Experiment on Chromatin Isolation

             DNA is the blueprint for all living things. DNA is made of a material called chromatin. The purpose of this experiment was to attempt to isolate, or separate, chromatin from onion cells. My lab partner was Dave Sugg. .

             Hypothesis: We should be able to isolate DNA from onion cells.

             Procedure: To begin, weigh out about 15 grams of onion cubes and place it in a 400 ml beaker. Add about 60 ml of homogenizing medium to the onion cubes. Place it in a warm water bath for 8 minutes. Don't let it tip over!!! This softens onion tissue and allows homogenizing medium to penetrate the onion. The enzymes also get denatured. Quickly cool the solution to 15-20 degrees Celsius in an ice bath. Don't let it tip over!! Put the cooled solution in a blender. Blend for 45 seconds at high speed. Pour the result into a 500 ml beaker. Put this into an ice bath for 8 minutes. Set up a filter (cheesecloth - 2 layers) in a funnel during the 8 minute wait. Pour the white solution through the filter into the other 500 ml beaker (leave the foam behind!). Take 25 ml of filtrate and pour it into a clean 250 ml Erlenmeyer flask. Put the flask in an ice bath until it cools to 10 - 15 degrees Celsius. Slowly add 50 ml of ice cold ethanol down the side of the flask until a white, stringy chromatin precipitate occurs (the stuff will look stringy and cloudy). Wind the stringy DNA on a glass rod by turning the rod in one direction only.

             Data: Before we poured the ice cold ethanol down the side of the flask in the final step, there was a film at the top of the solution. We poured in all 80 ml of ethanol. There were 3 clear layers; a clear ethanol layer at the top, a DNA interface, clear with whitish strands, and quite visible unlike the protein, and a yellow homogenate at the bottom.

             This experiment taught us the process of isolating DNA from onion cells. We learned a great deal from the completion of these extractions. We had the thrill of observing DNA, the genetic messenger of life, in its visible form.

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