To isolate DNA from a plant tissue

Video

Step 1

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

Step 2

Add chopped onion to a beaker. Pour in the salty washing-up liquid solution and stir.

• 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

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

Step 4

Cool the mixture by standing the beaker in an ice bath for 5 minutes.

• Stops DNA from breaking down

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

Step 6

Filter the blended mixture through coffee filter paper.

• Filtrate = DNA + proteins• Coffee filter paper has

larger pores than lab filter paper

Step 7

Add 2-3 drops of protease enzyme to 10 ml of the onion extract.

Protease breaks down protein surrounding DNA

Step 8

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.

Step 9

DNA forms at the interface of the ethanol and extract.

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

Mock 2010

Answers

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