DNA EXTRACTION LAB
Objective
The purpose of this lab is to extract DNA from the nuclei of an onion, cup of strawberries or a banana.
Introduction
In every eukaryotic cell there are long strings of DNA. The DNA encodes for every protein needed by the organism. The DNA can be millions and millions of bases long. When the DNA is in the nucleus, it is tightly coiled around a set of proteins called the histones. When DNA is released from the nucleus by detergent, it can become long and stringy. In this lab we are going to be extracting the DNA from the nuclei of onions and wrapping the DNA around a glass rod.
Materials
Straw or Coffee Stirrer
2-plastic water bottles (single serving disposable)
Ice
Rubbing Alcohol
Liquid soap (laundry detergent) DawnR works best
Coffee filter
Water- distilled
Onion, Cup of Strawberries, or Banana
Table salt
Procedure
1. First place a bottle of rubbing alcohol on ice to chill.
2. Then make the following detergent/salt solution:
Mix together (1/8 cup) 20 mL of liquid soap, (2-tsp) 20 grams of salt, and (1 1/8 cup) 180 mL of distilled water. When you are finished making the solution, put it on ice to chill for at least 10 minutes.
3. Cut an onion in half and chop it up either in the blender, or with a knife. If using strawberries chop them up to small pieces. If using the banana smash it up in a cup.
4. Add (half) 100 mL of the detergent/salt solution to the chopped onion, strawberries, or banana. Continue crushing the onion, the onion needs to be pulverized.
5. Let the slurry sit for 5 minutes on ice.
6. Cut the top 1/3 from the water bottle and flip it over onto the lower cut portion. Use the top as a funnel and the lower portion to catch the solution as it filters through.
7. Place a coffee filter in the top funnel. Pour the slurry through and capture the filtered solution below.
8. Once all of the slurry is in the beaker slightly tilt the beaker and slowly pour down the side of the beaker an equal volume of ice cold rubbing alcohol. This will form two distinct layers. A white stringy material will form at the interface of the two layers.
* Do not mix the alcohol and the slurry.
8. Carefully insert a glass stir rod in the center of the beaker, being cautious not to touch the sides.
9. Now, twist the stir rod in a clockwise direction (like twirling spaghetti) and you should see a white stringy material collecting onto the rod.
This white stringy material is DNA. Keep twisting until you acquire the maximum amount of DNA.
* If you do not collect any DNA on the stir rod then use a piece of sandpaper to rough up the end of the stir rod and try again.
Questions
What did you observe?
Were you able to isolate DNA?
What did it look like?
