Problem:

DNA prep protocols often include a final precipitation step with alcohol, often isopropanol, where the DNA must be kept in the alcohol, at a low temperature such as -20C or -70C, often overnight.

Required:

Question 1: What is the point of keeping it at low temperature? Is lower better? At what point do you see diminishing returns?

Question 2: What about the time? Is overnight really necessary, or would, say, an hour suffice? Do lower temperatures result in quicker precipitation?

Could anyone help me please?