5 minute DNA Extraction in a Shot Glass

Step 4 And a pinch of salt

Just add a pinch of table salt to the soapy saliva. I used less than 1/16th of a teaspoon, and that was probably too much.

So what's the deal?
Although we have freed the DNA from the cells, it's still dissolved in the solution. To get the DNA to precipitate and solidify, we need to do something about each molecule's negatively-charged phosphate backbone.

When we dissolve the table salt in the solution, some of the positively-charged Sodium ions will interact with the negatively-charged regions of the DNA molecules and effectively shield other nearby DNA molecules from their repulsive force - this will help them all aggregate and clump together in the next step.

To visualize the idea here, imagine the resistance you feel when you begin to push the south poles of two magnets together - this is sort of like what's going on between the individual DNA molecules. Now imagine inserting the north pole of a third magnet between the south poles of the first two - the resistance is reduced. The north pole of the third magnet is sort of like the Sodium ion in our solution.