Cells

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It's Topic one Cell Structure and Function. So we're going to have a look this week at the cell. And one awesome part of being in science is that you discover beautiful things in science. So you would have noticed on the first slide that there was a banner down the right hand side. And this is the work of David S. Goodsell. He's a structural biologists and an artist, and he pretty much draws these beautiful representations of biological concepts. So this is the cell. And it shows everything that we're going to cover in this part of topic one. So looking at all the various different parts that come together to make a cell so you'll see that very topic, there will be a different sort of picture to illuminate how different it actually looks in reality to How we it looks when we teach, teach it in a deconstructed way. So, as you can see, all of the organelles we're going to talk through in this topic will be, are depicted in this particular drawing so highly recommend going and have a look at his work. It's very, very beautiful.

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So because this is topic one. Let's have a look at learning at university, so we

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use these things called learning outcomes, and you'll see that if you've downloaded the notes from the course site, the first section is learning outcomes. But in the recordings, you'll see that they're often referred to as learning objectives because there's something that you're aiming to do. So each topic has a set of learning outcomes, and once you are working your way through, you should be going back and ticking them off and going - Yes, can I do that? Can I discuss this, or can I describe this or can I list these parts or can I name them? And once you can do that successfully, that means that you've actually understood and retained that knowledge. So when it comes to the quizzes you'll be able to answer all those questions. As those questions are specifically designed to test the learning outcomes. So, for example, here's one from this week - Describe the structure and function (So remember structure is how it's built, function is what it does) of the plasma membrane and explain the various forms of cellular transport. So the example quiz question is Name two molecule types that are embedded in the plasma membrane, which protrude into the extra cellular space, so worth two markss. And that's a sort of an example of a short answer question, but it could be a multiple choice. where you just have to pick the options, and that addresses basically the structure of the plasma membrane. So you can go through as you're working through all these topics and look at all the learning objective and go - What sort of question could be asked about that so that you're testing yourself as you work through the content? So here's all of the learning objectives that we're going to be working our way through in this topic. But the first part is dedicated to the cell, so this will be quite a lot of information, particularly if you haven't done any biology before. It's probably a good idea to watch through once and then move on. Go and have a think about it and then come back to it. If you've never done biology, look at other resources, other textbooks. In order to bring yourself up to speed. To understand all about the cell. So in this part, we're going. To cover learning objectives 1 through to 5 and talk about basically the bits and pieces of all the cells and how they are structured. So how they're built and what function they play in the cell as a unit of life. So we have two different types of cells that exist on planet Earth, and one is simpler and one is complex. So the first one are the prokaryotes. And so these are the old school cell that have been around for a long time. And the key part that distinguishes them is that they don't have a nucleus. They are very, very simple in structure. And generally when we talk about prokaryotes we talk about bacteria and archaea and we'll cover this in a later topic. Now, these were the first forms of life on Earth, and they have been so successful on Earth that they've basically existed for millions of years now. So they're not going to disappear any time soon. And they love to adapt and change to new changes in the environment on earth, the more complex of the cells is the eukaryotes and they have a nucleus. And the reason they have this nucleus is because they do a lot more complicated biochemistry in these cells in order to survive. Now eukaryotes are very, very diverse group of

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organisms, and it starts off with fungi and plants and animals.

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So it's a huge mixed bag of different organisms here on planet Earth that are classed as eukaryotes Now, just as interesting note about the name prokaryote means 'before a nucleus' and eukaryote means 'possess a nucleus' so language can help a lot of people understand sciences So just a note that this actually tells you in the name that one is before the nucleus and one has a nucleus. Now, when we look at how they're depicted generically, this is how they usually present it. So these are generic generalised examples, and as you can see, they sort of have a couple of things in common. But there are some major differences that between those two. Different just by looking at them. Different shape, different features. So we're going to now look at the four differences between the eukaryotic and prokaryotic cells. So the first one is the presence of this membrane-bound nucleus, so that is unique to eukaryotes Prokaryotes just have their DNA floating around in their cytoplams So their, Their DNA is free to move around anywhere in the cell, whereas the eukaryotes built a special room that protects and keeps all of that important genetic information in the one place and protected from the biochemistry that happens elsewhere in the cell. Another thing that you may have noticed from the previous slide is that the eukaryotic cells are much larger than the Prokaryotes cells and that last slide was not to scale. It's a much larger difference because, for example, we can look at ourselves, and if you look at your skin, you can actually see the wrinkles and the creases in between your individual cells. Whereas you can't look at the surface of a desk and go OK, there's a prokaryote on there. There's a bacteria, and that's all salmonella growing along happily on that. On that desk. We need tools in order to be able to see Prokaryotes

