Onion DNA extraction.?

Question

So, if anyone has ever done that experience.
Please explain those steps.

1-What does blending the onion do?
2-What does soap and NaCl (table salt) does?
3-Why do we have to heat the onion at 65 C for 15 minutes?
4-Why put the mixture on ice for 5 minutes right after?
5-Why filter the mixture? (Sounds stupid but...)
6-Why does putting ethanol in the mixture separate the DNA of the onion from it's source?

Thank you.
I know, I didn't get any of my experimentation but the teacher said we had to search the web to understand it.
That's what I'm doing.
Thank you.

Brown Sugar: Err I think it's because we want a purer DNA but I have to do an assignment which explains every step in detail (in french, so it's not plagiarism) so I like your answer but it doesn't help that much.

Answer 1

blending the onion breaks up the molecules, and makes it easier to extract the DNA everything just helps the DNA separate... you probably do more than u really have to... they just waist ur time makin it more complex than it probably has to be... but google it buddy! google knows all!

Answer 2

Onion Dna Extraction Lab

Answer 3

As a start, in order to extract DNA from cells, the cells must first be broken open. The DNA must then be separated from the cell debris and the other materials, like proteins and RNA, while being protected from being broken up by enzymes called DNAses. Finally, the DNA must be removed from solution; the old standard method of doing this is by precipitating it from solution by making the solution very salty and about 2/3 alcohol (often Ethanol). At that point, with the DNA floating around in the solution, but not dissolved in the liquid, it can either be picked up using a glass rod, or simply centrifuged down and the pellet washed off and resuspended in a protective buffered solution.

Answer 4

please understand the mentioned steps will isolate only crude DNA.
1) blending the onion will homogenize the mixture. (i would say blending saves time from using a motar and pestle but it may break a lot of DNA as u need to be very gentle with DNA extractions)

2) the soap (detergent) helps to lyse the tough cell wall of the cells. (sodium do decyl sulphate is a better option for a detergent.) NaCl is used (in higher molarity because it will precipitate the proteins out)DNA is insoluble in low molar salt solutions but soluble in high molar salt solutons thus keeping the DNA in solution.

3) heating to 65C is not really necessary but just ensures that proteins are precipitated. this doesnt damage the much as it is very stable upto 75C

4)instant cooling helps to quicken the process of cooling.

5) filter the mixture because now that u have precipitated all unwanted stuffs like proteins from the mixture u want a clear filtrate with only ur DNA in it.

6) abt twice the amount of ethanol is required to precipitate the DNA out. ie if u have 10 mL of filtrate then u need 20 mL of chilled ethanol. the ethanol lowers the isoelectric point of DNA thus precipitating it out. note that this step has to be done at 4C or in a ice bath. u will see thread like DNA precipitaing out. u can spool it with a thin cappillary. most students think that the threads they see are double stranded DNA but in actual they are DNA attached to nucleosomes. yes i did say that u precipitate the proteins but not all are precipitated.
this is a very crude method to extract DNA but it is fun none the less.
u may have to dissolve this extracted DNA in DPA (diphenylamine) frshly prepared stock and boil for 20 mins to get a purple colour of beta hydroxy levulinic acid. this reaction is not specific for DNA but for pentose sugars (deoxyribose is a pentose sugar). this confirms that whatever u extracted was DNA.