Understanding Cell Structure and Functions

In this section of microbiology, we are looking at cells. We're going to look at the anatomy of both prokaryotic cells and eukaryotic cells because we have microorganisms that are prokaryotic and we also have microorganisms that are eukaryotic. So some of this might be information that we already know, like what's the difference between a prokaryotic cell and a eukaryotic cell. and some of the organelles that are found in eukaryotic cells and their functions. And then some of it is going to be new information about bacterial cells that we'll be using until the end of the semester. So first, let's look at the differences between prokaryotic cells and eukaryotic cells. So eukaryotic cells, let's look at that first. The chromosomes in eukaryotic cells are paired chromosomes. They are found in the nucleus. which is one of the organelles eukaryotic cells have organelles inside of them and eukaryotic cells divide by mitosis so from previous biology courses you have probably learned about mitosis which is basically how cells divide and double and so on now the prokaryotic cells actually have one circular chromosome so For example, eukaryotic chromosomes, they kind of look like this if you've ever seen them, right? They're paired chromosomes. Whereas prokaryotic chromosomes, it's like one circular chromosome, so it looks pretty different. So whenever we look at bacterial chromosomes, we're going to notice that it has a circular DNA because remember bacteria are prokaryotes. Prokaryotic cells also are prokaryotes. do not have organelles so their genetic material is not in the nucleus there's no nucleus it's just somewhere inside the cell also bacteria have cell walls made up of peptidoglycan which we've learned before and they divide by binary fission which is budding so one cell will slip into two cells and that's how they move on from one generation to the next generation and so on So we're going to first look at prokaryotic cells, specifically bacteria. So first let's discuss bacterial cells size. So the average size of a bacterial cell is 0.2 to 2.0 micrometers. Okay, so it's really, really, really small. And so we're going to look at that, and obviously we started looking at bacteria with the microscope, and we know that they're really, really, really tiny. Most bacteria are considered to be monomorphic, meaning they are just one single shape. So, for example, all the bacterial cells of Staphylococcus aureus are all going to be circular in shape, or all bacterial cells of E. coli are going to be elongated. So usually they're just one single shape. So now we have to learn the vocabulary of what these shapes are. So this is really, really important. And this is something we carry on throughout the whole semester. So if bacterial cells are rod shapes, they kind of look long like a rod. We call that bacillus. So the shape is bacillus. That's the correct term. If it's spherical or round or circular shaped, we call that caucus. Now some bacterial cells are actually kind of spiral or they kind of are like wiggly. We can call them vibrio or spirochetes. So spirochetes, that shape is like a coiled shape, kind of like a corkscrew shape. And vibrio is a comma shape, so it kind of looks like a curved rod. So if you look here, here's vibrio and then here's a spirochete, which we'll talk about. It'll come up again this semester. Now the arrangement is also important when we're looking at bacterial cells. So if bacterial cells are in pairs, so they're just like two together, we call that diplo. In clusters, we say staphylo. If they're in chains, we say strepto. And if they're in four groups of fours, we call that tetra. Depending on the shape and the arrangement, we would call it one of these words. So for example, if I have pairs of rod-shaped cells, I would call it diplobacilli. If I have chains of circular spherical cells, I would call it streptococci. So this is what that looks like. So here you could see that they're in pairs, right, and then it's circular in shape. Tetrad is four of them. Remember, staphylo is just a group of them, like a cluster of them all together. And same thing applies for bacillus. So here are those bacillus shaped cells that are elongated. Now there are some species of bacteria that their rods are so tiny that they kind of look like spheres. And so that's one that we have to be careful of because that one is really hard to tell when we look through the microscope. Here again diplobacilli. So here we have pairs of them and then here are chains of them. Okay so sometimes it's going to give you information about the shape of or it's going to give you information about what that cell is going to look like. So for example staphylococcus we know that Those cells are going to be spherical. We also have a genus called Bacillus. The Bacillus genus, what shape do we think that all of the cells have? They're going to have a Bacillus shape. So there's one called Bacillus anthracis. That's the bacterium that causes anthrax, if you've ever heard of anthrax before. And you can see that it's chains of these Bacillus shaped or rod shaped cells. So Any species under the bacillus genus is going to be bacillus shaped. So that was just an example. Okay, now let's look at structures that are outside of the cell wall, kind of exterior structures of bacterial cells. One of them is called the glycocalyx. When you see glyco, think of carbohydrates. So glycocalyx is like this layer of polysaccharide, but it could also be... made of protein but most of the time it's made up of carbohydrates it's outside of the cell wall kind of like an extra layer external to the cell wall and it has this like jelly-like consistency this thick viscous consistency and there are two examples of a glycocalyx a capsule and the slime layer so a capsule we call it a capsule if it's