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Third one is the presence of these membranes. So Eukaryotes cells have these internal membranes, and basically the first one

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helps protect the nucleus. But then the other ones actually make up all of these organelles that have specific functions in order to allow the cell to live. And because we have all these organelles, we also need to have a structure that supports them. So the eukaryotic cells feature a diverse and dynamic cytoskeleton in order to support not only the complexity of the cell but also the lots of different organelles within it that help it actually live in its environment. So let's have a close up look at the

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Prokaryotes. So, as you can see, this is a bacterial shape. So it's an elongated sort of rod shaped, and it

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has a soup of cytoplasm with everything floating in it. So the ribosomes, which we'll go through it a bit later. Plasmids, which bits of DNA that tell the different Prokaryotes, what they could do and how they can fight disease (smh - fight diseases) fight drugs, for example, and be drug resistant. And then we have these plasma membrane and a cell wall to protect from the outside environment and then last One we have is a flagella, which is a lovely structure that allows movement to occur in

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Prokaryotes So those are the general features that basically, we need to understand that prokaryotes have and will be coming covering more of that when we look at microbiology in a later topic. So how successful have these primitive prokayotes been?

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Well, simple answer is enormously successful because they arose in the primordial soup about 3.5 billion years ago, and they're still here. And so, and they have continued to live in all different sorts of environments that we don't live in. So they can live in the vault, no in the vents of underwater volcanoes. They can live in on rocks and in sulphur rich soils. They can even live where radioactive isotopes have littered the environment, such as where Chernobyl was. And in Japan, where Fukushima had the nuclear meltdown. There are bacteria living quite happily in those conditions, but humans cannot live there now. They are so successful that they can also colonise us. So we are (talking fail, laugh) a collection of both bacterial cells and our own cells. So we have prokaryotes that live on us and in us that allow us to live good and healthy lives Um We have our own cells that allow us to function as humans. And with that, it's often said that the prokaryotes that live on us and is us, outnumber us by like trillions like 30 trillion to 1 and when they are in harmony. So when they're breaking young, our food, when they're protecting our skins from invaders, it's great because we don't notice them. But then, of course, there are always going to be a couple of nefarious ones that will break into our barriers or that we will pick up and put into our body that will then cause us disease. So that's always not a good thing. Now we always have thought and said, throughout textbooks and throughout different sources of knowledge, that the prokaryotes outnumber us in our human body and they've always talked about different ratios. So let's look at that ratio that we just talked

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about. In 1972 the ratio of bacteria that was widely reported by Thomas Lucky was 10 bacterial cells to one human cell, and if that makes you cringe, that's okay. Because, yeah, it's sort of hard to think about the fact that we've got these things in us and on

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us that allow us to live and breathe and process

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things. However, that was in 1972 so that was a while

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ago now, however, in 2016 we learned more, so we learned that that number was incorrect and that when we looked and counted up and did a really, really sensitive experiment to see how much bacteria there is to human

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cells, to the eukaryotic human cells. It was revised too one bacteria to one human cell, and when we put that down to just mass, it's only 200 grams of bacteria in us. But if we were to take away that bacteria from

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us, we wouldn't have a very healthy life. So it's science, and the knowledge that we teach you is always changing. It's always evolving, so some things that you learn today will be true for the next 50 years of your career. But other things will change in the next year or two as we learn more. So good to see and good to appreciate that some things that we learn change whilst we're learning them. So let's get back to our

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Eukaryotes. Let's focus on us for a while, so eukaryotes are what (ride) wide diverse population

