Name ______Date ______Hr ______

DNA EXTRACTION Lab

You've just learned about DNA, but have you ever seen it? With the DNA extraction experiment, you'll observe the DNA of fruit in a matter of minutes. It sounds impossible, but thanks to some basic science, it's actually very possible… and simple. You don't have to be a geneticist. You don't need a microscope. It's easy, fun, and all you need are some household materials.

Materials:

Name ______Date ______Hr ______

Homogenization medium

Fruit

~10ml ICE COLD Ethanol alcohol

Test tube

Test tube rack

1 piece of filter paper

2 -50mL beakers

1 wooden splint

Rubber band

Name ______Date ______Hr ______

Procedure:

Observing DNA from plants, animals, blood, tissue, or saliva, requires the same basic principles. First, the cell membranes must be broken to release the DNA. We will do this by adding a “homogenization medium” made of detergent (soap) and salt. Then we will break the sample up into many small pieces (in a blender or mashing in a bag) to allow the detergent to reach all of the cells. This is really important in plants since both the cell wall and the cell membrane must be broken to release the DNA.

1. Place a small piece of fruit into the sealable bag. Mash well for 2 minutes.

2. Squish fruit into a corner of your bag and place 15 mL of homogenization medium onto the fruit.

3. Seal the bag and mush together for 1 minute.

4. Filtration Set-Up:

Place a coffee filter over a small beaker. Make sure the filter creates a pocket deep enough to hold the mixture, and covers over the top sides of the cups. Secure with a rubber band.

5. Open up the bag and slowly pour the mixture into the filter. Do not overflow. Be Patient!

6. When most of the mixture has filtered through, throw away the filter, but save the rubber band.

At this point, the DNA should all be in the liquid. The extra pieces of tissue should be filtered out. In order to see the DNA we will add alcohol, very slowly. DNA does not dissolve in alcohol so it will not mix with it. DNA is also less dense than alcohol so it will form a layer on top of the alcohol.

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7.  Pour your filtered solution into a clean test tube.

8.  SLOWLY Add ice-cold ethanol alcohol to the test tube to create an alcohol layer approximately 1-2cm thick on top of the filtrate. Gently tip the test tube and slowly pour the alcohol down the inside of the test tube.

9.  Place your test tube in the rack and observe for several minutes without shaking or mixing. Small bubbles will appear, and cloudiness will be seen between the layer of filtrate and the alcohol.

10.  After 1 minute, insert the wooded splint into the top layer and touch the bubbled area. Twist and turn the splint, and gently pass it back and forth between the DNA and the filtrate. You may want to drag the material up the side. Do this slowly so as not to cause too much mixing of the layers. The DNA should gather on your splint. It will look white and stringy.

11.  Show your teacher your DNA and get initials. Teacher initials for DNA extraction ______

12.  Clean up your lab station and get signed out. Teacher initials for clean lab station ______

How does it work?

Whoa! Did you know that DNA is in the food you eat? The long thick fibers you pull out of the extraction solution are strands of strawberry or banana DNA. DNA is in every cell of all plants and animals and holds their genetic information.

While other fruits are soft and just as easy to mash, strawberries and bananas are the perfect choice for a DNA extraction lab for two reasons: they produce more DNA than any other fruits, and they are octoploid, meaning that they have eight copies of each type of DNA. The two things make strawberry and banana DNA easy to remove and see. Human cells are generally diploid, meanings they have only two copies of each type of DNA.

To extract the DNA, each component of the extraction solution plays a part. The soap helps to dissolve the cell membranes. The salt is added to break up protein chains that hold the DNA strands together. Finally, DNA is not soluble (dissolvable) in alcohol, and even less so when the alcohol is ice cold.

Analysis:

1.  Describe what the DNA looked like.

2.  What was the purpose of the homogenization medium (the dish soap and salt mixture solution)?

a.  Could you extract DNA without this step?

3.  What fruit did you use? ______Why did we mush the fruit?

4.  What are two reasons the DNA made a layer on top of the alcohol?

5.  How did you know if you successfully collected DNA?

6.  From what types of organisms can DNA evidence be collected?