• Deoxyribonucleic acid (DNA) extraction is the process by 
     which DNA is separated from proteins, membranes, and 
     other cellular material contained in the cell from which it 
     is recovered.
     • The DNA extraction process requires careful handling of 
     biological material to prevent sample contamination and 
     crossover. Tubes should be carefully labelled, especially 
     when transfers are required.
      • The simplest cells, such as bacteria cells, are prokaryotes. 
       These prokaryotes comprise a lipid bilayer outer 
       membrane  and a cytoplasm containing a 
       circular chromosome, proteins, inorganic salts and metal 
       ions, sugar molecules, and other elements of cell 
       machinery.
      • Humans, animals, and plants are composed of eukaryotic 
       cells; these cells also have a lipid bilayer outer membrane 
       and cytoplasm containing proteins, sugars, lipids, 
       and inorganic ions of various types and function.
      • However, eukaryotic cells also contain other membrane-
       enclosed compartments called organelles. The nucleus of 
       a cell is an organelle that houses 46 chromosomes, and 
       the mitochondria each house a circular DNA chromosome, 
       all of which direct the production of proteins.
       Basic Steps in DNA Extraction
         Lysis      Precipita   Purificati
                      tion          on
                 STEP 1 - Lysis
      • In this step, the cell and the nucleus are broken open to release the 
       DNA inside and there are two processes involved in this:
      •  First, mechanical disruption breaks open the cells. This can be done 
       with a tissue homogenizer (like a small blender), with a mortar and 
       pestle, vortexing or by cutting the tissue into small pieces (depending 
       on the type of sample). Mechanical disruption is particularly 
       important when using plant cells because they have a tough cell wall.
      • Secondly, lysis is completed using detergents and enzymes such as 
       Proteinase K to free the DNA and dissolve cellular proteins. The 
       detergent breaks down the lipids in the cell membrane and nuclei, 
       while the proteinase K dissolves DNA associated proteins and cellular 
       proteins.
           STEP 2 - Precipitation
      • After the completion of the lysis step, the DNA has been freed 
      from the nucleus, but it is now mixed with mashed up cell 
      parts. Precipitation separates DNA from this cellular debris. 
      First, concentrated salt such as Na+ ions (sodium) is added, 
      which neutralizes the negative charges on the DNA molecules, 
      thus makes them more stable and less water soluble. Next, ice-
      cold alcohol (such as ethanol or isopropanol) is added and 
      causes the DNA to precipitate out of the aqueous solution 
      because DNA is insoluble in the presence of salt and alcohol.
      • By gently stirring the alcohol layer with a sterile pipette, a 
      precipitate becomes visible and can be spooled out. If there is 
      lots of DNA, you may see a stringy, white precipitate.