Prelab Questions
- What are fruits?
- Where do they come from?
- What are they made of?
- Use phylogeny to classify plants (DKPCOFGS)
- Where is DNA located within the fruits? Where is it located in you?
- Why would you want to extract DNA from an organism?
- What class of molecule is DNA?
Methods: Extraction of DNA from fruit
- Mash about 10g or 3cm 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
- Add 7ml of salt solution
- The salt solution helps the DNA to aggregate (clump together).
- Add 2 ml of liquid detergent and mix
- dissolves the lipids in the cell and nuclear membranes
- releases DNA into the salt solution
- Place a coffee filter over a cup or beaker and fasten with an elastic band
- Pour mash through filter into a beaker
- removes cell debris
- Pour about 5 ml of filtrate into a test tube
- 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 banana solution.
- Ice-cold 100% ethanol works best
- 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)
Dische Diphenylamine Test For DNA
- Obtain 3 test tubes and number them 1-3.
- Suspend the spooled DNA in 3 ml of distilled water. MIX.
- Add to tubes:
- 2 ml of DNA solution
- 1 ml of DNA solution with 1 ml H2O
- 2 ml of H2O
- Add 2 ml of the Dische’s diphenylamine reagent to each tube and mix thoroughly.
- Place in a boiling water bath for 20 minutes.
- Evaluate your results. A clear tube indicates no nucleic acids. A blue color indicates the presence of DNA. A greenish color indicates the presence of RNA.