1. To isolate DNA from a plant tissue
Video

2. Step 1
Add 10 ml washing-up liquid and 3 g salt to a graduated cylinder. Make up to 100 ml and stir.

3. Step 2
Chopped onion = increase surface area and breaks cell walls
Washing up liquid breaks down cell membranes, which releases DNA from cells.
Salt causes DNA to clump together
Add chopped onion to a beaker. Pour in the salty washing-up liquid solution and stir.

4. Stand the beaker in a water bath at 60°C for 15 minutes.
Step 3
Stand the beaker in a water bath at 60°C for 15 minutes.
Heat denatures enzymes that would break down DNA.
After 15 minutes, DNA itself would be broken down

5. Cool the mixture by standing the beaker in an ice bath for 5 minutes.
Step 4
Cool the mixture by standing the beaker in an ice bath for 5 minutes.
Stops DNA from breaking down

6. Blend the mixture for no more than 3 seconds.
Step 5
Blend the mixture for no more than 3 seconds.
Breaks down cell walls and releases DNA.
Any longer than 3 seconds and DNA strands would break down

7. Filter the blended mixture through coffee filter paper.
Step 6
Filter the blended mixture through coffee filter paper.
Filtrate = DNA + proteins
Coffee filter paper has larger pores than lab filter paper

8. Add 2-3 drops of protease enzyme to 10 ml of the onion extract.
Step 7
Add 2-3 drops of protease enzyme to 10 ml of the onion extract.
Protease breaks down protein surrounding DNA

9. Step 8 DNA is insoluble in ice cold ethanol.
Very carefully, pour 10 ml of ice cold ethanol onto the surface of the onion extract.
DNA is insoluble in ice cold ethanol.
It percipitates at the top.

10. DNA forms at the interface of the ethanol and extract.
Step 9
DNA forms at the interface of the ethanol and extract.

11. Draw the DNA out of the solution by wrapping it around a glass rod.
Step 10
Draw the DNA out of the solution by wrapping it around a glass rod.
DNA forms a clear cobweb-like mesh that looks like stringy mucus

12. Mock 2010

13. Answers

14. END