Well, for instance, if we ingest some food particle that is a macromolecule for instant protein, then we have to be able to break down that food protein molecule into its individual constituent amino acids. So that once we have those amino acids, we can either use the amino acids to actually form, let's say, ATP molecules, or we can also use the amino acids to actually form brand new proteins and brand new enzymes. Now, the second reason as to why we need to be able to break a peptide bond is because our cells actually need to be able to recycle protein molecules. For instance, if, let's say, a cell needs to decrease the number of protein channels found in the cell membrane, it has to be able to remove those protein channels and then digest those protein channels. And so inside the cells, we have these digestive enzymes in the same way that we have digestive enzymes inside our small intestine as well as inside our stomach. And these digestive enzymes are proteases.