we'll come back to chapter four in this third video we're going to be covering the components and functions of the endomembrane system so the endomembrane system where Endo refers to inside or within the cell is a group of membranes and organelles that work together to modify package and transport lipids and proteins the endomembrane system includes the following components so it includes the nuclear envelope which we saw earlier lysosomes and vesicles and a few things we haven't talked about yet including the endoplasmic reticulum and Golgi apparatus it also includes the plasma membrane and we're going to see the membranes of the endomembrane system are interchangeable so what we're going to see is that if I'm looking at something like a membrane or secretory protein meaning these are proteins that are going to end up in the cell membrane or be secreted out of the cell their synthesis begins at the rough ER the rough endoplasmic plasmic reticulum specifically through the use of the ribosomes that are attached to the rough ER sometimes the rough ER also modifies proteins so I see this green protein here looks like a little peanut and it's being synthesized and Modified by the rough ER and then it buds out it comes out of the rough ER through this vesicle and the next place it's going to go is to the Golgi apparatus it enters the Golgi at the CIS face of the Golgi apparatus this is the side of the Golgi that faces the inside of the cell or faces the rough ER and the Golgi will further modify this protein through attachment of perhaps other carbohydrates this protein will eventually exit the other side of the Golgi the trans face and then you can see that it has been modified the vesicle that comes out of the trans face of the Golgi will eventually fuse with the cell membrane and then you can see that the protein and the carbohydrate that's attached to it will be facing the outside of the cell so what is the endoplasmic reticulum it's really a bunch of interconnected membranous sacs and tubules and the membrane of the ER is actually continuous with the nuclear envelope and that's why you'll always find the ER next to the nucleus so if I look closely I see two types of ER I have my rough ER that I saw earlier in the previous slide as well and it's called rough because on the surface we have ribosomes attached to the rough ER the other type is continuous with a rough ER and we call it the smooth ER because there are no ribosomes attached to the surface of these membranes they have two different functions between the rough and smooth ER the rough ER that's its function is primarily to produce proteins through the ribosomes that are attached to its surface it can also sometimes modify those proteins the smooth ER though its primary purpose is to make lipids for us the space between the membranes is called the Lumen or sometimes we call it the cisternal space here's a closer look at the rough ER and remember earlier in a previous video I talked about ribosomes and however there are two types there are the ribosomes that are attached to the rough ER and these make proteins that are destined to either leave the cell they're going to be secreted leaving the cell or they're going to be incorporated into other membranous structures free ribosomes on the other hand free ribosomes that are floating around in the cytoplasm of the cell they'll just be floating around not attached to the rough ER those are going to make proteins that are destined to stay some are in the cytoplasm of the cell so for these ribosomes that are attached to the rough ER they're going to be sometimes modified and the modification of the proteins happens in the Lumen within the membranous sacs these modified proteins are either going to leave the rough ER and eventually be incorporated into some kind of cell membrane structure like another organelle or they're going to be secreted from the cell and I like the picture down here I can see this giant nucleus this is a transmission electron micrograph so a picture using a transmission electron microscope and I see these the rough ER I can see lots of membranes and some dots on them which represent the ribosomes and although it's not their primary function the rough ER can also make phospholipids for different membranous structures within the cell if these phospholipids and the proteins we talked about in the previous slide are not going to be staying inside the rough ER they're going to actually eventually reach their destinations through transport vesicles that come out of the rough ER membrane and then usually their next stop is the Golgi apparatus in contrast to the rough ER the Smoothie yard doesn't really have any ribosomes attached to its surface and its main function is to synthesize lipids although it can also produce things like carbohydrates and some of our steroid remember these are nonpolar hormones or water fearing hormones the Ser or smooth ER can also detoxify some of the medications that we take they can detoxify poisons and in some tissues they are involved in the storage of calcium and this is especially true in our human muscle tissues this is a picture of the human muscle cell specifically a type of muscle known as skeletal muscle that allows contraction and movement of our body parts these have a cell membrane we call it the sarcolemma in skeletal muscle cells and then we also have our Sr our sarcoplasmic reticulum so this is the equivalent of the smooth ER that we find in other tissues or other cells and in our muscles these are responsible for storing a ton of calcium that is involved in muscle contraction all right so earlier when we were talking about the rough ER also shown here rough endoplasmic reticulum and I know that proteins are produced and sometimes Modified by the rough ER then they need to go somewhere else they need to go to the Golgi next if they're going to be secreted or exported from the cell and I know they enter from the CIS side of the Golgi and then they exit through the trans side but what does the Golgi actually do the Golgi apparatus or sometimes we say Golgi body is the Post Office of the cell so it's really great at sorting packaging and adding address tags to these proteins so they get to the right place they get to the right destination so imagine the rough ER makes a bunch of different proteins all of the time a set of protein a a bunch of proteins that are packaged as protein a in a vesicle maybe another that are called protein B they go to the Golgi and the Golgi repackages all the proteins so they're all grouped together like these could all be the group a proteins and they'll have an address tag on these proteins so they know where to go next lysosomes can also be produced here so remember lysosomes from our previous video lysosomes these look like a generic vesicle but they contain digestive enzymes and they have an acidic internal environment so the production of lysosomes happens through through this process as well lysosomes those digestive enzymes are produced at the rough ER then they go to the Golgi for further modification and also tagging so that these vesicles know where to end up if I look down here it looks like I have another image produced through transmission electron microscopy and I see a series of flattened sacs here that are my Golgi so here's a look at the original picture with the Golgi apparatus and again remember the CIS face is the receiving side of the Golgi where they receive vesicles coming from the rough ER and the exit where the vesicles exit after modification that is the trans face so vesicles from the ER are going to enter the space and exit the trans face and as they go through the Golgi remember this is the Post Office of the cell they're further modified so they can be sorted according to where they're going to go next all the proteins going to the same or similar regions should be repackaged together during the sorting and and tagging process the Golgi will usually add different types of sugar molecules to the protein or whatever molecules being modified at the moment so these are short carbohydrate chains remember that lysosomes are also part of the endomembrane system although their main function is to break down large biomolecules like the carbohydrates lipids proteins nucleic acids even old organelles or even whole cells as we've talked about when we were talking about apoptosis these can also break down or be involved in breaking down pathogens or other things that the cell takes in that needs to be destroyed so let's pretend we have a type of white blood cell this this looks like a parasite almost and this white blood cell is specialized it has greater surface area through these extensions called pseudopods or pseudopodia it's going to take in some food or it could be even a bacterium through the process of endocytosis this is when cells cells take something in into the cell one type of endocytosis is phagocytosis and that means to eat so these are larger particles or larger structures that the cell is taking in it produces a vacuole sometimes we just say vesicle and then this vesicle is going to fuse with the lysosome remember the lysosome is contains digestive enzymes and it's also acidic inside so when they fuse it produces something called a phagol lysosome and let me write that out here phago lysosome so the enzymes from the lysosome will digest the food that was taken in or sometimes it could be a bacterium or other pathogen breakdown occurs and then eventually the particles are going to be released through exocytosis something is leaving the cell and the lysosome is part of the endomembrane system because I can see that part of the vesicle the membrane of that vesicle that initially made up the lysosome is going to fuse with the cell membrane at the end all right and here we are at the end of part three or Arthur video and our fourth and final video we're going to be looking at the cytoskeleton of the cell as well as how animal and plant cells are connected intercellularly between the cells