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of organisms on the planet. So we have, We could go down to single celled organisms such as algae, amoebam fungi, yeast and they fit in the Eukaryotic group. Then we have more complicated multi-cellular organisms that also fit in the group because they have that same membrane bound nucleus. So plants, animals and we also have, like other animals such as sponges insects, birds, mammals, all of us. All of these organisms have in common the fact that we have a eukaryotic cell which has a membrane bound nucleus. So let's work through now what is involved in these cells? So very simple diagram of what is in here. So we have the cell with this membrane. On the outside, we have our nucleus that has all our genetic information, and then we have a soup that contains everything else. So the cytoplasm is the soup of both the liquid form, which is cytosol and all of the different organelles that exist in the cell. So when that comes all together, they make up the

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cytoplasm. But the cytosol stands alone as just the fluid that fills your cell. So every part of the cell is full, so there is no gaps. There is no air. So let's have a closer look at the at the structures, so we have the plasma membrane that surrounds the cell.

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We then have the soup that contains the cytoskeleton, the organelles, the inclusions and then the cytosol, which is the fluid component. We have a membrane bound nucleus, and we have intracellular material and membrane bound organelles with very specific functions. So those are that covers pretty much everything that's in the cell at a very superficial level.

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So with each of these parts we're going to go through and talk about um, now, one thing to note is that with one or two exceptions, for example, the red blood cells, all of the eukaryotic cells will have this similar set up. The red blood cells. they lose their organelles and they also lose their nucleus

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as they mature. And the main reason is is because their sole function is to transport oxygen and carbon dioxide around the body so they don't need any other organelles because they have one sole function.

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But they still will have a plasma membrane that it would be very, very simplified. For the rest of the cells. It will look like this. It will have embedded proteins, and it will have proteins that sit very close to the surface, and these ones are known as peripheral proteins. The integral ones are the ones that actually breach both sides of the membrane, and they are embedded for both strength and that later on

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We'll learn about ones that have specific functions for transport.

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These green molecules on the outsides are sugars and carbohydrates, and when they connected directly to a lipid molecule here, they called it like a glycolipid. When they're attached to a protein. So this big purple thing here, this big purple thing here they called the glycoprotein. So all of these sugars exist on the outside of

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the cell. On the inside the cell, we've got microfilaments showing the cytoskeleton, which supports the plasma membrane. Because it's big, it provides surface area and it needs to be supported. On the outside, we have an extra cellular matrix, and we'll cover that a bit later in some of the slides.

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So what's the main function of the plasma membrane? Well, it's to control movement of different substances, the main

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one being water. So we need to make sure that that soup on the inside stays soup and doesn't dry out. We also have different molecules such a sodium ions and glucose and proteins. They need to come in and out, dependent on what the cell is actually doing. So. The plasma membrane controls that, and it also communicates. It contains those integral proteins that will act as receptors for signalling molecules to turn things on and off in the cell. So to say - Well, you need to build more of

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this or you need to make more of this hormone

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or you need to replicate. All of that information can be switched on from the outside with specific receptors, and we also have other molecules, which is like the glycoproteins and the glycolipds which allow each cell to attach to another cell in tissues and allows for recognition of self versus alien. Or invader, so it's really important. to have all of these existing on the plasma membrane. Otherwise, we lose important functionalities. Now, when we go over the plasma membrane, you'll find

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that the majority of it is made up of fat. So lipids So fats is the lat term, lipids is the science term So because we have this plasma membrane that's made up

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of lipids, it means that fat soluble molecules can actually move in and out of the cell, and it doesn't need to go through any specific transport in order to get in. So small fat molecules will be able to go basically dissolve directly into a cell if it needs to. Now, with this plasma membrane, it is so important because we wouldn't be ableto control the biochemical reactions in ourselves if we lost control of the movement of these molecules inside and outside of the cell, and we also need to keep them compartmentalised so that they don't affect other parts. So we have differences in concentration between the outside of the cell and the inside of the cell. Now we need to maintain that because if the concentration of molecules in the cell is ever identical or the same to those outside. So to the fluid outside the cell, that cell will die because it's lost control of all of its biochemical reactions. So please note that when we use square brackets, that's to represent concentrations. So we're talking about molarity. You'll know more about that in chemistry.

