hello everyone for this lecture we're going to be covering the cell Junctions we have three main General types which are tight junctions anchoring Junctions and GAP Junctions within the anchoring Junctions there are three types desmosomes hemidesmosomes and adherence Junctions before we get started into the different types of cell Junctions I think it's important for us to talk about the different components of the cytoskeleton mainly because I don't cover the cell chapter so the cytoskeleton is going to form this complex thread light Network throughout the cell which is going to consist of three different kinds of protein based filaments which are the microtubules the microfilaments and the intermediate filaments even though both micr ul and microfilaments start with micro which means small a tube is going to be bigger than a filament so the microtubules is going to be the thickest of the three filaments which is going to be made up of this hollow tube that's composed primarily of protein units that's called tubulin these filaments they help Provide support and structure to the cytoplasm of the cell they're also invol involved in cell division and in transport of intracellular materials microtubules also make up two types of cellular appendages that are going to be important for motion which are the cyia and the flagella which we will discuss more on the next slide in contrast with microtubules microfilaments is going to be a thinner type of cytoskeleton filament the primary component of these filament is actin which is a protein that forms these chainlike structures as you can see right over here on the image actin fibers which are twisted chains of actin filaments they're going to constitute a large component of muscle tissue and along with a protein that's called myazin they're going to be responsible for muscle contraction so there's going to be a coupling between the actin filaments and the myosin to promote this muscle contraction besides muscle contraction actin is also going to have this important role during cell division when a cell is about to split in half during the cell division these acting filaments they're going to work also with myazin to create like a cleavage or Groove that eventually will split the cell down the middle and it's going to form two new cells from the original cell the final cytoskeleton filament is going to be the intermediate filament as the name suggest an intermediate filament is a filament intermediate in thickness between the microtubules and the microfilaments these intermediate filaments they're made up of these long fibrous subunits of a protein that's called keratin that are going to bound together like a thread to compose a ropeik structure as you see right over here intermediate filaments together with microtubules they're going to be important for maintaining the cell shape and the structure of the cells unlike the microtubules which are more resistant to compression intermediate filaments they resist tension which are the forces that pull the cells apart so there's all always certain types of tensions that are trying to pull the cells apart and the intermediate filaments are there to hold these cells together therefore they're going to be the main component of cell Junctions which are going to keep these cells together to summarize then we can say that the intermediate filaments are going to be important for cell Junction which is what we're going to cover in this learning outcome and the other two types of cytoskeleton component components which are the microtubules and the microfilaments are going to be important for these plasma membrane extensions which are the Celia the flagellum and the microvilli which we are covering on the next slide I think it's very important for us to cover these plasma membrane extensions because the cyia and the microvilli are going to be an extension of epithelial cells and since this module is covering epithelial cells I think it's important for us to touch on these terms and structures so that you know exactly where they are coming from from the previous slide we already know what microtubules are and microfilaments microtubules form by tubulin microfilament formed by actin filaments so as you can see here two structures the Celia and the flagellum are going to be formed by microtubules and microfil are going to be formed by microfilaments the cyia are going to be found on many body cells including epithelial cells that are going to align the Airways of the respiratory system we can see right over here how they are presented Celia basically means hair so the Celia they're going to move or we say that they're going to beat rhythmically in a way that they're constantly moving waste materials such as dust or mucus or even bacteria that might enter your Airways and they do this to try to get these materials away from the lungs and towards the mouth as you can imagine if bacteria gets into the lungs it's going to give you an infection of your lungs which is mostly called pneumonia so you want to make sure that these cyia are beating in a way that they're trying to take away the foreign objects from your lungs another example of Celia are the Celia that beat on cells in the female Fallopian tubes to move the egg cells from the ovary towards the Urus where they will be fertilized next we have the flagellum the flagellum is going to be an appendage that's going to be way larger than the celium and we can see it right over here compared to the Celia which are shorter and they're going to be specialized for cell Locomotion the only flagellated cells in humans are the sperm cells that must Propel themselves towards the female egg to fertilize it and we can see right over here on this image all the sperms with their long tail