What makes a banana a banana? Why does the plant only ever make bananas and not a whole fruit salad? Is a banana really a berry and is the plant it comes from really a herb, not a tree?! Well, it turns out that there is a code inside the banana that keeps instructions on exactly what the plant should make, what the berry should taste like and just how slippy the peel should be. Let’s see if we can extract the DNA from a banana!
A Banana for Scale
Okay, so there’s a lot more to bananas than just eating them… Bananas have been used to represent radiation doses, to measure things and they have featured in almost every cartoon ever.
The Banana Code
The code in the banana is DNA. It’s in all of us. You can find out more about DNA and how we might be able to change it one day here. There is a professional DNA research scientist on the Hopefully Nothing Goes Boom team so maybe I’ll talk her into writing about the DNA of dog poo one day…. seriously.
For now, we need an experiment for the Christmas table. Show off your abilities to reveal the hidden banana code… in the form of some lumpy grey mush. This experiment is cool, but not visually that exciting.
What you will need
- A banana
- Half a cup of warm water
- A teaspoon of salt
- A teaspoon of washing up liquid
- A sealable sandwich bag
- A coffee filter
- A funnel
- A long thin container
- Some ice cold isopropyl alcohol (rubbing alcohol)
How to extract banana DNA
Put your isopropyl alcohol in the freezer.
Mush up half the banana in the sandwich bag, get rid of the lumps.
Dissolve the salt in the water and pour it carefully into the bag. Mix it all about quite thoroughly.
Gently add in the washing up liquid and mix again but really gently. We don’t want to have a big frothy mess at this point!
Place your coffee filter into the funnel to support it. Put the funnel into your long thin container and then pour your lumpy yellow mess into your coffee filter.
Patience is a virtue…
Wait.
Wait some more.
Seriously, this is lumpy stuff trying to get through a coffee filter. This might take a while.
Wait a bit longer.
Take a spoon and lower it as close to the top surface of your filtered banana mush as you can. Gently pour the ice cold isoproyl alcohol down the spoon so that it forms a layer on top of the filtered banana soup.
2020 Edit: This is the same technique we use to make layered liquids like the brine column in this Global Science Show video.
Wait some more. This is an experiment that benefits from patience (that’s why I’m rubbish at it).
Forget “Junk” DNA – this is Gunk DNA
After a few minutes you should start to see some white (or grey) strands of blobby material start to float up from the interface of the banana soup up into the isopropyl alcohol. This, honestly, is DNA. You’ve messed about with the banana so much that you’ve bullied the DNA into leaving the water, it is no longer soluble. It instead wants to sit in the isopropyl alcohol but it doesn’t quite dissolve there either so instead it just blobs up into a goopy mess.
That really is the stuff that codes the banana into being exactly what it is – a tasty, slippy, radioactive measuring tape.
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