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So what's the plasma membrane made up of? Well, lipids, and specifically it's a phosphor lipid, bi layer. So we have these beautiful two molecules here with hydro phillic heads on the ends. So that means water loving and these hydrophobic tails that

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extend down into the bottom. And when we have all of these phopholipids come together in a fluid, they automatically arrange themselves in this orientation so you can make your own phospholipid bi layer by putting from oil in a fry pan and

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heating it up and then cool it down. Put a little bit of water in and you'll see that

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shimmer of oil on the top surface. That's a bilayer of lipids and, if you want to disrupt it, put in a drop of soap and watch that layer completely. Dissolve and disappear to the sides. So we have the same sort of function. But we have molecules such as the integral proteins that help keep this phospholipid bilayer together and surrounding ourselves and thereby keeping everything in the cell that needs

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to stay in the cell. So let's have a map of what it consists of, so we have the overarching structure of the cell membrane. It has cholesterol in it that keeps it tough. We have the phosholipids OK with the water loving

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head and the hydraphobic, water hating tail. Ignore sphingolipids For the moment, you'll learn more about those in another course, carbohydrates and proteins coming together. That form the glycoproteins and the glycolipids and working together with the lipid bi layer to create this membrane. Which will do all of these functionalities so being the selective barrier, providing stability, providing cell recognition and providing an immune response, which is needed from time to time. So the main take away message from this is that the plasma membrane has multiple components, each one that you should should know. So you know the cholesterol a fat molecule and that we have a lipid bilayer that supports that. And then we have these glycolipids and proteins and they all come together to be a selective barrier to allow the movements of molecules inside and outside of the cell in a very controlled manner because we want to keep the fluid within the cell. So why is that important? Well, because the viscous region of the cell has all the different components that we need to do our biochemical reactions.

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So we have the cytoplasm. So remember, the cytoplasm is the soup that encompasses all

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of the organelles inclusions and the cytoskeleton in a fluid called the cytosol. So all of that needs to be kept inside the cell. We don't want it to leak out because then we'll lose control of the functions of the cell.

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Now let's have a look at the cytoskeleton. So you can see here. We've got some strands that is helping to support the actual structure of the cell. So when we look at the cytoskeleton, it's all about creating three dimensional space so that the different organelles can move around within the cell when they need to. So we have three different sort of filaments that exist. We have microtubules, which are called tubulin So this one here they're the big fat ones. Then we have micro filaments which called actin, and we

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have intermediate filaments which do a variety of different, different functions. So they're all needed for cell shape as anchoring points for cell division and for movement. So we'll go through these different examples to see how how they actually help and function keep the function of the cell. So the microtubules there large hollow tubes made of tubulin, and they really provide stability in terms of making sure that organelles moved to specific points in the cell, particularly if we're going through cell division. So they provide these tracks throughout the cell. That means that we can move different products from one part of the cell to another, or we can even move an organelle to another part, which is really cool, and that's done in an energy dependent process. Now, with ourselves, with animal eukaryotic cells We have two little starting points called centrioles, which directs the movement off our DNA during cell division. So that's one of the most important roles that microtubules actually does in the eukaryotic cells In other cells, we have it acting as both cilia and flagella So cilia is all about movement and moving liquids past a particular cell. So we have lots of cilia in our throat in order to move mucus. We also have flagella but we only have that in one cell type in humans, and that's the sperm. So we need that to be able to flow towards an egg and basically fertilise an egg for procreation. But flagella is very common in the protissts and also in some prokaryotes Now cilia will beat back and forth in a very rhythmic way in order to move fluids in a uni directional way. Whereas flagella actually rotate like a rotor on a helicopter in order to move the cell in a uni directional manner so in one direction, and be able to manoeuvre around if it needs to. So moving on to the next filament which is

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actin. So you'll learn a lot about actin because it's

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a smaller cytoskeleton elements. And not only does it help keep shape in cells. whilst they are in tissues They also control movement. So it's a very, very important thing - filament within the cytoskeleton. Whoops. So and it's also fundamental in moving our muscles. So the partner of actin is myosin, and basically, when we want to move muscles, we can rely on that partnering in order to have a muscle contraction. Other examples of how actin myosin help in eukaryotic cell functioning is by cytokinesis when we need to separate two daughter cells during cell division or in plants when we want cytoplasmic streaming. So when we want the movement of the cytosol throughout the plant cell. So in order to move things around and move molecules. So in this example we've got amoeboid movement where we have an amoeba extending itself in order to move towards food and on the bottom, we have cytoplasmic streaming of the cytosol. So in order to move it around and get those molecules moving to where they need to go in the cell. Now, these are just two examples, and there's videos attached so you can have a look at it down the microscope see what it looks like.

