What is an enzyme?
According to encyclopedia.com, enzymes are biological catalysts, or chemicals that speed up the rate of reaction between substances without themselves being consumed in the reaction. As such, they are vital to such bodily functions as digestion, and they make possible processes that normally could not occur.
So, a catalyst is simply anything that speeds up the process of something else. In our bodies enzymes help with all sorts of things like copying out DNA, energy production and extracting nutrients from food through. Pepsin and trypsin are particularly helpful in digesting dietary proteins.