Download 1.2.2 DNA Extraction Notes

DNA Extraction and Isolation
DNA in the Cell
• DNA is found in cells, particularly in the
nucleus or most animal and plant cells.
Why Extract the DNA?
1. Genetic testing
2. Body identification
3. Forensic evidence analysis
How do we get the DNA from cells?
• Extracting and Isolating DNA from cells take
place in essentially 3 steps:
• Additional step for plant cells: grind plant
matter to break cell walls
1. Lysing (breaking) the cells to release DNA
2. Separating cellular and protein debris from
DNA
3. Precipitating and isolating the DNA
Grinding Plant Matter
• Plant cells contain cell walls which are
tough and surround the cell membrane
• Plant material should be physically ground
so that the cells walls are broken down
Step 1: Lysing Cellular and Nuclear
Membranes
• Both cell (plasma) and nuclear
membranes are made of lipid (fat)-based
molecules called phospholipids in 2 layers
called a bilayer
• Nuclear membrane is a double bilayer
Step 1: Lysing Cellular and Nuclear
Membranes
• A lysis buffer which contains a mild
detergents helps to break apart both the
cell and nuclear membrane to release the
DNA contents
Step 2: Separating Debris from
DNA
• DNA is wrapped in a tightly coiled form
called a chromosome
• DNA wrap around proteins called histones
so that the coiling is more compact
Step 2: Separating Debris from
DNA
• Adding salts (and proteases, enzymes that
break down proteins) helps to remove the
histones and other protein debris by
neutralizing the DNA’s charge
Step 3: Precipitating the DNA
• The DNA is still dissolved in water at this
point.
• Adding cold alcohol (either ethanol or
isopropanol) will make DNA less soluble in
water and it will precipitate out in the
alcohol layer (top layer)