Now, another factor that we haven't yet focused on is the PH of a solution. So in the next several lectures we're going to discuss how the PH of a solution can also influence the pathway of the reaction and the final structure of that biological molecule. So to demonstrate how these factors can influence a particular biological reaction let's take a look at a common reaction the formation of a double helix of DNA. So inside every nucleus of every cell in our body we have DNA. Now, the DNA doesn't exist as a single strand. It exists as a double helix.