Extracting DNA – a classroom experiment
You can extract DNA in your classroom from a piece of fruit or vegetable – peas, onions and bananas usually work pretty well. Follow the instructions below … the way in which scientists extract bacterial DNA is slightly different, but it uses the same principles (cell wall disruption, salty environment, protein breakdown and alcohol precipitation) …
- Banana DNA (left) and bacterial DNA from a sediment sample (right). Both have been beaten to release DNA from cells, prepared in a salty environment, had their proteins removed, and have been precipitated in alcohol. Photos: Bonnie Laverock.
Step 1: Dissolve 3 grams of salt in about 100 millilitres of warm water (distilled water is best if you have access to a lab).
Why? The salt provides a “good environment” for the DNA so that it is more likely that the DNA will come out of the cells and into solution (DNA is negatively charged, and salt is positively charged)
Step 2: Add a mashed up banana to a food blender, pour the salty water over the top, and blend for 5 to 10 seconds. Pour through a sieve into a glass.
Why? The blender helps to break open the cells which contain the DNA.
Step 3: Add 2 to 3 teaspoons of normal washing-up liquid and stir gently (we don’t want bubbles!).
Why? Washing-up liquid works by breaking up the fat and grease stuck to our dishes. We have fatty molecules in our body – they are called lipids, and they hold cells together. The washing-up liquid helps to break open cells by attacking these lipids – this releases the DNA from the cells.
Optional extra step: If you want, you can also add pineapple juice to your mixture!