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Notes from the field ·

Strawberry DNA Extraction: Pull DNA Out of a Fruit with Kitchen Supplies

By Ahmed, founder

It’s surprising how many students think DNA is something only a lab can show. Here’s an experiment that makes it visible with a strawberry, soap, salt and a little cold alcohol. You can see DNA, a cloudy white tangle, with your own eyes.

What you need

  • 1 or 2 strawberries (fresh, or frozen and thawed)
  • A zip-top freezer bag
  • 2 teaspoons of clear liquid dish soap
  • A pinch of table salt
  • About ½ cup of water
  • A coffee filter or cheesecloth, and a clear glass
  • Ice-cold rubbing alcohol (isopropyl, 70% or stronger), handled by the grown-up or teacher only

Put the alcohol in the freezer for an hour beforehand.

The method

  1. Put the strawberries in the bag, seal it and mash with your fingers for about two minutes.
  2. In a cup, mix the soap, salt and water. Add it to the bag and mash gently for another minute, trying not to make too many bubbles.
  3. Pour the mixture through the filter into a clear glass.
  4. A grown-up slowly tips ice-cold rubbing alcohol down the side of the glass so it forms a layer on top, about the same depth as the strawberry liquid.
  5. Wait a few minutes without moving it. White, cloudy strands rise into the alcohol layer. That’s DNA.

You can pick up the clumps with a toothpick or a wooden skewer (blunt end).

What each ingredient does

  • Mashing breaks cells apart physically.
  • Soap dissolves the fatty membranes around the cell and its nucleus, releasing the contents. Soap does to cell membranes what it does to grease on a plate.
  • Salt helps the DNA strands clump together.
  • Cold alcohol is the key. DNA doesn’t dissolve in alcohol, so it comes out of the liquid and becomes visible as a solid. It rises because the alcohol is less dense than the water.

Fair test idea

What happens if you leave out the soap? Do two bags, one with and one without. Compare how much DNA appears. It’s a good test of what the soap actually does.

Why strawberries?

Strawberries are a good choice: they’re soft and easy to mash, and ripe strawberries have eight copies of each chromosome (they’re octoploid), so there’s a lot of DNA per cell. Other fruit, such as bananas or kiwi, work too.

What you’re actually seeing

What looks like a single white strand is millions of long DNA molecules clumped together. Each one is invisible alone. DNA carries the instructions a cell uses to build and run an organism, and every living thing has it.

Safety

Rubbing alcohol is flammable and harmful if swallowed. A teacher or parent handles it, keeps it away from flames and eyes, and works with ventilation. Nobody eats or drinks from the experiment. Wash hands afterwards.

The classroom version is Can you pull DNA out of a strawberry? from Cells: The Smallest Living Things, which also asks How big is a cell? and How do things get in and out of a cell? Sign up for three lessons free.