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DNA Extraction Essay

Much can be learned from studying an organisms DNA. The first step to doing this is extracting DNA from cells. In this experiment, you will isolate DNA from the cells of fruit. Materials (1) 10 mL Graduated Cylinder(2) 100 mL Beakers15 cm Cheesecloth1 Resealable Bag1 Rubber Band (Large. Contains latex pleasewear gloves when handling if you have a latex allergy).Standing Test TubeWooden Stir StickFresh, Soft Fruit (e.g., Grapes, Strawberries, Banana, etc.) ScissorsDNA Extraction SolutionIce Cold EthanolYou Must ProvideContains sodium chloride, detergent and waterFor ice cold ethanol, store in the freezer 60 minutes before use. Procedure If you have not done so, prepare the ethanol by placing it in a freezer for approximately 60 minutes. Put pieces of a soft fruit into a plastic zipper bag and mash with your fist. The amount of food should be equal to the size of approximately five grapes. Use the 10 mL graduated cylinder to measure 10 mL of the DNA Extraction Solution.

Transfer the solution from the cylinder to the bag with the fruit it in. Seal the bag completely. Mix well by kneading the bag for two minutes. Create a filter by placing the center of the cheesecloth over the mouth of the standing test tube, pushing it into the tube about two inches, and securing the cheesecloth with a rubber band around the top of the test tube. Cut a hole in the corner of the bag and filter your extraction by pouring it into the cheesecloth. You will need to keep the filtered solution which passes through the cheese cloth into the standing test tube. Rinse the 10 mL graduated cylinder, and measure five mL of ice-cold ethanol. Then, while holding the standing test tube at a 45 angle, slowly transfer the ethanol into the standing test tube with the filtered solution.

The color has been enhanced by dying the fruit with a substance that glows under black light.DNA will precipitate (come out of solution) after the ethanol has been added to the solution. Let the test tube sit undisturbed for 2 – 5 minutes. You should begin to see air bubbles form at the boundary line between the ethanol and the filtered fruit solution. Bubbles will form near the top, and you will eventually see the DNA float to the top of the ethanol. Gently insert the stir stick into the test tube. Slowly raise and lower the tip several times to spool and collect the DNA. If there is an insufficient amount of DNA available, it may not float to the top of the solution in a form that can be easily spooled or removed from the tube. However, the DNA will still be visible as white/clear clusters by gently stirring the solution and pushing the clusters around the top. Post-Lab Questions What is the texture and consistency of the DNA DNA is viscous and greasy. Why did we use a salt in the extraction solution High salt makes DNA less soluble in water. In order to dissolve, the water needs to interact with the DNA.

Since DNA is quite large, it needs to interact with lots of water for this purpose. When you add salt, the water preferentially interacts with the salt (its small, and can move around in solution easier than the DNA can). This makes it so there is less water available to interact with the DNA and it becomes less soluble. Is the DNA soluble in the aqueous solution or alcohol DNA is less soluble in an alcohol such as isopropanol than it is in water. This is because alcohols are non-polar, whereas water is polar. The polar water molecule is much better at distributing the negative charge on DNA, causing it to remain in solution. However, since alcohol is non-polar, the negatively charged molecules of DNA tend to group together, forming clumps, which precipitate out of the alcohol solution.

What else might be in the ethanol/aqueous interface How could you eliminate this When you precipitate the solution with cold ethanol 70 you would have a mix of DNA, RNA and some soluble salts. You should be able to centrifuge again so the DNA/RNA forms a pellet and drain the liquid out. Which DNA bases pair with each other How many hydrogen bonds are shared by each pair How is information to make proteins passed on through generations Watch the following Virtual Lab demonstrating DNA Extraction. In this experiment, how do the Lysis Solution and the Salt Solution vary by function Identify one step which was included in the Virtual Lab which was not required in the hands-on experiment. Then, identify one step which was included in the hands-on experiment, but not the virtual lab.


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