Now, we also have a section that connects the cell wall to our outer membrane, and this is our poly, our lipoproteins. So these brown regions are lipoproteins, also known as browns lipoproteins. And the entire or the main function of these brown lipoproteins, is to actually hold together via covalent bonds, the thin cell wall as well as our outer membrane. So we see that when we discuss bacterial cells, there are two main categories of bacterial cells. We have gram positive and gram negative. And the way we differentiate these two different types of bacterial cells is by the cell envelope.