Extraction of DNA from onions

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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
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The heat softens the membrane as a whole. This entire step, homogenation, is used to free the DNA from its protective barriers.

Then crude papain was added, because Deproteinization which involves adding a protease enzyme Papain will denature the proteins clinging to the DNA making the molecule flexible and easy to spool. Then the solution was then heated again to 60 degrees for 10 minutes with occasional stirring.

Then it was placed in an ice bath, this is because by cooling the solution, it will help prevent denaturation, which might destroy the DNA if it was exposed to prolonged heating. Swirling was done in order not to "shock" the DNA from the sudden change in temperature.

After putting it in an ice bath, the solution was then placed in a blender and was blended for 45 seconds, after. This was done because the procedure also frees the DNA from another protective barrier, the thick cell wall that all plant cells have. The blending should cause many of the cell walls, containing cellulose, to break, and therefore leave the DNA in the cytoplasm, and no protective thick cellulose wall blocking the cytoplasm from its external environment. We did not need to do this to the bacteria because it does not have a cell wall.

The blended solution was then filtered through 4 layers of cheesecloth leaving the foam untouched. This is because it

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