Download DNA Extraction from Bacteria

DNA Extraction from Bacteria
DNA carries in its molecular structure the genetic information for cell development and
behavior. Consequently, all living cells contain DNA. DNA can be isolated from cells of
any plant, animal, or microorganism. In this laboratory procedure, you will isolate DNA
from Escherichia coli.
Supplies required – (Students should work in pairs or groups)
•
1 capped test tube containing Escherichia coli
•
detergent solution (diluted clear shampoo or 10% SDS)
•
1 capped test tube of chilled 95% ethanol. You can find this in the freezer of the
refrigerator at the back of the lab. For best results, this ethanol should be as cold as
possible.
•
meat tenderizer
•
1 flat toothpick
•
1 Pasteur pipette or medicine dropper with a rubber bulb attached
Step 1. Add about 1 inch of detergent solution to the tube containing the
bacteria. Cap the tube; invert slowly several times to gently mix the
solution without foaming. Place the tube in a hot water bath at 55-60°C
for 10 minutes.
Detergent and heating dissolve the fats in the walls of the bacteria causing
the cell to burst, which frees the genetic material.
Step 2. Remove the test tube from the hot water bath. Add two flat
toothpicks full of meat tenderizer to the tube, cap the tube, mix gently but
thoroughly, and return the tube to the 55-60°C water bath for 20 minutes.
Meat tenderizer contains papain, an enzyme that breaks down any proteins
that may be attached to the DNA.
Step 3. Remove the tube from the hot water bath. Add cold alcohol to the
test tube (about 2/3 full) to create an alcohol layer on top of the bacterial
solution. Do this by slowly pouring the alcohol down the inside of the test
tube with a Pasteur pipette or medicine dropper. DO NOT MIX!
DNA is soluble in water but not alcohol. When alcohol is added to the
mixture, all the components of the mixture, except for the DNA, stay in
solution while the DNA precipitates out into the alcohol layer.
Step 4. Let the solution sit for 2-3 minutes without disturbing it. It is
important not to shake the test tube. Watch the white DNA precipitate out
into the alcohol layer.
DNA has the appearance of white mucus.