Name: __________________________________________________
Date_________________
LAB 5 - DNA EXTRACTION
Materials:
knife
resealable bag
dishwashing liquid
1 cup of fruit
clean piece of cloth or strainer for filtering
mortar and pestle
table salt
70% rubbing alcohol (chilled)
2 250mL beaker
stirring rod
funnel
test tube
test tube rack
How to do the extraction:
Before you begin, make sure you have chilled your alcohol in the freezer for at least 3 hours. Room temperature
alcohol will not work nearly as well as cold alcohol. Place about 50 mL of alcohol in the freezer to chill it and take it
out only when you’re going to need it. (The alcohol will not actually freeze.)
1. The first thing you will need is a sample. Since DNA is found in all living things, an inexpensive fruit can be used. You
can use banana, apple, papaya, tomato or mango for a better chance to see the DNA clump.
2. The DNA is contained inside the nucleus of the cell. To release it, we need to break down the plant matter, then
break open the cell and finally break in to the nucleus of the cell.
Your first step is to break apart the plant matter. That means crushing the fruit using mortar and pestle or a blender
(if available). Add about 1 cup of crushed fruit (including the juice) to the resealable bag, remove the air, and seal.
3. Now we need something to break open the cell walls. It turns out that cell walls are made up of things called lipids,
or fats. If you had greasy or fat coated dishes in the kitchen, you would use a detergent to clean it up. We are going to
do the same thing to break open those cell and nuclei walls to release the DNA.
4. Fill a clear glass with 1/2 cup of water. Slowly add in 3 tablespoons of dish soap and 1 tablespoon of table salt.
Gently mix this solution without making bubbles until most of the salt
dissolves. The salt will later help the DNA stick together.
5. Add this solution to your resealable bag of squished up fruit. Add enough
so that you have a nice mixture that you cannot see through. Flatten out
your baggie to remove most of the air and then seal it up. Gently squish the
liquid around. Let this mixture sit for at least 30 minutes to give the
detergent time to release a lot of DNA.
6. Filtering out the plant matter is the next step. Place a clean piece of cloth
or strainer on top of a cup and carefully pour your fruit mixture into the
filter. You can gently squeeze the filter to get more liquid out. This is the
solution that contains the DNA. Since the DNA is soluble in water we need
something else to sort of pull it out of the solution. For this we will use
rubbing alcohol. You will want to use at least 70% alcohol for the extraction.
The higher the concentration of alcohol the better it will work to make the
DNA come out of the water solution.
7. Transfer the DNA solution in a test tube. Very carefully pour the chilled alcohol down the side of the glass. You are
trying to create a layer of alcohol that floats on the top of the DNA solution. The DNA will come out of solution at the
boundary layer between the water and alcohol. You should see some almost cotton like strands beginning to appear
in the glass. That is the DNA clump (not the double helix molecule because it is too small).
8. Let the solution sit for a few minutes and you should see more DNA come out of the solution. If you want to save
your DNA you can store it in a small container filled with the rubbing alcohol.
Attach the extracted DNA setup below.
Questions:
1. Why do we need to crush the fruit?
2. Why do we use liquid detergent?
3. What does the salt do?
4. What does the cold alcohol do?
5. Why can’t we use room temperature alcohol?