Extraction of DNA from onions

Essay by marinichole528 March 2012

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Extraction of DNA from Onions


The purpose of the experiment was to experience firsthand the isolation of DNA form a plant tissue without destroying its structure and sequence. A white onion was used for the experiment. After several processes, DNA isolate was the visible result. Different chemical tests were performed on the DNA isolate, namely: Dische Test, Murexide Test, Wheeler-Johnson test and Test for Phosphate. Visible results were then noted.


DNA (deoxyribonucleic acid) was discovered in the late 1800s, but its role as the material of heredity was not elucidated for fifty years after that. It occupies a central and critical role in the cell as the genetic information in which all the information required to duplicate and maintain the organism.

Today, Scientists can analyze DNA from minute samples of blood, hair roots and saliva, but before they can analyze DNA, scientists must be able to extract it.

The process of DNA extraction is the first step for many laboratory procedures. Scientists must be able to isolate the DNA from the other unwanted substances of the cell gently enough so that the DNA is not broken up.

For this experiment, an onion was used because of its low starch content, which allows the DNA to be more clearly seen. The salt shields the negative phosphate ends of DNA, which allows these ends to come closer so that the DNA can precipitate out of a cold alcohol solution. The homogenizing solution causes the cell membrane to break down by dissolving the lipids and proteins of the cell, which disturbs the bonds that hold the cell membrane together. The homogenizing solution then forms complexes with the lipids and proteins causing them to precipitate out of the solution.

After the isolation of the DNA from the solution, different chemical...