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The final. The final filament that we're going to look at is the intermediate filaments, and they're very, very, very cool because they're all about providing strength. So the intermediate filaments is about holding the shape

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of the cell and putting the nucleus in its place so it stays in a centrally located position. Later on, we will see another example of intermediate filaments when they're working at the tissue level, so we will look a the intermediate filaments a bit later on. But you don't need to know all of these in detail. So we've talked about keeping things in place and keeping the nuclear separate, because all of these different parts of the cell all have very specialist jobs in order to keep the cell alive. So the nucleus is centrally located, and it's a compartment for our genetic information, which is the instruction manual for how to be yourself and how to be a eukaryotic cell.

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So we need to protect that, and that's why it's

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in that organelle But we also have other organelles that build things for

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us and allow us tp keep existing and growing

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and ageing, so that compartmentalisation allows each of these reactions to occur separately from the rest of the cellular machinery and the rest of the cytoplasm and allows specific transport of products to specific parts of the cell. So whether that be into storage so that we can have a molecule available later on during times of starvation,

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for example, or to released a product into the body to circulate. We also have other products such as digestive enzymes that we don't want to be able to to release into the cell because that means that we would digest ourselves. So we need as eukaryotic complex cells to keep all

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of these reactions safe and keep them away from each other so that the cell can keep functioning in a really healthy way.

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So let's start off and look at each of the organelles, So the first one and the most famous one

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is the nucleus. It's made up of the nuclear envelope. It has a nucleolus, and it has chromosomes in it, and that all three of those come together to form the nucleus. Anytime you see a pink square, it's a term that you should know, be able to spell and be able to define. So structure first, we have a double membrane nuclear envelope now, of course, because we want things to be able to move in and out of the nucleus in a very controlled manner. We also have these beautiful nuclear pores that allow movement of RNA and proteins in and out of the nucleus. So what are the functions? Functions are to house the instruction manual for being a cell Which is the genetic material. The nucleolus has a slightly different function because it has to make ribosomal RNA and ribosomal sub units in order to make proteins. But we'll discuss that in a couple of slides. So when we look up close and personal at the nucleus using electron microscopy, we can see that these they've got this very thick, pore - sorry, very thick membrane. But it's filled with these pore complexes that allow the movement outside and into the nucleus of these ribosomal parts.

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So it's very thick. It's very, very strong in order to maintain that instruction manual, because without it we would lose the ability to for the cell to function. So the nucleus is at the centre. The next one that we're going to talk about is this thing that's attached to the nucleus.

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This thing here in the blue with the folds and that's known as the endoplasmic reticulum Now, the endoplasmic reticulum has two portions.

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Okay, so two subsets. The rough endoplasmic reticulum and the smooth endoplasmic reticulum. So we'll cover both now. So the rough endoplasmic reticulum has ribosomes fixed to the outside of this membrane. Now, this is a network of folded membrane that makes these pockets and these sacks, in order to make proteins.

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So the function is to make proteins and to either ship them or keep them there to be processed in the rough ER lumen. So we have a very specific function for the rough endoplasmic reticulum, making proteins using these fixed ribosomes on the outside of the surface. And when we look at the structure closer using electron, microscopy and you can see the roughness, you can see the ribosomes on the outside off the ER, and they're all making proteins. And you'll also have free ribosomes existing in the cytoplasm, making proteins as well, just in a different spot. So let's have a quick look at the protein factories. So these ribosomes, they're not traditionally thought of as an organelle because they're non-membranous It doesn't have a plasma membrane. They're actually a little molecular machine. Okay, and it has two parts: a large and a small subunit that contains RNA molecules that end up producing proteins. Now, ribosomes, depending on what protein they're making, can be attached. to the rough endoplasmic reticulum or

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they can exist free in the cytosol, floating in

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the fluid part of the cytoplasm. So with these little factories, they are always going to exist to just make protein. That's their only function, never changes. So when they're attached to the rough ER, they're making proteins to exist in that lumen space. What about the smooth one?

