the cell envelope refers to the structure Found outside our bacterial cell and this includes the actual plasma membrane it includes a cell Wall and in some cases it also includes a second membrane a second phos Bil layer as we'll see in just a moment now generally speaking we have Two different types of bacterial cells we have gram positive and gram negative and the way we differ between these Two different types of bacterial cells is by using a technique known as gram staining so Before we discuss these Two types of bacterial cells Let's discuss What the structure and the function of the cell Wall is inside our bacterial cell so the Main function of the cell Wall is to basically maintain hydr pressure to be able to resist the hydr pressure builds up within our cell now because our cytoplasmic molecules as well as molecules and ions we see that the bacterial cell is actually Found within a hypertonic environment and that means we have much more solute inside the cell than outside the cell and this means that water will flow from a low solute concentration to a High solute concentration so water will flow As A result of osmosis into that cell and as the water from the outside flows Into the inside that increases the hydrostat pressure inside our bacterial cell and What the cell Wall actually does as our hydrostat pressure increases as the turg pressure increases that cell Wall is basically able to resist that increase In hydrostat pressure and so if that cell wasn't there as our osmosis takes place and More and more water flows into that cell that cell would eventually burst If It actually did not contain that cell Wall so the cell Wall of bacterial cells basically functions to with the hydrostat pressure that exist inside our cell now in bacterial cells the cell Wall is made of a special type of molecule known as peptid glycon so Pepti means we have some type of peptide Bond and glycon means we have some type of Sugar molecule and that's exactly What our peptid glycon is peptid glycon is a polymer of Sugar as well as Amino acids that create a mesh like structure now each diacar within our peptid glycon contains several Amino acids that basically Uh connect to other Amino acids attached to adjacent Sugar Chain so to see exactly What we mean Let's take a look at the following diagram so the cell Wall is Found right outside the inner plasma membrane so Let's imagine This is the inner plasma membrane to that's side we have The cytoplasmic The fluid between our plasma membrane and this Uh cell Wall here and this is actually our cell Wall now Where exactly is our diacar unit so the entire structure of peptid glycon is composed of only Two different types of sugars we have the Red sugar and we have the blue sugar and this creates our dis unit and each dis unit contains several Amino acids in a Chain so this Purple Dash line basically correspond to our Amino acid Chain so This is our diacar unit that contains our Amino acids and these diacar create a long poly sachar Chain and these are connected As A result of a type of glyco Bond known as the Beta one4 glyco linkage now notice that we have pols Chain One poly Chain Two polyson to One another As A result of um As A result of Cross link or Cross links so Base these Amino acids connect to One another As A result of a Bridge known as the Inter Bridge so basically we have One of the Amino acids on this Chain connects to One of the Amino acids on this Chain and this is known as an Inter brid so if we for example Zoom in on this region We Get the following diagram as shown so the peptid gly consist of two types of Amino sugars or connected by Beta 144 glyco link creating a poly Chain so these are the poly Chains and these individual sugars are connected by Beta one4 glyco link now Two or more poly Chains so One and Two so let say these Two poly Chains are connected by Cross links between these Amino acids shown in Purple and these Amino acids are connected by Inter bridges so we see that the cell Walls of our entire structure within our cell envelope consist of this type of molecule known as or this type of structure known as peptid glycon and peptid glycon generally speaking contains Uh relatively large pores and these pores or holes within our cell Wall basically allow relatively large molecules to actually Pass into this region here Which is known as the perlas so the perlas actually contains different types of important enzymes different types of important Hydro enzymes that Break down different Products that end up within this Space and that helps our bacterial cell actually digest and Break down different types of molecules which then are ingested into our cell now earlier I mentioned that there are Two different types of bacterial cells so how exactly do we categor different types of bacterial cell so bacterial cells Can Be categor based on their structure of the cell envelope and we use a technique called gram staining to basically differentiate between these Two different types of bacteria cell so we have gram positive bacteria and gram negative bacteria so gram positive bacteria contain a very thick Pepti glycon cell Wall about four times as thick as the actual plasma membrane and Because of this relatively large thickness of the Pepti glycon