Page 54 - BBC Knowledge - October 2017 IN

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Science
Experiments SAFETY
NOTES
Wear safety glasses when
using methylated spirit.
Do not drink methylated spirit.
EXTRACT Keep fingers away from sharp blades
on kitchen equipment.
DNA IN YOUR Wash hands after touching plants,
soil or animals.
KITCHEN Do not allow children to
visit a beach
unsupervised.
TV cop shows have made DNA extraction glamorous – with just a tuft of hair or speck of
YOU WILL NEED: blood, crime scene investigators can isolate the genetic fingerprint of the ‘perp’ and bring
l Safety glasses them to justice. So you may be surprised to learn that DNA can be extracted from organic
l A small handful of material in the kitchen, with just a few household ingredients.
strawberries (or broccoli,
peeled kiwi fruit, spinach
or split peas) WHAT’S GOING ON?
l Food blender The washing-up liquid opens the fat-like membrane that makes
l Sieve up the walls of each strawberry cell’s nucleus, inside which the
l Bowl DNA is stored. The DNA is tightly coiled around specialised
l Tall glass or test tube nuggets of packaging proteins, which need to be broken up
l Salt before they can be extracted, and the pineapple juice contains
l Washing-up liquid a protein-digesting enzyme called bromelain that does this.
l Pineapple juice Every DNA molecule is extremely long and is peppered with tiny
l Methylated spirit (meths) positive and negative electrical charges, each of which is hugged
l Ice or a freezer by opposing tiny charges of the surrounding water molecules.
l Toothpick, tweezers The sodium and chlorine from the salt form a coat around
or small skewer the DNA, helping it clump together when mixed with alcohol.
l A large pipette or The methylated spirit causes DNA molecules to separate from
turkey baster the mixture and ‘precipitate’ out as a solid mass. DNA is delicate,
so the meths needs to be poured in carefully without stirring.

METHOD:

1. Put a handful of strawberries in a blender 2. Separate the tough, fibrous material 3. Add a good squirt of washing-up
with half a cup of water and a pinch of salt. by pouring the mixture through a fine liquid (about 30ml). Stir it and leave
Blitz for at least 30 seconds until it achieves sieve. Use the back of a spoon to squeeze it for five to10 minutes. Add a splash of
a smooth consistency. all the juice through, leaving only the pineapple juice.
cellulose behind.

4. Decant the (now undrinkable) strawberry 5. Put on your safety glasses, and use 6. The meths will float on the surface. At the
juice into a tall glass or test tube. We did a turkey baster to draw some ice-cold boundary of the two liquids, wispy threads will
this with a turkey baster to avoid splashes. methylated spirits out of the bottle and trickle materialise. This is the strawberry’s DNA and
it down the side of the glass. can be plucked out (see right).
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OCTOBER 2017