DNA, or deoxyribonucleic acid, contains all of the information needed to make every protein in a living thing and is sometimes called the “blueprint of life.”
This morning, on Kare11 Sunrise news, the kids and I showed viewers how easy it is to extract DNA from strawberries.
In higher organisms like plants and animals, DNA is stored in a compartment called a nucleus where the long, string-like DNA is tightly coiled. To separate DNA from the organism that contains it, you have to break the cells apart (lysis), filter out the big pieces of cell parts and collect the remaining liquid, or supernatent, and add chemicals like salt and alcohol to separate (precipitate) the DNA from the rest of the supernatent.
To extract DNA from strawberries at your own kitchen table, you’ll need: 3 strawberries, measuring spoons, 2 one or two-cup pyrex measuring cups, a cone-shaped coffee filter, a plastic zip-lock bag, small clear plastic or glass cups, laundry detergent (liquid or powdered), ice cubes, 2 big bowls, a timer, salt and ice-cold rubbing alcohol. *Always supervise children around cutting tools and alcohol.
Put the alcohol in the freezer at least an hour before you start the experiment so it gets cold enough to precipitate DNA. Make sure the bottle is well-labeled and you remove it when you are done since rubbing alcohol is poisonous if it is consumed by accident.
First, cut the strawberries into small pieces using a butter knife. Put the pieces in one of the pyrex measuring cups and mash them up well with a fork until you can’t see chunks any more.
Add a teaspoon of liquid or solid detergent to 1/2 cup of warm tap water, mix and pour this soapy mix over the strawberries. Fill one of the big bowls about half way with hot tap water (as hot as it comes from the faucet) and set the pyrex cup containing strawberries inside the bowl of warm water. Mix well with your fork. The detergent and warm temperature will start lysing (breaking up) the strawberry cells and proteins called enzymes will start chewing up cell parts, releasing the DNA from the nucleus. Wait 12 minutes, stirring the strawberry mixture once in a while.
Fill the other bowl about halfway with water and lots of ice cubes to make an “ice bath”. When the 12 minutes are up, set the cup containing the strawberry mixture into the ice bath for around 5 minutes, stirring once or twice. The cold temperature will slow the enzymes down so they don’t start chewing up the strawberry DNA.
While you wait, cut a plastic bag into a funnel the same size as your coffee filter and clip off the corner of the plastic bag so liquid can flow out (see photo). Put the coffee filter inside your plastic bag funnel and set the whole thing in your other pyrex measuring cup (or a wide glass.)
When the 5 minutes are up, pour the strawberry solution into the filter/funnel and hold it while the strawberry gunk is filtered out and the supernatent containing the DNA flow through and into the cup below. If your filter gets clogged, use a spoon to carefully remove some of the strawberry gunk so more liquid can flow through. Don’t worry if you don’t collect every drop.
Now you get to precipitate the DNA! Pour some supernatent into your small, clear glass until it is about 1/3 full. Add about 1/4 teaspoon salt to the supernatant and mix it up well with a spoon or knife. Now, gently pour an equal volume (the same amount as your supernatent) of ice-cold alcohol into your supernatent. Do not mix it, but put your hand over the top of the glass and rock it gently. Set it down on the table and let it sit for a few minutes.
You should see a cloudy goo forming near the top of the liquid. It may look bubbly or slightly white. This is strawberry DNA.
You can use a toothpick or plastic fork to gently lift the DNA from the glass. It will look like clear slime.
Put it on a plate and touch it… how does it feel?
Congratulation scientist! You’ve just extracted DNA from a living organism!
*If you don’t see DNA, make sure you’ve added the salt. You can also set the entire glass in the freezer for half an hour if your alcohol wasn’t cold enough and the DNA should precipitate out!