Experiment: DNA Extraction from Fruit

Materials required
For this experiment you will need:- Fruit – Kiwi, Strawberries, and Banana all work well
- 5 g washing up liquid
- 2 g salt
- 100 ml tap water
- 100 ml of ice cold alcohol (isopropyl alcohol can usually be found at the pharmacists); put in a freezer for at least 30 mins before starting the experiment
- Access to hot water – about 60 °C
- Sieve or coffee filter paper
- Two glass beakers (or old jam-jars)
- Several bowls of different sizes, including a large bowl for making a water bath
- A paperclip
- Safety spectacles – if desired
Experiment to purify DNA from fruit
Step 1: Mash up the fruit of your choice in a bowl. Bananas, kiwis and strawberries all work well. (Remove the skin of the bananas and kiwi, we just want the insides!)Step 2: In a separate bowl, mix the washing up liquid, salt and tap water. Stir gently trying to avoid making too many bubbles in the mixture. This is your extraction buffer.Step 3: Add the fruit to the extraction buffer and mix again. Mash your fruit sample as much as you can, but again, try to avoid making too many bubbles.Step 4: Make a water bath with a temperature of about 60 °C. (A large washing up bowl works well for this.) Leave the fruit extraction mixture to incubate for 15 minutes.Step 5: After 15 minutes, filter your fruit mixture through a fine sieve or coffee filter. This will remove all the solid material that you don’t want. You should be left with a clear(ish) liquid.Step 6: Take the ice cold alcohol and very slowly, drop by drop, pour it down the inside of the container with your fruit mixture. What you want to do is produce a layer of the alcohol floating on top of the fruit mixture.Step 7: At the interface between the alcohol and the fruit mixture, you should see a white cloud-like substance forming. Use a hook (a bent paperclip would work) to slowly draw the DNA up and out of the solution.
Questions to think about
- Look at each step of the protocol. What are the different steps and reagents (washing-up liquid, salt, water, alcohol) used for in the experiment?
- How are you able to see the DNA?
- Do you think that the sample you have prepared is “pure DNA”?
If you have the opportunity to conduct this experiment, feel free to post comments about what you observe.
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