DNA Isolation from Onion

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Scientists are involved with research in finding out as much as possible about the DNA in plants and animals. Although DNA was discovered in the 1950͛s, there still remains a lot to be known about it, especially how it regulates the workings of the body and how it is used to determine the corporeal traits that we all have. We should always remember that DNA is just a chemical named á

   á. Because it is a chemical, we can do reactions with it just like we can work with any other chemical. In this lab, we will use the chemical properties of DNA to extract it from the cells of onions.YY


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Y    Y YRhe purpose of this laboratory is to give you firsthand experience with DNA by isolating it from plant tissue. You will start with whole onions and end with a relatively pure preparation of DNA, containing literally millions of genes. Once isolated, the DNA can be stored in alcohol or dried out. It will actually be possible for you to hold in your hands the key to an organism's development and structure.YY Y

  


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    1)Y Dice an onion with a knife. Half an onion should be plenty for this lab. Use a mortar and pestle to mash the pieces of onion into a pulpy sludge. 2)Y Adding distilled water, homogenate in a blender for about 40seconds. 3)Y Rransfer the blended onion into a 250mL, using a funnel. 4)Y Add 1mL of 10% SDS and stir. 5)Y Heat the solution. 6)Y Let the mixture cool for 5 minutes. 7)Y Rransfer to a test tube using a 50mL pipette, and then add ethanol (ice cold) slowly pipetting down the side of the tube.



 

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  A clear layer of ethanol should form on top of the onion filtrate. (DNA is not soluble in ice cold ethanol) therefore DNA precipitates out of the solution becoming visible as white strings in the ethanol layer.

 

Y Why we need to chill the buffer solution: As important as DNA molecules are to life, they are still extremely fragile, and break apart easily when removed from cells. Ro slow down the rate at which the DNA breaks up, we cool down the buffer solution to near freezing. Chemical reactions always take place slower in cold solutions than in warm ones, because there is a lot less energy around to make the reaction take place. Why we need to mash the onion: What we want to do by mashing the onion is to either break the cell walls (releasing the DNA into the juice) or at the very least expose the cell walls so the detergent can break them down.

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  DNA molecules are highly complicated and essentials compounds in the organism, and their method of isolation from the rest of the cell is made of indispensable yet simple stages of breaking the cell membranes, seperationg the DNA from proteins and RNAs and finally precipitating the DNA molecules. We can actually see the basic source of life after this experiment.

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Negatively charged DNA

DNA has a double helical structure maintained by hydrogen bonds. Sodium cations are essential in preserving this structure because hydrogen bonds are lost in a medium with low ionic forces.

è!Other vegetables and fruits that can be used for this lab are: Romatoes, cherries, bananas, pineapples, apples͙ Y !
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