Lab 5 Activities Continued

DNA Extraction

Before You Begin

Answer the following questions with your lab group:

1. What are fruits?
   • Where do they come from?
   • What are they made of?
2. Use phylogeny to classify plants (DKPCOFGS).
3. Where is DNA located within the fruits? Where is it located in you?
4. Why would you want to extract DNA from an organism?
5. What class of molecule is DNA?

Materials

Each lab group will need the following materials:

• sample of fruit (banana, strawberry, or grapes)
• salt solution
• liquid detergent (soap)
• cold ethanol
• 1 Ziplock bag
• 1 coffee filter
• 1 rubber band
• 1 beaker
• 2 test tubes
• test tube rack
• stirrer or glass rod

Method

1. Mash about 10 g or 3 cm of over-ripe banana OR 3 grapes OR 1 strawberry in zip-top bag.
   • Over-ripe banana is best since the cell walls are already decomposing.
   • Physical mashing continues to break up the cell walls.

2. Add 7 ml of salt solution.
   • The salt solution helps the DNA to aggregate (clump together).

3. Add 7 ml of liquid detergent and mix.
   • The detergent dissolves the lipids in the cell and nuclear membranes.
   • This releases the DNA into the salt solution.

4. Place a coffee filter over a cup or beaker and fasten with an elastic band. Pour the mash into the filter and wait for the liquid to drip through the filter.

5. Pour about 5 ml of filtrate into a test tube.

6. Slowly pour an EQUAL volume of cold ethanol down the side of tube to form a layer on top of the fruit fluid.
   • Carefully run the alcohol down the side to form a separate layer on top of the fruit solution.
   • Do not mix the alcohol and the fruit solution.
   • Ice-cold 100% ethanol works best.

7. Spool the DNA: use a plastic loop or glass rod to gently swirl at the interface of the two solutions.
   • The interface is where the two solutions meet.
   • DNA is not soluble in alcohol.
   • Bubbles may form around a wooly substance (this is the DNA).

8. Transfer the DNA to an empty test tube.

Method Images

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