Extracting DNA from fruits

Do you know what DNA looks like? Grab some strawberries or bananas and find out!

The Experiment

Materials:

A medium banana or 3-4 strawberries
half a cup of water
1 tsp salt
dishwashing soap
rubbing (isopropyl) alcohol
ziploc bag
coffee filter
a small cup or narrow container
a wooden coffee stirrer or skewer

Try it out:

1. Put the rubbing alcohol in the fridge or freezer. It's important for it to stay cold.
2. peel the banana or remove the stems from the strawberries. Put the fruit in the ziploc bag.
3. add the water and salt, then close the bag. Mash the fruit until there are no lumps (Careful not to break open the bag!)
4. Once the fruit is mashed, squirt about a teaspoon of dishwashing detergent in the bag. Mix gently (you don't want too many bubbles)
5. Place the coffee filter on your cup or container and tape it around the edges so it doesn't fall in.
6. Carefully pour the mush in your ziploc bag into the coffee filter. Once all of the mixture has gone through, remove the filter paper.
7. Take your rubbing alcohol out of the fridge and slowly pour it down the side of the container so that there is a 1 or 2 inch layer of alcohol on top of the fruit mush.
8. Let the mixture sit for 7-10 minutes.
9. carefully put your coffee stirrer into the alcohol layer and swirl it gently. When you pull the stick out, you should see clear stringy stuff sticking to it. That's DNA!

What's happening

All plant cells have a cell wall and cell membrane on the outside and a nucleus on the inside. The nucleus is where the DNA is.



DNA is full of instructions, or genes, that tell your cells how to grow and what to do. Since it is so important, it is protected by the nucleus, cell membrane, and cell wall so that it doesn't get damaged.

So how did we get the DNA out of cell?

The first thing we did was mash up the fruit. This helps break up the cell wall. The dishwashing detergent also breaks up the cell wall, cell membrane, and nucleus.

The salt gives the DNA something to hold on to when everything else is breaking apart. When the salt and the DNA are together, the DNA doesn't like being in water anymore. When you add the alcohol, the DNA leaves the water and floats into the alcohol. This is what helps you see and pick up the DNA.

So would this experiment work with leaves in your garden? The answer is yes, it would work, but you wouldn't be able to see the DNA. Fruits like strawberries are good for this experiment because they have 8 copies of DNA! Most types of cells only have 2 copies, so they are a lot harder to see. You can try this out with other fruits and vegetables and see what happens.

If you thought this was cool...

This experiment is related to bioengineering. You can find out more here.
You can learn more about DNA and how it works by learning biochemistry or genetics.