I saw a cool video today of a DIY DNA isolation ‘protocol’. In the video you see a young lady extracting DNA from her cheek cells by using household ingredients. However I was a bit disappointed they did not add what chemical performs which task. Therefore I decided to make a list of the ingredients they used with their roles in the experiment and of course a link to the video.
The usual laboratory protocol involves five steps for DNA isolation for mammalian or plant cells.
- Homogenisation – the disruption of tissues usually done by soaps, e.g. SDS (sodium dodecyl sulphate) which is found in body soaps, hand soap, shampoo, tooth paste and in this case, dishwasher soap.
- The enzymic removal of protein and RNA – this is a bit too complicated to do with household objects. This is where she uses salt which causes the proteins that are usually bound to DNA to fall off due to difference made in their net charge.
- Phenol-Chloroform extraction – this removes traces of proteins by forming two separate layers like water and oil, one of which containing the DNA. The DNA will be able to dissolve in the aqueous layer and the proteins will precipitate into the ‘organic’ layer. This is of course a bit risky to do at home as chloroform tends to be … rather poisonous.
- Precipitations of the DNA – this is done by the alcohol, in this case isopropyl alcohol which causes the DNA to precipitate as it is no longer able to be soluble in water. (Usually there would be a centrifuge step etc. here to force the DNA to go down into the tube and ‘stick’ to the bottom. This makes it able to remove all the remaining water, alcohol and salts. This is followed by a few washing steps to make sure it’s as pure as possible.)
- Solubilisation in an appropriate volume of buffer with a pH of 7.5 – now it should be able to be stored. Yet again being able to store stable DNA with household products is not possible (as of yet, if you’re optimistic).
So basically as a recap, soap to disrupt the membranes, salt to get rid of excess proteins, and after letting everything float to the bottom, add the alcohol to precipitate your DNA.
The video in question;
““Commonly Used Techniques in Molecular Cloning,” Appendix 8, in Molecular Cloning, Volume 3, 3rd edition, by Joseph Sambrook and David W. Russell. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, USA, 2001″
“Practical Skills in Biomolecular Sciences,” 3rd edition, by Reed et al. Pearson. p369