DNA Extraction from Onion Cells

Analyzing and Interpreting

1.The purpose of cutting the DNA into very small pieces was to break the cell walls of the onion cells so that the DNA will have a way to exit the cell.

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Final

Product:

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4.Appearance of the

Extracted DNA:

• DNA looks like long clearish white thin strands that are wrapped around the glass rod after it has been taken out of the filtrate solution.(see image 8)
• While the DNA is still in the solution, it is in the form of a precipitate. This is because the DNA is insoluble in alcohol(isopropanol). The alcohol caused the DNA to clump together in a concentrated area.(see image 9)

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2. Effects of the

extraction solution

on DNA:

• The solution turned cloudy and foamy.
• The soap in the extraction solution is polar and so are the cell membranes of the onion cells. Therefore the soap was able to pass through the cell membrane and the nuclear membrane. The soap destroyed the lipid bi-layer which caused the DNA to be released (Hays, n.d.).
• The extraction solution also helps to denature the histone proteins which the DNA is spooled around. (Carboni 2007).

6.When you place some of the DNA sample in water and stir it, the DNA will dissolve in the water. This is because of the fact that we understand that water is a polar molecule so according to the "like dissolves like" rule, we know that DNA must be polar in order to be able to dissolve in water. Therefore DNA is polar and water soluble.

(Extract DNA From Anything Living, n.d.).

In our lab, this step was slightly altered due to the fact that the extraction solution contained water and we added water as we were chopping the onion. However, there was not enough water added in this lab to completely dissolve the DNA which is why we were able to view it.

DNA Extraction from Onion Cells

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6. When isopropanol was added to the liquid that passed through the filter (the filtrate), it caused the DNA to form a precipitate that was concentrated between the filtate and the isopropanol. This is a result of the fact that DNA is insoluble in alcohols such as isopropanol. This precipitate was displayed clearly in the lab.(See image 10)

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3.Effect of the filtering process on DNA molecules:

• used to collect the liquid (cytoplasm & water) filled with DNA in a test tube.
• used to separate the onion tissues and other cellular products from the DNA so that it can be discarded.

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7. DNA and Litmus Paper

• When the DNA sample was tested with litmus paper, the paper did not change colour at all.(see image 11)
• The DNA sample was supposed to change the litmus paper red because DNA is an acid (made up of nucleic acids - Deoxyribonucleic acid) and acids are supposed to turn blue litmus paper red.
• Sources of error: not enough DNA on the rod to rub on the litmus paper - we had difficulty getting even a single DNA strand onto the rod. Also, the extraction solution was still on the rod (and the extraction solution is basic) so this could have been the reason why the litmus paper did not turn red.

By: Isabella Mizzi

Concluding and Communicating

8. Characteristics/features of DNA:

• acidic, therefore it was supposed to turn the blue litmus paper red.
• soluble in water.
• insoluble in isopropanol.
• appearance: long and thin clearish white strands.
• forms a precipitate when mixed with isopropanol.

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11.Roles of the following substances

used in this investigation:

• baking soda: acts as a buffer to keep the pH at an optimal level for DNA (pH of about 7) so that the DNA doesn't denature.(Isolation of Fruit DNA, n.d.)
• shampoo: is non-polar like the onion cell membrane, so the shampoo can enter the cell membrane and break down the lipid walls of the cell membrane - releases all contents of the cell including DNA (Carboni, 2007).
• salt: denatures the histone proteins that the DNA is spooled around. This allows the DNA to uncoil (Carboni, 2007). DNA also has a negative charge and the salt helps to neutralize this charge which allows DNA to remain in its double helix shape(Isolation of Fruit DNA, n.d.).
• isopropanol: DNA is not soluble in isopropaol. This causes the DNA to form a precipitate when mixed with isopropanol, which makes it visible to the naked human eye (Isolation of Fruit DNA, n.d.).

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