Download Biology DNA Extraction

Biology
DNA Extraction
Courtesy: Carl Bird
Pre-lab Activity: DO NOW
Where is DNA found?
Today we will isolate DNA from plant cells.
What structures separate DNA from the outside world? What are these structures made of?
What are enzymes? What do they do?
When you observe DNA today, what do you think it will look like?
First, you need to find something that contains DNA.
Since DNA is the blueprint for life, everything living
contains DNA. For this experiment, we like to use
Strawberries.
Ripe strawberries are an excellent source for extracting
DNA because they are easy to pulverize and contain
enzymes called pectinases and cellulases that help to
break down cell walls. Strawberries have eight copies of
each chromosome (they are octoploid), so there is a lot of
DNA to isolate. And most important, they smell nice!
Other good sources include chicken liver, calf thymus, meats eggs, peas and broccoli.
Super Strawberry Smash Melee!
-Obtain 2 strawberries and a plastic Ziploc bag.
-Remove the green sepals from the strawberries.
-Place strawberries into a Ziploc bag and seal shut.
-Squish for a few minutes to completely squash the fruit.
Soapy Strawberries
Add 10 ml of liquid detergent to
the bag and mix for two minutes.
Try not to make a lot of soap
bubbles.
Place coffee filter paper above a
collection beaker.
Pour your strawberry soup through
coffee filter paper above a
collection beaker.
Allow the liquid strawberries to filter through the coffee paper. The filter paper will remove the fluid
(which contains DNA) to drain into the beaker below. The proteins and other cellular debris stay
behind. Allow filtrate to sit for five minutes.
Pour the mixture into test tubes or other small glass containers, each about 1/3 full.
Enzyme Power
Add a pinch of meat tenderizer enzymes to each test
tube and stir gently. Be careful! If you stir too hard,
you’ll break up the DNA, making it harder to see.
If meat tenderizer isn’t available, you can also try using
pineapple juice or contact lens cleaning solution.
Alcohol Separation
Tilt your test tube and slowly pour rubbing
alcohol (70-95% isopropyl or ethyl alcohol)
into the tube down the side so that it forms a
layer on top of the strawberry mixture. Pour
until you have about the same amount of
alcohol in the tube as strawberry mixture.
Watch for about a minute. What do you see?
You should see a white fluffy cloud at the
interface between the two liquids. That’s DNA!
Gently spin a stirring rod or pencil in the tube
where into the tube where the strawberry
mixture and the alcohol layers come into
contact with each other.
Pull out the DNA! The fibers are millions of
DNA strands.
Rinse your funnel. Put the Ziploc TM bag and
paper towel in the garbage.
Using this same basic protocol, human DNA
could also be extracted. The protocol however
would have to be scaled down. This is because
you would likely start the procedure with
micrograms rather than grams of human cells. The DNA extracted in this protocol would not be
enough to see with the naked eye. If you wanted to see it, you would need a centrifuge to spin
down the small amount of DNA present in the sample.
QUESTIONS
1. Explain what happened in the final step when you added isopropyl alcohol to your
filtered DNA extract?
2. What did the DNA look like? Relate what you know about the chemical structure of
DNA to what you observed today.
3. A person cannot see a single cotton thread 100 feet away, but if you wound
thousands of threads together into a rope, it would be visible much further away.
Is this statement analogous to our DNA Extraction? Explain.
4. Why is it important for scientists to be able to remove DNA from an organism? List
two reasons.
5. What was the purpose of the meat tenderizer? What type of organic
macromolecule would be present in meat tenderizer?
6. In the space below, please write some research questions based on what you
observed
(would you like to try this experiment on something else? Would you like to see
how the procedure worked if modified?)