WISE 2007-2008

Strawberry DNA

DNA (deoxyribonucleic acid) is the building block of life – the master molecule that encodes all the information needed to create and direct cellular structures and processes. Without DNA, life as we know it would not exist! Today’s scientists can analyze DNA obtained from samples of blood, saliva, or hair roots. In fact, thanks to DNA technology, scientists have the ability to clone a wooly mammoth, an animal lost in the ice age, from samples preserved in the permafrost.

To most students of biology, DNA remains an abstraction. You can memorize the names and structures of the nitrogenous bases and know all about the history of DNA’s discovery, but until you actually handle DNA, it remains a strange and mysterious substance.

The purpose of this laboratory is to give you firsthand experience with DNA by isolating it from plant tissue. You will start with strawberries and end with a relatively pure preparation of DNA, containing literally billions of genes. Once isolated, it will be actually possible for you to hold in your hands the key to an organism’s development and structure!

Directions: PUT ON GOGGLES!

1. Make sure the bag containing the strawberry is sealed. Mash the strawberry in the bag with your hands until it becomes a liquid.

2. On you pink tray, you will be find a small cup holding 5 mL of SDS, a salted, mild detergent. Open your Ziploc bag and pour in the SDS. Seal the bag and continue mashing so that you mix the SDS in with the liquid strawberry.

3. After mixing, pour the strawberry mixture into the test tube on the tray.

4. Take the test tube to the front of the room to a volunteer who will add 1 mL of ice cold ethanol down the side of the tube.

DO NOT MIX THE ETHANOL with the strawberry mixture.

5. Return to your table and watch the clear layer of ethanol above the strawberry layer.

What do you see? You should see bubbles and the formation of a white precipitate in the layer. This is actually DNA strands!

6.Use the wooden splint to twist the DNA out of the test tube. Touch it with your fingers. It should be sticky!

7. You can add another 1 mL of cold ethanol to repeat the DNA extraction!