2.3.4 DNA Purification

Question 1

How can we isolate DNA from cells?

Answer 1

• Precipitation
• Lysis of cells disrupting nuclear membranes to release DNA
• Enzymes denature histones
• Ethanol or appropriate solvent used to precipitate DNA

Question 2

Method to extract DNA from onions

Answer 2

1. Cut onion into small pieces
2. Washing up liquid + water into beaker
3. Add onion pieces to beaker
4. Water bath at 60 degrees for 5 minutes
   (Detergent and heat disrupt phospholipid bilayer releasing DNA)
   (Heat denatures enzymes from cell that would digest DNA)
5. Cool mixture in ice bath for 5 mins, stir
   (low temps prevent DNA from breaking down)
6. Blend mixture for 5 seconds
   (breaks cell walls and membranes releasing more DNA)
   (short blend so DNA strands aren’t broken apart)
7. Filter mixture into beaker using filter paper
   (removes membrane fragments and cell debris)
   (filtrate now contains DNA and its proteins)
8. Pour 10cm^3 of filtrate into test tube, add 2-3 drops of protease, mix
9. Add ice cold ethanol and wait 2-3 mins
   (nucleic acids are insoluble in ice cold ethanol so DNA forms precipitate (white layer at top of test tube))
10. Extract DNA and use for analysis