 Hey everybody, Dr. O here. In this video I want to talk about the cell wall, specifically the gram positive and gram negative cell walls. I'll cover like your atypical cell walls in a separate video. So basic function of the cell wall, so remember that the plasma membrane, the cell membrane of bacteria doesn't have cholesterol in it, so without a cell wall their cells would easily rupture. We actually use that to our advantage with many of the antibiotics that are designed to weaken the cell wall, so the cells will lyse or rupture. But that's why almost all bacteria need a cell wall. So most of them are either going to have a gram positive or a gram negative cell wall, so go ahead and look at them. But first, Stiven-Libber, they're called peptidoglycan cell walls, so the peptide tells you that it's a protein component and glycan tells you there's a glucose or carbohydrate component. So I don't care about the N-A-G-N-A-M's, I don't care about the real details here, but both of them I want you to see there are a lot of similarities between the peptidoglycan and the gram positive and gram negative bacteria. But the main thing I want you thinking of is imagine like a raft, like I remember reading Huckleberry Finn when I was a kid, you know, rafting down the Mississippi or whatever. So if you were making a raft, the logs would be the carbohydrates. There's this carbohydrate backbone like these logs and the protein component, the peptide component would be the rope, like tying these logs together. So I've never built a raft to go down the Mississippi, but that's kind of how I envision it. So imagine these long carbohydrate backbones, they're actually made of chains of connecting disaccharides, but then so this long carbohydrate backbone being held together by these protein components. So that's what the word peptidoglycan means. Another term for that would be murine. So I'll put that on the screen because it's so you know how to spell it. But if you ever see this murine, it's basically saying the same thing. So that's the peptidoglycan component of it. Reason that's so important is here we're seeing a comparison of the gram positive and gram negative bacteria. As you can see right in the middle there, they both have a peptidoglycan cell wall, but they're they're wildly different. So let's just start with the gram positive bacteria. Really their only defense outside their plasma membrane is the peptidoglycan cell wall. So a thick, big, thick, strong peptidoglycan cell wall. This means the gram positive bacteria are actually better protected against mechanical issues. So I guess scrubbing them or something, but it's a pretty minor thing. And there are some very scary gram positive bacteria. Don't get me wrong. As you'll see here in just a moment, the gram negative bacteria are a much bigger problem. And that's why currently they say about 95% of the research funding is going into studying these these drug resistant or increasingly drug resistant gram negative bacteria. So let's go ahead and look at. I got a list of things here I want to talk about with with the gram negative bacteria. So so gram positive again, I don't want to belittle them, but let's focus our time on the gram negative. So both have both have cells, both have plasma membranes. But the first unique difference between the gram positive and gram negative cells is gram negative cells have very small peptidoglycan cell walls. They can be as little as one layer thick, like you see here, but they can be three or four layers. They can be several layers, but they're thin. So the gram negative bacteria have thin peptidoglycan cell walls. And you'll also notice though, between the plasma membrane and the peptidoglycan cell wall is a space. And that's this paraplasmic space it's called. And in that space, you're going to see degradative enzymes that can actually break down things that are trying to enter the cell to destroy it. Like could be some antibiotics, could be some, you know, chemical control agents. And there's also transport proteins so they can pump things out. One of the one of the scarier things about gram negative bacteria is as compounds enter the cell that would destroy it, they can be pumped right back out with these pumping proteins. So and then I know there's a lot of terminology on here, but the outer membrane, we just call it an ellipid outer membrane or an outer lipid membrane. I usually call it an LPS membrane for lipopolysaccharide. So so why is this outer membrane so important? So here's the things I want you to know. Number one, it has a very strong negative charge. And you wouldn't think that's that big of a deal, but the strong negative charge is what makes the gram negative outer membrane so dangerous, at least one of the reasons. So this strong negative charge helps gram negative bacteria evade phagocytosis, the process where phagocytic cells like neutrophils and macrophages engulf bacteria and destroy them. So it helps evade phagocytosis, but also helps evade complement. So the complement system is part of our immune system, and it can actually bore holes into microbes and also helps them helps increase phagocytosis. So the strong negative charge of this LPS or lipid outer membrane protects these gram negative bacteria from, from two key parts of your, the host immune system. All right. We also, we already talked about the fact that that paraplasmic space has some things in it that slow down our treatments and our immune system. I have a list here of things I wanted to mention that also, so what this outer membrane also is a barrier. So I just wrote a few down here detergents, heavy metals, bile salts, some of your antibiotics, the, the, the degradative enzyme lysozyme. These are all examples of things that the outer membrane keeps out. So just think about this list, this growing list of things that cannot harm gram negative bacteria like gram positive bacteria, which is why we're so concerned and looking for more, more modern treatments, right? All right. So it is the outer membrane is a barrier, but then there's one last kind of nasty piece in here and that is this lipid A. So lipid A is a toxin that's built, baked right into the outer membrane of every gram negative bacteria. Gram positive bacteria can have toxins. They're called exotoxins that are produced inside of the cell and then can be secreted out of the cell while it's living and transporting them out. Gram negative bacteria, now they, they can also have those, but I'm not going to confuse the, the issue. Gram negative bacteria have these lipid A endotoxins. So all gram negative bacteria would have the same toxin. So when this cell dies, it's actually going to dump a toxin into the environment. This toxin can lead to fever, blood clotting, dilation of blood vessels, even shock. So the, so the, so when you're killing gram negative bacteria, they're actually dumping a toxin, which means that in some cases you, you have to be careful not to be too aggressive when you're killing gram negative bacteria. If you kill them too quickly, it can actually, it can actually kill us. So that's, so just to review real quickly, gram positive bacteria think big thick peptidoglycan cell wall, their primary mode of protection is physical. So mechanical protection is the one advantage they have. Gram negative bacteria are more fragile when it comes to mechanical issues, but they have this force field around them, this outer membrane that makes them invisible to most, most phagocytes and to compliment. But also in this force field, I'm a, I'm an old Trekkie, but in this force field, you have the lipid A toxin that makes them dangerous even upon death. And then you have that paraplasmic space where they can stop things or degrade things or pump things out that would normally get in and kill the cell. So hopefully you now see why the gram negative bacteria are biggest concern. Again, there are gram positives that can do lots of damage, but the, the nightmare organisms that we're worried about now and in the future are generally going to be your gram negatives. So I think I got my whole list there of things I wanted to cover. So that is the gram positive and gram negative cell walls. I'll do a separate video on your atypical cell walls. All right. I hope this helps. Have a wonderful day. Be blessed.