Extracting DNA from Strawberries Experiment

Today in botany we extracted DNA from strawberries! This is a super-easy experiment with dramatic results.

You need the following supplies:

  • 10 ml (2 tsp) dishwashing liquid (or shampoo without conditioner) – shampoo frees the DNA by disrupting the cell membranes.
  • 90 ml (6 T) water
  • 15 grams ( or 1/4 tsp) of salt (Salt allows the DNA to precipitate because the positive Na+ ions shield the negative charges on the DNA.)
  • 1-2 fresh or frozen strawberries (We used strawberries because they are octoploid – which means they 8 copies of each type of chromosome. That means they have 8x time the DNA of normal cells. Strawberries also have enzymes like pectinase that assists in cell wall breakdown.)
  • Ziploc bag
  • Coffee filter
  • Clear glass or test tube
  • Cup or beaker or similar container
  • Isopropanol alcohol

Instructions:

  1. Put your strawberries in the Ziploc bag, close the bag and then mash them up for a couple of minutes.
  2. In a large container, mix the dishwashing liquid, water and salt.
  3. Pour 10 ml of the dishwashing liquid, water and salt mixture into the Ziploc and mix it with your mashed up strawberries for about a minute. *Note: We actually had to pour in more liquid to get our strawberry mash to liquify. Add as much as you need to make a juice like consistency.
  4. Pour the solution through a coffee filter into a clear glass or test tube. You’ll have more visible results if you can pour it into a skinny test tube, like we did.
  5. Now gently pour in Isopropanol alcohol on top of the filtered strawberry liquid. Pour in 2x the amount of the strawberry liquid. So, if you poured in 4 ml of strawberry “juice”, you should pour in 8 ml of alcohol on top. DO NOT MIX. Just pour it gently right on top of the strawberry “juice”.
  6. As you view the tube (or glass), you’ll see a fuzzy, stringy white precipitate start to bubble up and then gather in a mass as it floats to the top of the alcohol layer. If for any reason you don’t see this, just add a little more salt. This is the strawberry’s DNA! You can poke in a toothpick or other item and spool some of the DNA onto it.

Here’s a picture of our test tube with DNA floating up to the top of the alcohol layer. You can see it clumping up at the top of the liquid with some bubbles.

Here’s a close-up. I’ve circled areas with blue. Look at the lower circle. You can actually see thread-like strands of DNA floating up.

So how in the world can you see DNA when it’s so tiny inside a cell and we wouldn’t even be able to see it with our microscopes? Think of cotton threads. You wouldn’t be able to see a single thread from 100 feet away, but you would be able to see it if it was wound together into hundreds of feet of rope. That’s what happens when you extract the DNA from strawberries. You can’t normally see an individual strand of DNA. However, when it becomes spooled together with all of the other strands via the extraction process, it becomes visible – just like our thread analogy.

This is a great experiment not just for botany but also for biology or a human body study. I think Otter was impressed that he was looking at real DNA!