Isolating DNA

What you need

• about a third of a banana
• a spoon
• a kitchen chopping board
• a cup
• a beaker
• a funnel
• a paper coffee filter (V60)
• salt (2 pinches)
• shampoo
• distilled water
• alcohol (chilled, from the fridge)
• a Petri dish or clear glass saucer
• a sheet of black paper or a dark surface

Procedure

1. Mix the shampoo and salt in the cup.

2. Pour in the distilled water and carefully mix again so that the liquid does not foam.

3. On the chopping board, cut the banana into pieces with the side of the spoon.

4. Place the sliced banana in the cup with the prepared mixture.

5. Use the back of the spoon to mash the banana finely against the sides of the cup.

6. Place the funnel on the beaker or a jar and put the paper coffee filter in it. Pour in the mixture and let it drip through the filter. This process can take several minutes.

7. Place the Petri dish or clear glass saucer on a dark surface (for light). Pour the chilled alcohol into the dish or saucer and add a drop of the filtered solution with the banana.

8. Take a look at it through a magnifying glass. You'll see precipitated white DNA in the alcohol!

Explanation

DNA is found in the nucleus of the cell. In a plant cell, it is protected by two types of barriers – a solid cell wall and lipid membranes. Squeezing the fruit pulp breaks the outer cell wall. The inner membranes are broken up by the shampoo. Along with the DNA, other substances such as DNA-cleaving enzymes (DNases) are released into the solution. DNase activity has to be prevented – it would decompose "our" DNA. DNases need magnesium ion to function properly. If we isolate the DNA using a shampoo with added EDTA (ethylenediaminetetraacetic acid), the magnesium ions bind to it, putting the DNases out of action. Filtering solution then removes all the insoluble parts of the cell from it. Pouring the solution into cold ethanol (alcohol) causes the DNA to precipitate.

See more experiments with Mendel here.