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Well, it's just a descriptive name because it looks smooth. It's still membrane, and it, because it doesn't have the ribosomes it looks nice and smooth, so that's why it ended up with the name Smooth again. It's continuous with the rough ER So it's still sharing pockets with the endoplasmic reticulum that's rough and also connected up to the nucleus. However, the function of the smooth is to produce a different molecule type. So it's all about the lipids, so the fat molecules and also cholesterol, so the main functions is to absorb

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and transport lipids and make them, from particularly if they're in the cells that line the gastrointestinal tract. And they also build enzymes to detoxify but lipid based substances such as pesticides and final, which will become more apparent why this is an important function, but they're also a reservoir for calcium irons, so the smooth endoplasmic reticulum is everything else but proteins, so lipids, cholesterol, calcium and some enzymes. So when we look at it, it looks a bit more tubular because it doesn't have to ayer itself like the rough endoplasmic reticulum. And we've just got all of this smooth membrane folding in on itself into a sort of tubular network. The next important organelle is the golgi apparatus, so this is this membrane sac over here and over here demonstrated in blue. Now the structure is this, flat pancake like membranous sacs that pinch off at the edges. So here and here. Now, the reason why we have

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these little pinched off vesicles is because the Golgi apparatus sort of functions like the Australia Post of Australia. It sends molecules where they need to go. So it basically anything that's made in the ER, whether or not it's a protein or a lipid, get sent to the Golgi apparatus. The Golgi apparatus will then modify, concentrate, and then package it up. So and then make sure that when they're packaged, they're going to the right destination.

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So they have the address and the instructions all put there ready to go so that they go in the right spots.

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So the Golgi really, really important for cellular functioning Next up is the mitochondria. So this is the powerhouse. So it makes the energy for the cell. Now really cool thing That about the mitochondria is that it has prakaryotic origins, which we'll talk about a bit later. So at some point, billions and billions of years ago, a eukaryotic cell met a prokaryotic cell and said, Hey, do you wanna make some molecules for us and I will offer you a nice warm home and protect you from the various prey that wants to eat you.

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And they formed this partnership where the prokaryote, knowing how to burn oxygen to make ATP all of a sudden, made this cell able to function at a higher level. So the mitochondria, which is a plural; mitochondrion is single, allows the cell to exist in terms of energy by providing aerobic respiration, which is making ATP with

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oxygen. So the structure of the mitochodira, it looks very similar to a a prokaryote Sorry. So it has two membranes and the inner one is folded,

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in upon itself. And the sac like cristae are where reactions happen. So how we know that this mitochondria used to exist separately to us is that it has its own DNA, and it manufactures some of some of its own ribosomes. So it is can exist separately from the other organelles. Not that at this point in time, it could choose to abandon us as eukaryotes. The relationship is well established because of one function it does of making ATP is the core function and we would not be able to exist without the.... Without that molecule, we wouldn't be able to do probably 75% of the reactions that are happening now in ourselves without it. So how did it all start? Well, it was probably ingested and it survived. And went - You know what this particular cell is providing me with a good home, I'm protected. I've got a stable environment. I'm going to stay here. And this ability to burn sugar so glucose and make 38 molecules of ATP which is energy rich molecule, changed the way the cell works because previously that in order to make ATP, you had to do without oxygen and we could only make 2 ATP molecules at a time in the absence of oxygen. So by getting this amazing prokaryote to come into the cell and provide that that energy allowed us to basically change and adapt to the environments and build multi-cellular organisms like us that can actually live and exist in our ever changing environments. So the mitochondria is here to stay, and we

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are very grateful that it came. Next up lysosomes. So as we age, things start to break down and

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organelles will start to not work correctly or you might even have an invasion of bacteria. And we need a demolition crew in order to remove those unwanted parts from ourselves in order to keep the cell healthy. And we also can get rid of entire unwanted cells in the body. So I thing called apoptosis when we want or otherwise known as cell suicide, when we need a cell to die because it's no longer functioning properly. So lysosomes are a single membrane bound structure containing about 40 different digestive enzymes. So it's very, very important that it doesn't burst because if it bursts, it will digest or denature almost any biological macromolecule because they can dispose of pretty much anything that's biological in nature, such as bacteria, cell membranes, nucleus, DNA, everything, so we don't want that to

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happen, so the lysosome needs to be kept separately and kept very well, so if they do burst, we then have the problems

