And these proteins can be broken down and recycled into amino acids. So we have many different types of proteins that exist as enzymes, and these enzymes must be inactivated. And sometimes, to inactivate an enzyme, we proteolytically cleavage, we destroy it, and then we recycle those amino acids. Now, some proteins can be damaged, for example, the oxidation processes. And when proteins are damaged, we have special types of complexes that exist inside our cells, as we'll talk about in the next lecture, that utilize a protein known as Ubiquitin and a complex known as the proteosome complex that essentially breaks down and degrades damage or misfolded proteins into their amino acid constituents. And then those amino acid constituents can be utilized by the cell to carry out some type of process, to build some type of important molecule.