or long long flagellum right over there so again the flagellum and the Celia are made up of microtubules and now we're going to talk about the micro which is made up of microfilaments so micro means small Villi or extensions and the microvilli they going to be present mainly in areas where we want to have more absorption or more secretion so it's going to increase the surface area as you can see by having these membrane extensions right over here you're going to be increasing the surface area and therefore you're going to increase what can be absorbed and what can be secreted now that we have covered cytoskeleton components which are the microtubules microfilaments and intermediate filaments and the plasma membrane extensions which are the Celia the flagellum and the microvilli I think it's going to be a little bit easier for you to understand how cell Junctions work in a way to keep the cells together like I said cell Junctions are these structures that will for most part keep the epithelial cells together they do that in a way that there is actually little or no space in between the epithelial cells meaning that the cells of the epithelia are closely connected they're not going to be separated by in cellular material there are three basic types of connections that allow varying degrees of interaction between the cells the tight junctions the anchoring Junctions and the Gap Junctions at one end of the spectrum we have the tight junctions you can see on this image where they're going to be located within adjacent cells these tight junctions they will separate the cells into what we call an apical portion which is the top portion and a basil portion which is the bottom portion because they really squeeze the membranes from adjacent cells in other words when the two adjacent epithelial cells form a tight Junction there is no extracellular space between them and there is no movement of substances through this extracellular space so this is why we can say that the tight Junction separates the cells into what we we call an apical portion which is a top portion and a basil portion which is the bottom portion this allows the epithelia to act as this selective barrier preventing anything from traveling from one cell to the other now these type Junctions they're formed by these webike strands of transmembrane proteins which are proteins that crosses the cell membrane from the external environment into the cell so inside of the cell next we have the anchoring Junctions which include several types of cell Junctions they help to stabilize these epithelial tissues as anchor means to hold in place so anchoring Junctions they're going to be common on the lateral sides of the epithelial tissue and also on the basal part of the epithelial tissues where they are going to provide a strong and flexible connection between the cells there are three types of anchoring Junctions we have what we call the desmosomes the hemidesmosomes and the adherance Junctions the desmosomes are going to contain these patchlike structures which are also called plakes exiting from the plate we're going to have the intermediate filaments which we talked about already which is made of keratin and between the plagues we're going to have the transmembrane glycoproteins that are going to be the ones that will hold the two adjacent membranes together in this case this protein is cin now we go down to the Hemi desmosomes Hemi means half so that's why it's called hemidesmosome because it looks like half of a desmosome these cell Junctions instead of attaching the membrane of adjacent cells it's going to attach the basal part of the membrane of an epithelial cell to the basol lamna while hemidesmosomes are similar in appearance to desmosomes they include the adion Protein that's called integrin instead of having cins like the desmosomes next we have the adherence Junctions these are going to use either cerin or integrin depending on where they are attaching within the epithelial tissue if they're attaching in this case to adjacent plasma membranes you're going to have Catrin as you can see over here in this image that's what they're representing that they're attaching adjacent cell membranes if they were attaching down here to the plasma membrane you would would have an integrin instead of a cine the other difference between the aderan Junctions and the desmosomes is that here we see the presence of actin filament instead of intermediate filament as we talked about actin is also found in muscle cells and they will help with muscle contraction now here on epithelial tissue actin can connect these isolated patches or actually form a beltlike structure as we can see right over here inside the cell and these Junctions they are going to influence the shape and folding of the epithelial tissue in contrast with the tight and anchoring Junctions the Gap Junctions like the name suggests they're going to form this intercellular passageway or a gap between the membranes of adjacent cells to facilitate the move movement of small molecules and ions between the cytoplasm of these adjacent cells these Junctions they are going to allow electrical and metabolic coupling of adjacent cells which coordinates the function in large group cells so because these cells are all closely together with little or no space they're able to coordinate the function of large groups of cells these Gap Junctions they're going to be formed by these structures that are called connexons and what forms the connexons are these proteins that are called connexin for me it makes it easier to remember connections and connections because it's sort of like connecting and that's what Gap Junctions do they connect one cell to another in a way that there can be communication between the cells