And what the biological purpose of these molecules is, is to protect those cells from different types of foreign pathogenic DNA molecules. For instance, if a virus that carries DNA infects a bacterial cell, the bacterial cell can protect itself by using these restriction enzymes. And what these restriction restriction enzymes do is they bind onto that viral DNA molecule and they cleave it. They cut it up into smaller nonfunctional fragments. Now, biochemists can actually extract and clone these restriction enzymes from these bacterial cells and prokaryotic cells, and we can use them for a variety of different purposes as we'll discuss in the next several electros. So there are four purposes I've listed on the board.