Well, a protease is a protein enzyme. It's an enzyme molecule that is a protein that catalyzes the hydrolysis, the breaking of peptide bonds and peptide bonds, also known as amide bonds are the bonds that hold amino acids together in any protein molecule, in any polypeptide chain. Now, why would we need to actually break a peptide bond in the first place? 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.