cell Wall when we actually stain our bacteria with some type of Purple dy that Purple color remains within that cell because it cannot leave it cannot leak out of our relatively thick peptid glycon Wall and so under the microscope when we actually Take our bacteria the ground positive bacteria and stain it with the Purple dy those bacterial cells will appear Purple under the microscope so gr positive bacterial cells are cells that areed by thick cell Wall when we stain the cell with our Purple dye the thick layer of Pepti glycon prevents the Purple stain from leaking out back into our surroundings when we Wash that those bacterial cells with water so under the microscope gr positive bacterial cells appear Purple now in both types Of these Uh cells the perlas Uh the per plasm Space as i mention earlier basically contains important Hydro enzymes that Break down different types of molecules that are then ingested Into the cell so that the cell can use them to basically function properly now Let's move on to the gram negative bacteria so the Main difference between gram positive and gram negative is the thickness of our cell Wall of that peptid glycon layer so these bacteria cells are character by a thin peptid glycon cell Wall now because the cell Wall is so thin when we actually stain our bacterial cells with our Purple dye because the layer is so thin that Purple dy can easily Wash out when we Wash it with water so that means under the microscope all that Purple Die will be removed after washing and our bacterial cell will appear Pink on under the microscope now on top of having a thin Pepti glycon layer the other difference between gram negative and gram positive is that in gram negative we also have a second phosphor by layer Found right outside our Pepti glycon cell Wall and this phosphor by layer is more per than our inner plasma membrane so it actually allows relatively large molecules to Pass through that phosphor byer for example it allows Sugar molecules to Pass right through and the Sugar molecules because the actual Wall contains pores will end up within this section and then those Sugar molecules Can either Be broken down by the Hydro enzymes or They Can Be ingested directly into our cell Wall now another difference between our gram negative and gram positive is because our gram negative contains this second phosphor PID by layer that phosphor Bil layer contains special types of molecules known as Uh lip poly so it contains Lipo polyacril off by different types of drugs as well as antibodies Found within our Body so basically these types of bacteria can resist the different drugs that we develop in the laboratory to kill off the different type of bacteria cells Found in our Body so basically One important part that our cell envelope contains is the peptid glycon so basically we can develop different types of drugs that actually Break The Cross links between our poly Chains within the peptid glycon and that Kills off our bacterial cell other different types of drugs that We can use can also Break our bonds between the diacar between this Red and this Blue and that can also kill off our cell mem Uh our cell because Once we Break that cell Wall it can No longer resist that hydr pressure that our internal environment of the cell actually contains and if we Break our cell Wall that bacterial cell will actually burst now Let's look at our description of the gram positive and our gram negative cell envelope so the cell envelope of gr positive basically contains the inner membrane the phosphor membrane and a relatively thick Pepti glycon cell Wall now the gram negative contains this inner membrane a thin cell Wall and an outer membrane and the outer membrane contains these poly which are base or Uh Lipo poly which are basically the lipids attached to long Chains of sugars and these sugars create a net negative charge Around the entire cell Uh bacteria cell and That protects it from different types of drugs now we also have a section that the cell Wall to our outer membrane and this is our poly our Lipo proteins so these Brown regions are liper proteins also known as browns lip proteins and the entire or the Main function Of these Brown liper proteins 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 the cell envelope contains our cell Wall Which is made of a material known As A peptid glycon and it also contains the inner plasma membrane in some cases we also have an outer plasma membrane basically our gr positive bacteria contain a very thick Pepti glycon cell Wall and that allows the Purple dye to remain inside that cell and that's exactly why on the microscope these types of bacterial cells appear Purple but Because of the thin cell Wall of our gram negative that Purple dye Can Be easily washed off and so these gram negative bacterial cells appear Pink Under our microscope now One of the Main functions of the cell Wall made of Pepti glycon is to basically resist that hydrostat pressure that turg pressure that builds up within that cell As A result of the hypertonic environment now if we examine the outer membrane of our gram negative bacterial cells we see that we have these Lipo poly saac which Play a very important role in creating a protective barrier around that bacterial cell