DNA From a Banana

By Rebecca Hernandez

Here at the Null we've been turning the place upside down again with one of our mad experiments. Uh oh. But you know what? You can extract DNA from bananas using ingredients you'll find in your own kitchen. No laboratory necessary!

WHAT YOU'LL NEED:

bananas, or some other fruit or veg that is easy to mash up (peas work well too)
water
salt
coffee filter
funnel
clear plastic cups
washing up liquid/dish soap
pineapple juice
rubbing alcohol/surgical spirit

WHAT TO DO:

1. Dissolve about 1 gram of salt in 100 millilitres (ml) of water.

In terms of safety, there's actually no reason to wear latex gloves to dissolve salt in water. We just like wearing them. There's also no need to do this in a lab, but they wouldn't let us out.

2. Mash up about ½ banana (or about ½ cup peas) in the salt water to make a banana soup. Be sure it’s mashed up really well.

Mashing up the banana helps to break down the cell walls and will make DNA easier to extract. Salt helps DNA solidify later in the experiment.

3. Pour banana soup through a coffee filter into a new clear plastic cup. You'll only need about 5-10 ml for the rest of the experiment. Toss out coffee filter with banana bits (or save for banana bread!)

Cells need to be nice and mashed up before you can extract DNA. This is why we need to filter the clumpy bits through the coffee filter.

4. Add a few drops of washing up liquid to your banana soup. Swirl the mixture but do not shake - no bubbles!! (You can also do this with jazz hands).

Washing up liquid is made of grease, which is very similar to cell membranes. The grease will penetrate the membranes and break them up, allowing the DNA to escape from the nucleus.

5. Let mixture sit for about 5-10 minutes.

6. Add about 1-2 millilitres of pineapple juice. Stir GENTLY!

When you broke open the cell membrane with the detergent, not only did you release the DNA, you released lots of proteins in the cell too. Some of these proteins are attached to the DNA. Pineapple juice contains an enzyme which will break up those proteins and make the DNA unravel, making it easier to see.

7. Slowly pour rubbing alcohol into your cup until it forms a layer equal in volume to your banana soup mixture. The alcohol layer should sit on top of the soup mixture. Swirl mixture.

We use rubbing alcohol because it separates the DNA from the rest of the proteins and grease that are in the banana cells. DNA likes to be in alcohol, which is less dense than water—which is what grease and proteins prefer.

8. You should see some whitish stringy stuff at the bottom of your alcohol layer. You can use a wooden stick like a toothpick to ‘spool’ this out of the mixture. Congratulations, you’ve extracted DNA!

We messed about with the proportions of chemicals a bit and to our surprise produced this. We call him Harold.

FUN STUFF TO TRY

Try using different sources of DNA. You can try different types of fruit and veg (peas work great), and even meat (for example chicken liver) and eggs. Disclaimer: pleasant smells not guaranteed.
Do different types of detergent make a difference? What about trying shampoo, bubble bath, or even laundry detergent?
You can use a few different things for your enzyme source instead of pineapple juice. Contact lens solution, meat tenderizer, and other types of juices will work.
Be like a real scientist and make some mistakes! What if you forgot a step—will you still be able to extract your DNA? Try different volumes. Maybe more detergent works better.