DNA Extraction

 

The recipe for making DNA

Most people think that DNA is some kind of mysterious substance buried away in our cells never to be seen — but that is not the case. Here is a recipe for the extraction of DNA to make in your own kitchen — not unlike the type of experiment Rosalind Franklin would have performed in her lab at King’s college, London. She had in fact tried oranges which were not at all suited to this form of experiment and proved useless. Kiwi fruit is best suited to making DNA because of its structure.

You will need:

1. A ripe Kiwi fruit.
2. Table salt.
3. Non concentrated washing up liquid.
4. Knife and a chopping board.
5. Measuring scales.
6. A measuring jug.
7. A teaspoon (5 ml).
8. Small bowl.
9. A large sauce pan full of hot water (not boiling — about 60 degrees).
10. A large sauce pan full of ice.
11. Coffee filter and filter funnel.
12. A tall, thin plain glass.
13. Some thin wire (fuse wire).


What to do:

1. Put the bottle of methylated spirits in the ice.

2. Make up a solution of 3 grams of salt, 10 ml of washing up liquid and 100ml of water. Measure 3 grams of salt . You may find that your scales will weigh out a minimum of 25 grams. If this is the case add 80 ml of washing up liquid (16 measuring spoons) and make up to just less than one litre. Stir your mixture thoroughly (avoid froth) to dissolve the salt.

3. Peel and chop one Kiwi fruit. Scoop this into the small bowl and add 100 ml of the salt — detergent mix.

4. Put the bowl containing the mixture into the saucepan of hot water and leave for 15 minutes.

5. After 15 minutes pour the mixture into the coffee filter, and catch the liquid that filters through in the tall glass. You will need about one fifth of a glass.

6. Very carefully drizzle the ice cold meths down the inside of the glass so that it forms a purple layer on top of the green layer. When there is about a fifth of a glass of meths (i.e. two fifths including the green liquid) put the glass on the table and watch what happens.

7. After a few moments you should see a white layer beginning to form at the boundary between the green and the purple layers. If you have done it correctly you will see that the layer is made up of a filament — DNA from Kiwi fruit.

8. Try scooping the DNA out with a loop of thin wire — purple white goo - the molecules of life.

What is happening:

DNA is found in every cell of every living thing, but it is difficult to get it out and disentangle the DNA from the protein inside the cells.

The composition of Kiwi fruit allows the DNA to be extracted without a great deal of effort, but not all things do. By chopping the Kiwi fruit and letting it soak in the detergent and salt the first part of the problem is solved. The detergent strips away the cell membranes that cover the inside of the cell and lets the internal goo escape. The kiwi fruit needs to be chopped fine enough to get the cells broken open, but this should not be overdone or the DNA will be smashed.

The second part of the problem, getting rid of the protein that has stuck to the DNA is all done by the Kiwi fruit. The Kiwi fruit already contains a lot of a special enzyme called a proteinase. Enzymes are like small molecular machines that do many things — the enzymes in washing powder digest fat for example. The proteinase enzyme attacks the proteins clinging to the DNA and breaks them up thereby releasing the DNA. Rosalind Franklin tried oranges, but oranges do not contain enzymes and therefore she failed to make DNA from them. She and Raymond Gosling finished up having a food fight with the residue of their efforts.

The green layer that is produced in the glass is full of DNA as well as lots of broken up proteins and other things. When the cold meths is poured onto the green layer, the DNA dissolved in the water layer at the bottom of the glass is turned into a solid as the DNA cannot remain in the solution. Little bubbles may form between the two layers and drag the strands of DNA up into the meths — the bubbles may be caused by the temperature difference between the layers, making the air dissolved in the green layer come out of the solution. © BA GMH

We hope that this information has been useful to you.