And the PH is a factor that can influence the many different types of biological processes that take place inside our body. As we'll see the next lecture, for example, the PH can determine what the final structure is of biological molecules such as proteins and DNA. Now, in this lecture, we're going to focus simply on what an acidbased reaction is. We're going to remember what PH is and we're going to remember what acidic and basic solutions are. So let's begin by recalling what an acid based reaction is. So an acidbase reaction is a reaction in which we exchange an H plus ion between two different molecules.