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.
   

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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