The Dna Extraction Essay Example for Free

The Dna Extraction Essay 1. The salt contributes positively charged atoms that neutralise the normal negative charge of DNA. Salt is used at a high molarity due to the fact that it precipitates all of the proteins out. DNA is insoluble in low molar salt solutions but soluble in low molar salt solutions thus keeping the DNA in solution. 2. blending the onion will homogenize the mixture and it helps with the breakdown of the cell walls. Blending saves one the time and effort of using a motar and pestle, however it may break a lot of the DNA which is not favourable as one needs a lot of DNA for the extraction. 3. The enzymes in the soap are used to break down the lipid (fat) molecules of the cells nuclear membranes releasing the contents of the cell crucially including the DNA. These enzymes in the soap are what break down grease while washing dishes. 4. The DNA does not dissolve in this alcohol but rather pushes up through and out of the solution or precipitates. It is less dense than water or cell scum which is what settles to the bottom of the glass so it floats up into the alcohol layer, where you see it as a snotty, string-like substance, with small bubbles formed on it. 5. Because protein is stored in them for the nutrition of the new plants. 6. It is too small to be seen with the naked eye. What you extracted is millions of strands of DNA. In addition to that, whilst the substance was heated, the DNA got denatured which results in it looking more like a ladder than a helix. 7. Most of the DNA extracted during this proccess comes from the nucleus of the cell. AIM: The purpose of this experiment is to extract DNA from a variety of cells (Onion cells in particular) and see DNA molecules. This will show that, contrary to popular opinion, DNA is not just found in blood cells, but in a variety of tissues. Prior knowledge should include the fact that cell membranes are layers of lipids, or fat molecules, that DNA is found in the nucleus of a cell, and that enzymes speed up chemical reactions. HYPOTHESIS: DNA is present in the cells of all living organisms. METHOD: 1. Prepare two water baths one at 60Â °C and another filled with ice and water, around 4Â °C. For the hot water bath, a large metal pot can be used along with a thermometer with an appropriate temperature range. For the ice bath, a mixing bowl filled with ice and water works well. 2. For each onion, make a solution consisting of 10 ml of liquid dishwashing detergent and 1.5 g of table salt. Put in a 250 ml beaker and emulsify. 3. Add distilled water to make a final volume of 100 ml. Dissolve the salt by stirring slowly to avoid foaming. 4. Coarsely chop one large onion with a food processor or blender and put into a 1000 ml mixing bowl. For best results, do not chop the onion too finely. The size of the pieces should be like those used in making spaghetti. It is better to have the pieces too large than too small. 5. Cover chopped onion with the 100 ml of solution from step 2. The liquid detergent causes the cell membrane to break down and dissolves the lipids and proteins of the cell by disrupting the bonds that hold the cell membrane together. The detergent causes lipids and proteins to precipitate out of the solution. Salt enables nucleic acids to precipitate out of an alcohol solution because it shields the negative phosphate end of DNA, causing the DNA strands to come closer together and coalesce. 6. Put the measuring cup in a hot water bath at 60Â °C for 10-12 minutes. During this time, press the chopped onion mixture against the side of the measuring cup with the back of the spoon. (Do not keep the mixture in the hot water bath for more than 15 minutes because the DNA will begin to break down.) If using a large metal pot for water bath, remove the pot from the stove before placing the onion-containing measuring cup inside—the procedure is safer if the pot is off the burner. Cont inue to monitor temperature of water bath and make adjustments as needed. 7. The heat treatment softens the phospholipids in the cell membrane and denatures the DNAse enzymes which, if present, would cut the DNA into small fragments so that it could not be extracted. 8. Cool the mixture in an ice water bath for 5 minutes. During this time, press the chopped onion mixture against the side of the measuring cup with the back of the spoon. This step slows the breakdown of DNA. 9. Filter the mixture through a #6 coffee filter or four layers of cheese cloth placed in a strainer over a 4-cup measuring cup. When you filter the onion mixture, try to keep the foam from getting into the filtrate. It sometimes filters slowly, so you might want to put the whole set up in the refrigerator and let it filter overnight. 10. Dispense the onion solution into a test tube. The test tube should contain about 1 teaspoon of solution or be about 1/3 full. For most uniform results among test tubes, stir the solution frequently when dispensing it into the tubes. There is not an adva ntage to dispensing more than one teaspoon of solution into a test tube. The solution can be stored in a refrigerator for about a day before it is used for the laboratory exercise. When the solution is removed from the refrigerator, it should be gently mixed before the test tubes are filled. 11. Add cold alcohol to the test tube to create an alcohol layer on top of about 1 cm. For best results, the alcohol should be as cold as possible. The alcohol can be added to the solution in at least three ways: (a) Fill a pasteur pipette with alcohol, put it to bottom of the test tube, and release the alcohol. (b) Or, put about 1 cm of alcohol into the bottom of a test tube and add the onion solution. (c) Or, slowly pour the alcohol down the inside of the test tube with a pasteur pipette or medicine dropper. DNA is not soluble in alcohol. When alcohol is added to the mixture, all the components of the mixture, except for DNA, stay in solution while the DNA precipitates out into the alcohol layer. 1 2. Let the solution sit for 2-3 minutes without disturbing it. It is important NOT to shake the test tube. You can watch the white DNA precipitate out into the alcohol layer. When good results are obtained, there will be enough DNA to spool on to a glass rod, a pasteur pipette that has been heated at the tip to form a hook, or similar device. A wooden skewer or nut pick (small metal rod with curved tip) may also work well for spooling DNA if Pasteur pipette is unavailable. DNA has the appearance of white mucus. CONCLUSION: With these findings we can conclude that DNA is present and can be found in the cells of all living organisms and not just in those of the human body.