Dna Extraction from onions

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- Identify possible sources of errors:

- Improper measurements of detergent.

- Improper measurements ofsodium chloride.

- Chopping the onion too finely.

- Heating the onion for too long or at too high of a temperature.

- Not pressing the onion against the walls of the beaker.

- Loss of DNA during spooling and transfer

- Steam bath unstable temperature.

- Improper ethanol concentration.

- Suggestions on improving the experiment:

- Try adjusting the amount of water, salt or soap.

- If there is too much water, the amount of DNA may not be concentrated enough to see.

- Don't stir too vigorously when mixing in the soap, because this can break up the long DNA strands into small pieces, and make them harder to see.

- Keeping it cold will prevent cellular enzymes from breaking down the DNA. Use cold water, and after adding the soap, place the test tube on ice while it is sitting for 5 minutes.

- You can also add a pinch of meat tenderizer along with the salt. Meat tenderizer will inhibit the action of the cellular enzymes and help to keep the long DNA strands intact.

Conclusion

The strands of DNA from the onions can be seen floating on the top layer of the mixture and is extracted successfully. Hypothesis is accepted.

Questions:

- The motion and physical force of the blender will break down the cell wall, cell membrane and nuclear membrane of plant cells and allowing the DNA to be released from the cell.

- Salty water enables nucleic acids to precipitate out of an alcohol solution because it shields the negative phosphate end of DNA, causing them to come closer together and coalesce.

- The detergent will break down further and emulsify the lipids and proteins of the cell. It does this by disrupting the polar interactions that hold the cell membranes of each cell to release the DNA.

- Heat softens the phospholipid on cell wall and membranes and enhances the action of the detergent. Heat also denatures enzymes DNase which, if present, would cut the DNA into small fragments too small to be extracted.

- Using ice-cold ethanol and ice-cold water increases the yield of DNA. Low temperatures protect the DNA by slowing down the activity of enzymes that could break it apart. A cell’s DNA is usually protected from such enzymes (DNases) by the nuclear membrane which is disrupted by adding detergent. DNases in the cytoplasm would destroy the DNA of viruses entering the cell. Cold ethanol helps the DNA to precipitate more quickly.

- Chilled ethanol is added because DNA is soluble in water. The DNA does not dissolve in alcohol and therefore forms a precipitate (solid) layer where it contacts the cold alcohol. This separates the DNA from other macromolecules and from the cell contents.

References

Biologyjunction.com,. (n.d.). extracting DNA. Retrieved 19 August 2014, from http://www.biologyjunction.com/extracting_dna.htm

Learn.genetics.utah.edu,. (2014). Frequently Asked Questions. Retrieved 19 August 2014, from http://learn.genetics.utah.edu/content/labs/extraction/howto/faq/

Nuffieldfoundation.org,. (2011). Extracting DNA from living things | Nuffield Foundation. Retrieved 19 August 2014, from http://www.nuffieldfoundation.org/practical-biology/extracting-dna-living-things