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Onion Dna Extraction

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ANSWERS TO STUDENT QUESTIONS
1. Buffer: A solution that will maintain a constant pH, chelate metal ions and generally maintain an environment that will prevent disruption of the experiment. Precipitate: The solid which is visible when a substance becomes insoluble from a solution. Filter: To separate by passing a mixture through a selective membrane. Emulsify: To physically break up lipid into smaller lipid globules. 2. To maintain an environment in which the DNA will not be degraded and to help separate the DNA from other cell components. Tris maintains a constant pH. EDTA chelates metal ions. NaCl provides Na+ ions that will block negative charge from phosphates on DNA. 3. Negatively charged phosphates on DNA cause molecules to repel each other. The Na+ ions will form an ionic bond with the negatively charged phosphates on the DNA, neutralizing the negative charges and allowing the DNA molecules to come together. 4. Any non-starchy vegetable should work. Potatoes would not work well. 5. Answers will vary.

6. DNA in cells will absorb UV light. When it does it can be damaged. If the damage occurs in a cell cycle gene, then growth may become uncontrolled leading to skin cancer.

STUDENT PAGE 1
DNA Isolation from Onion
INTRODUCTION The process of isolating DNA from a cell is the first step for many laboratory procedures in biotechnology. The scientist must be able to separate the DNA from the unwanted substances of the cell gently enough so that the DNA is not broken up or shredded. The procedure you will be doing is a modification of the "Marmur" preparation which is used worldwide in biotechnology laboratories. A "Filtrate" is made of onions treated with salt, distilled water and detergent(SDS). An onion is used because it has a low starch content which allows the DNA to be seen more clearly. The salt shields the negative phosphate end of DNA which allows these ends to come closer so they can precipitate out of a cold alcohol...

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