DIY DNA Extraction

D.I.Y DNA EXTRACTION


Precautions and safe working:
It is your responsibility to carry out a proper and sufficient risk assessment before conducting this experiment. The equipment and materials used are not particularly dangerous, but several are potentially hazardous.
Sharp: Blades.
Flammable: Ethanol.
Toxic: Ethanol - if swallowed.
What you will need:
Kiwi fruit (a ripe one works best)
Salt Solution
Washing up liquid (A supermarket own brand is perfect. The cheaper the better, as expensive brands have a lot of additives that interfere with the extraction)
Knife.
Chopping Board.
Measuring Jug.
Water Container – for beaker to sit in surrounded by water.
Beaker
Warm water (about 60oC).
Container of ice.
Ethanol
Test tube and holder
Paper clip or piece of fuse wire.
Funnel with Filter paper.

What to do:
• Put the bottle of Ethanol in the ice, to cool it down.
• In a beaker mix approx 2 grams of salt and 100mls of water or used supplied salt solution.
• Add 4 ml of washing up liquid, gently swirl to mix the contents, do not froth. Place the beaker in the bowl of warm water.
• Peel a kiwi fruit and coarsely chop it into small pieces. DO NOT reduce it to a mush. Scoop the pieces into the beaker with the water, salt and washing up liquid and gently mix the contents.
• Replace the beaker in the bowl of warm water and leave for 15 minutes.

• Filter the green mush into a test tube.
• Very carefully run the ice-cold ethanol down the inside of the test- tube onto the top of the green layer. Add about as much ethanol as there is green liquid; put the test tube into the holder and watch.

• Almost immediately you should see a fluffy white layer beginning to form at the boundary between the green and the purple liquids. This is the DNA that you have extracted from your Kiwi fruit. After a few minutes the DNA may float to the surface of the ethanol. The layer continues to grow for some time so have patience!
• It may be possible to scoop the DNA out of the liquid by using glass hook or a loop of wire, such as piece of bent fuse wire or a paper clip.

What is going on?
All the cells of the Kiwi fruit contain DNA. Slicing, chopping and blending the fruit breaks open many of the cells and allows the detergent/water/salt mixture to enter the cells and dissolve their contents, including the DNA. The salt helps dissolve the cell contents in the water, while the detergent helps breakdown the fatty membranes in the cells, making the extraction more efficient. The broken cells release three types of large molecule; the DNA; the proteins, which get eaten by the proteases in the kiwi fruit; and RNA, which is unstable and quickly falls apart in water.
The DNA molecule is very fragile so it is important not to 'blend' the fruit for too long, or shake the beaker too vigorously.
Filtering the juice removes large bits of debris.
Finally, DNA is not soluble in alcohol, so floating a layer of ice cold Ethanol over the solution of DNA causes the DNA at the interface between water and alcohol to come out of solution, where it becomes visible as fluffy white threads.


TEACHER POINTS:

- Laboratory Worksheet and Teacher Guide – including Technicians Requirements - of similar experiment is available at: http://www.ncbe.reading.ac.uk/NCBE/PROTOCOLS/plantdna.html

While this experiment demonstrates the chemistry behind DNA extraction it is not a practical method of obtaining DNA for use in further investigations. The identification of the white material as DNA is a matter of trust, which some children may find unsatisfactory.

The major value of this experiment is in demystifying DNA. “A recent study in the UK revealed that 40 percent of the population thought that only genetically engineered fruit contains DNA. It is not universally appreciated that DNA is in EVERY living thing” – Source http://www.chaosscience.org.uk/pub/public_html//article.php?story=20040206021823942 which is has another worksheet and recommended illustrated explanation of this experiment.

This experiment can easily be done in the home environment using simple kitchen equipment and common ingredients. It is recommended that using this as homework is considered for appropriate students. The “Kitchen Chemistry” version of this experiment provides three valuable outcomes.

1: Demystification of, and breaking down barriers to, science, and emphasis the ubiquity of DNA and natural biochemistry in the “real world”.
2: Simple success of apparently hard biochemistry
3: Home environment involvement in the science course

Two worksheets for this are:
- http://www.jic.ac.uk/corporate/search/print.asp?ref=http://www.jic.bbsrc.ac.uk/Corporate/media-and-public/diy-dna.htm
- http://www.york.ac.uk/res/sots/downloads/diydna.pdf


RESOURCE REQUIREMENTS:

Per Group -

Kiwi fruit (a ripe one works best)
50 g Salt (standard, pre-ground table salt works fine)
100 ml Washing up liquid (A supermarket own brand is perfect. The cheaper the better, as expensive brands have a lot of additives that interfere with the extraction)
Scalpel or knife
Chopping Board.
Measuring Cylinder
Small Container for water bath – and source of warm water (60C)
Beaker
Container of ice
500 ml Bottle of Ethanol (preferably precooled).
Test Tubes and Holders
Paper clip or piece of fuse wire.
Funnel with Filter paper.