How to extract DNA in your kitchen

TV cop shows have made DNA extraction glamorous – with just a tuft of hair or speck of blood, crime scene investigators can isolate the genetic fingerprint of the ‘perp’ and bring them to justice. So you may be surprised to learn that DNA can be extracted from organic material in the kitchen, with just a few household ingredients.

You will need

• Safety glasses
• A small handful of strawberries (broccoli, peeled kiwi fruit, spinach or split peas will also work well)
• Food blender
• Sieve
• Bowl
• Tall glass or test tube
• Salt
• Washing-up liquid
• Pineapple juice
• Methylated spirit (meths)
• Ice or a freezer
• Toothpick, tweezers or small skewer
• A large pipette or
• turkey baster

SAFETY NOTES

Wear safety glasses when using methylated spirit. Do not drink methylated spirit. Keep fingers away from sharp blades on kitchen equipment.

Instructions

1. Put a handful of strawberries in a blender with half a cup of water and a pinch of salt. Blitz for at least 30 seconds until it achieves a smooth consistency.

   

2. Separate the tough, fibrous material by pouring the mixture through a fine sieve. Use the back of a spoon to squeeze all the juice through, leaving the cellulose behind.

   

3. Add a good squirt of washing-up liquid (about 30ml). Stir it and leave it for 5-10 minutes. Add a splash of pineapple juice.

   

4. Decant the (now undrinkable) strawberry juice into a tall glass or test tube. We did this with a turkey baster to avoid splashes.

   

5. Put on your safety glasses, and use a turkey baster to draw some ice-cold methylated spirits out of the bottle and trickle it down the side of the glass.

   

6. The meths will float on the surface. At the boundary of the two liquids, wispy threads will materialise. This is the strawberry’s DNA and can be plucked out.

   

What’s going on?

The washing-up liquid opens the fat-like membrane that makes up the walls of each strawberry cell’s nucleus, inside which the DNA is stored. The DNA is tightly coiled around specialised nuggets of packaging proteins, which need to be broken up before they can be extracted, and the pineapple juice contains a protein-digesting enzyme called bromelain which does this. Every DNA molecule is extremely long and is peppered with tiny positive and negative electrical charges, each of which is hugged by opposing tiny charges of the surrounding water molecules. The sodium and chlorine from the salt form a coat around the DNA, helping it clump together when mixed with alcohol.

The methylated spirit causes DNA molecules to separate from the mixture and ‘precipitate’ out as a solid mass. DNA is delicate, so the meths needs to be poured in carefully without stirring.

Read more:

• DIY Science: how to get electricity from coins
• DIY Science: how to create a bottled cloud
• DIY Science: how to make elephant toothpaste

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