We also have to remember the second law of thermodynamics which basically describes the fact that in any real biological process the change in entropy of the universe is always positive, it always increases. So we also have to consider the temperature and the conditions under which a reaction is taking place because under certain conditions a reaction might be spontaneous but under other conditions the reaction might not be spontaneous. And so we have to consider the gifts free energy of our reaction. 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.