Download 5 a day DNA

5 a day DNA
Please read this protocol fully and take note of the precautions on the back before beginning.
Apparatus
Ingredients
Chopping Board
Knife
Fork
1 l measuring jug
250 ml measuring jug
Tea-strainer/sieve
Teaspoon/medicine spoon
Tall glass/spice jars/champagne flutes
Paper clip
Fruit/vegetable
(Strawberries and onions work well – use red
onions if you can as they do not make you cry
as easily as white or brown onions.)
Liquid soap
(washing-up liquid and shampoo work well)
Methylated spirits
(put in freezer for 1 hour before use)
Optional:
Meat tenderising powder
(found in oriental supermarkets)
Table Salt (non-iodised type)
Hand-held blender
Bowl of cold water
Method
• Finely chop small amount of fruit and put
into the 1 l jug
(Around half a strawberry or 3 cm cube of
onion)
• Add 100 ml of water
• Crush mixture with fork or whizz with
hand-held blender
• Add 1 tsp detergent
• Add 1 tsp salt
• Stir gently
Optional:
[It is harder to extract DNA from some fruits and
vegetables. Before continuing, you may need to follow
these steps if you don’t get DNA the first time:
•Add 1 tsp meat tenderiser
•Mix and stand for 10-15 min
•Chill mixture in a bowl of cold water for 5 min.]
• Pour the mixture through a tea-strainer into a jug
• Pour a small quantity of the mixture into a tall glass
• Pour chilled methylated spirits carefully down the
side of the glass to a depth of about 3cm
• Small bubbles will appear and float up, pulling the strands of DNA out of the fruit mixture
• The DNA will form small wispy strands like cotton wool
• Use a paperclip (see back) to hook out the DNA
• You can store the DNA by drying it on a piece of dark cardboard, or putting it into a small amount
of methylated spirits in another spice jar
5 a day DNA
Paperclip hook
Take a paper clip and straighten it
Bend one end to form a small hook
Precautions
• Please note that the methylated spirits is highly flammable (keep away from flames),
and is poisonous – do not drink
• Some steps should be carried out by adults or under their supervision
• Please take care when handling sharp knives and the hand-held blender
• Do not drink any of the fruit/vegetable mixture or the methylated spirits
• Dispose of the solid waste in a bin and the liquid waste down the sink. Flush the sink with
copious amounts of water to dilute the methylated spirits
What is happening?
Depending on the type of tissue, the first step in DNA extraction is to break it up into small
pieces to increase the surface area that will be exposed to the chemicals at the next step.
This breaking up can be done by various means, but the simplest is chopping or blending.
The tissue is next mixed with water and detergent which help to dissolve the fats which
hold the cell membrane together.
Next, salt and meat tenderiser can be added if needed to help release the DNA. In cells,
DNA is bound to proteins. Salt causes all proteins to come out of solution and the meat
tenderiser contains proteases, enzymes that break up the proteins.
Several methods are available to isolate the DNA from the mixture, which draw on its
chemical nature. The simplest methods rely on how DNA reacts in a water-alcohol mixture.
In this experiment, we add methylated spirits (alcohol) so that it forms a layer on the
denser fruit/vegetable mixture (water). DNA doesn’t dissolve in alcohol, so as the water
and alcohol mix, the DNA comes out of solution. Some dissolved gas also forms bubbles on
the DNA and help pull it up to the surface.
This process is very similar to that used in the laboratory, except that scientists need to
get really pure DNA, so use more refined methods or kits to optimise the amount of DNA
extracted.
For more information, search the Internet for ‘DNA extraction’.