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of digesting ourselves, and that term is called autolysis auto meaning us, lysis meaning destruction. So there's multiple ways that lysosomes could be used in the body. Sorry. in the cells so we can have them combining with the food vacuole So, for example, when we've had a cell decide there's some food I need to digest that. Let's bring it into the cell. So we will then have the digestive enzymes fuse of that, and we will break down the food particles. Now when we have a misfiring cell, organelle Sorry, we will actually try and dissolve it ourselves. So we will have a vesicle that will isolate and sequester that damaged organelle and the lysosome will come along and fuse again and then break down that organelle. now that organelles pieces won't be wasted, they'll be reused to build other things in the cell that need to replace that that mitochondria, for example. We also have one other sort of digestive organelle which is the peroxisomes and again single membrane sequestered away from everything else because it's all about enzymes to degrade harmful substances. So this peroxisomes is not about disposing of the old or not working organelles. It's more about keeping a track of any by-products or metabolites that are made. That can cause cellular issues such as free radicals, hydrogen peroxide, those sorts of things that need to be neutralised in order for the cell to stay healthy. So it's all about neutralisation of chemicals that can cause chain reactions. Last part is the cytoplasm and their inclusions, so the inclusions are not membrane bound organelles, but they're usually macro molecules for storage of substances. So, for example, glycogen is all about storing sugars. Lipid is all about storing fats, so we want to save them for a later time or times of starvation. So we put these things away as inclusion bodies. And, of course, we will also have things such as enzymes or cellular protein in order to just maintain the cell in terms of its concentration of molecules that it needs to continue to to move with. So the last one, which is on the outside, is the extra cellular matrix, So these are the molecules on the outside. It's usually unstructured sorry, structured, well-filled with a ground substance, which is a liquid material that fills the spaces between cells. So in the extra cellular matrix, we have adhesion molecules such as lamellin that connect to the neighbouring cells. We also have the proteoglycans. So proteo meaning protein, glycans, I mean proteo means proteins, glycans means sugars in order to identify and help the cell be identified and connect to the neighbour next door. So that's everything from the nucleus. So in the dead centre of the cell, all the way out to the outside of the plasma membrane. Now, one thing that we need to touch upon is the fact that all of these organelles, whilst we've looked at them individually, they all come together to actually transport things around the cell, and this is known as the Endo Membrane transport system. So it's all about moving molecules and trafficking them to where they need to be. So, for example, when we make a protein that needs to go outside the cell, the whole process starts from the very beginning in the nucleus and then moves through the E. R to the Golgi and so on and so forth until it ends up where it needs to be. So we need to be able be aware that all of these individual organelles work together to make sure the products that they make such as proteins gets shipped through safely to its final destination without any uncontrolled modifications. So we start off in the nucleus where we have messenger RNA, which holds the code for proteins. So we need to get that information out of the nucleus and then into where it needs to be dealt with. So it all begins in the nucleus. Now the next diagram pretty much shows thie entire network. So we start off in the nucleus where we get our information. It then needs to move out into the rough. ER. So let's say It's going to be a protein. So it gets that information, that instruction of how to make that protein gets moved to the rough E. R. It then makes that protein, and then it shifts it and puts it in a vesicle to send it to the Golgi apparatus. The Golgi apparatus then deals with it. It will make changes if it needs to. It will modify it as needs be, and then it will package it off for shipping to its final different destination. Now, if it gets it and goes - this is wrong. Something is wrong here. This doesn't work properly. I need to destroy it. Then it will basically cause it to fuse with lysosome to digest it and allow those components to be reused again. Now, of course, once we have successful packaging and go Yep, this is 100% right It needs to go to the next destination. It will then fuse with the plasma membrane and allow that protein to be secreted from the cell. So this is the entire Endo membrane transport system involving all of the aforementioned organelles. So very, very important. And with that transport, because we have so many organelles involved, we need to make sure it's supported and that things are moved from one point to the next. So the cytoskeleton helps with during that. So it is constantly changing and moving to allow that endo membrane transport system to occur and to allow those proteins to be moved from one place to the other. So that's the end of part one, so please refer to your textbook for sections 3.1 to point two and 3.7 - 3 point eight of Chapter 3 cells. The living units. Thank you for listening.