DNA Mechanisms of Genetics

DNA Extraction Lab

Deoxyribose nucleic acid (DNA) is found in all organisms. Strawberries are an excellent source for extracting DNA. They are soft and can be pulverized easily. In addition, strawberries have very large genomes. They have eight copies of each chromosome, in other words, which makes them octoploid. For comparison, humans are diploid, having only two copies of each chromosome.

In this lab, you need to extract DNA from the cell of an organism. An extraction buffer containing salt and dish soap will be used to extract the DNA from the cells. The salt shields the negative phosphate groups of the DNA so that the DNA will become less soluble and can precipitate out of the lysate as well as breaks up the proteins that hold the nucleic acids together, while the dish soap helps to dissolve the lipid layer of the cell membranes. In certain versions of this lab, meat tenderizer is also used.  Meat tenderizer contains enzymes that will destroy the proteins, called histones.  Histones stick to and bind up the DNA and protein enzymes called DNases.  DNases are enzymes that destroy DNA.  The 95% ethanol will cause the DNA to become an insoluble precipitate. In Part II, you will discover that even though the size and location of the DNA may vary among species, the components of DNA are the same. 

Procedure:

1.   Place one piece of strawberry in a plastic baggie.
2.   Smash the strawberry with your fingers for 2-3 minutes.
Make sure that you do not break the bag!
3.   Add 10 mL of extraction buffer to the bag.

Filter 

4.   Mix the extraction buffer and strawberry together using your fingers. Knead the mixture for one minute.
5.   Make the filtration apparatus as shown in the diagram.
6.   Pour the strawberry solution into the filtration apparatus.
The solution will take a while to drip and filter out the liquid from the solid pieces.
7.   Remove the filtration apparatus from the test tube.
8.   Slowly drizzle the alcohol into the test tube. Tilt the test tube so that the alcohol runs down the side of the glass.
9.   Hold the test tube at eye level. Can you see a white cloudy mixture where the alcohol and strawberry solution meet?
10. Dip the wire hook into the test tube where the two liquids meet.
11. Gently use the wire hook to gather the DNA.

Complete Part I in your Student Journal.