in the water bath helps promote the
endothermic reactions.
Step 4:
After the fifteen minutes, cool the beaker off with the pan of ice water. Be careful switching the beaker. Extreme temperature changes can
break glass. If the beaker is left in the
hot water for too long the DNA will dissolve, so the cooling bath is important. The enzymes are rendered
non-reactive by the decrease in temperature.
Step 5:
Pour the solution into the
blender and blend for no more than
5 seconds. The blender helps to break open the onion
cells, but more than 5 seconds will damage the DNA.
Clean the beaker.
Step 6:
Using the
funnel and the
filter paper, filter the onion solution back into the cleaned
beaker. This separates the
cell wall material from the DNA and
proteins, which are now in the beaker.
Step 7:
Take the small container and add about 10 cm3 of the onion
extract. Then add 1 drop of
Protease Enzyme. Seal the bottle and shake one or twice to
mix. Protease is a chemical that breaks down
proteins. Only a small amount is needed.
Step 8:
Very carefully pour 10 cm3 of
isopropanol onto the
surface of the onion extract.
Step 9:
Watch carefully. The DNA, which doesn't dissolve in the alcohol, rises to the
upper layer. Everything else
precipitates down. It looks like thin white
fibres of
cotton. This is the DNA with some sugars and proteins attached.
Optional 10th Step:
Use the DNA to create your
atomic supermen and
terrorise the free world.