Science Buddies: "Ask an Expert"

My science fair project is to extract dna from very small bacteria with the help of soap and alcohol (isopropyl). The dna is precipitated in very small forms. But how can i extract that dna from solution? Or how can i stain particularly dna with some household product?

Hi,

The bacteria may be small, but their DNA is quite large. If you haven't already done so, check Scibuddies for projects involving DNA extraction from various things. Here's one in which DNA is isolated from strawberries: https://www.sciencebuddies.org/science- ... #procedure

To isolate DNA from bacteria you need a fairly large number. Your culture should be quite cloudy looking. Adding detergent to the bacterial suspension will cause it to clear because the detergent dissolves the cell membranes. Your procedure should also call for the addition of a certain amount of table salt which improves the yield of DNA.

Now slowly add two volumes of cold isopropanol to the tube containing the dissolved [the correct term is 'lysed'] bacteria. where the alcohol meets the bacterial solution you will see a whitish layer. That contains DNA, RNA and some protein. Now take a thin glass or plastic rod and gently put it down through the alcohol past the white layer. Twist the rod around and around in the layer and you will see the DNA wind around it. It is not completely pure as there is some protein and RNA mixed with it but it is mostly DNA. This technique is called DNA spooling. The DNA can be rinsed in isopropanol and dissolved in a small amount of water.

If you want to watch how the procedure is done, take a look at this video from GenomeTV: https://www.youtube.com/watch?v=hOpu4iN5Bh4

If you have any more questions, we'll be happy to help.

Sybee

Thts great. But the amount of bacteria is limited and for limited DNA how can i stain that dna?

Why is the amount of bacteria limited? You can grow them on a Petri dish or in liquid culture until you have enough to do spooling.

It would be helpful to the experts if you would take the time to explain exactly what you are doing in your project so we have all the information. Isolating DNA from a small sample and running it on an agarose gel containing ethidium bromide to visualize it is a simple procedure in a molecular biology research lab, but not something you can do at home or even in most high school labs.

Tell us the purpose of your science project, what bacteria you are using and why and we will offer suggestions.

Sybee