really organized and it's really um it's bound very tightly to the cell wall and if it's kind of loose and undisorganized we call it a slime layer so here you can see an example so this is of streptococcus pneumoniae and you can see that you have the cells and then you have the outside and then here in like this aqua this aqua layer right here that would be a capsule okay flagella some bacteria are motile, so they have motility. So they may have flagella that helps them travel and move. So flagella is really, really advantageous to bacteria. Again, it's an external structure kind of sticking out of the cell, and it helps propel bacteria to a favorable environment. So if a bacteria likes to move toward an environment that they like or away from an environment that's not favorable, that they don't like, this is called taxis and flagella are able to provide bacteria the taxis to move towards things that they like and away from things that they don't like. So this is like a really detailed image of what a flagellum consists of. So flagellum is singular, flagella is plural. So here you can see there's some flagella kind of sticking out of the cell wall of the bacteria. and you can see how complex the structure is and it uses atp because it has to be able to move okay now flagella can be arranged differently so there are different arrangements of flagella for example if the flagella is all over the bacterial cells like it's all around kind of like it's all covered in hair we call that peritrichous arrangement if it's just at the ends of the bacterial cell we would call it amphitrichous or we would call it polar flagella. Now sometimes a bacterial cell just has one single flagella, sometimes they have like ten flagella but it's still just on one end, so there's different arrangements of bacterial flagella. Now another structure that kind of Looks like flagella in the beginning, but it's not. This is called axial filaments. Axial filaments are located only in spirochete cells. So if you recall, spirochete cells, they had that coiled like corkscrew structure, kind of that spiral look to them. Axial filaments are kind of like an extension, kind of sticking out of the cell. However, they kind of circle back around the cell and they kind of twist it. So think of you. twisting a strand of hair and kind of turning it into like this corkscrew or coil-like structure. That's what the axial filament does. It kind of circles back on the cell, wraps around the cell, and causes it to have this coiled-like appearance, which is really, really helpful to the bacteria because it helps the bacteria navigate and go through areas that are super viscous, super thick. That shape, that corkscrew shape, helps it survive in those areas. so this is what it looks like so here's that axial filament it wraps back around the spirochete causing it to have that spiral shape okay there are also these um structures called fimbriae and pili fimbriae are these hair-like structures and they're really important for attachment pili are also used for attachment but they're also involved in motility So this is what fimbriae looks like. So you can see these kind of like hair-like structures sticking out. And it's important if this bacterial cell finds an environment that it really likes, or in other words, a favorable environment, they can attach to whatever that surface is. So pili, we're going to look at a little bit more later on, but they are both for attachment and for motility. Okay, what about the cell... wall. The cell wall of bacteria is very, very, very protective. Not only does it protect the cell membrane of the bacterial cell, it also prevents osmotic lysis. This is when too much water fills up in a cell and it causes the cell to kind of blow up, blow up, blow up, and swell so much that it can burst and basically die. Now, if you recall, the cell wall of bacterial cells is made up of peptidoglycan. So now we're going to go into detail as to what peptidoglycan is. What is that? So peptid, peptide, what do you think of when you see this? You think of protein. Glyco or glycan, you think of carbohydrates. And that's what peptidoglycan is. It's this really complex compound that's made up of proteins and carbohydrates. So first, let's talk about the carbohydrates. So there are these repeating disaccharides in these rows called NAG and NAM. So NAG stands for N-acetylglucosamine. NAM stands for N-acetylmuramic acid. You don't have to know the full word, but you should know NAG and NAM. So it's kind of like a pattern of repeating units. So it's like NAG, NAM, NAG, NAM, NAG, NAM. It's like one and then the other. Kind of these repeating, and there's like these rows of these. carbohydrates and the rows of the carbohydrates are linked together they're connected to each other by protein bridges or in other words polypeptides so sorry i moved my screen okay so here we have the nag and the nam so here's the nag nam and so it would be nag nam nag nam and so on you have these kind of like these chains of carbohydrates so this is what it looks like so nagnam nagnam all the way through and you have these chains of them these rows of carbohydrates and here between the carbohydrates you have peptide bridges protein bridges basically linking them together and it kind of makes like this cage-like appearance and that's literally what this cell wall is that surrounds the outside of the cell membrane now when we're thinking about the cell wall of bacteria It brings us to two categories of bacteria. Some bacteria are known as gram-positive bacteria, and some bacteria are known as gram-negative bacteria. So what does this mean? This has to do with the cell wall of the bacteria. So it's these two big categories of gram-positive or gram-negative. So gram-positive cell walls have a very thick peptidoglycan. They have many, many multiple layers of this peptidoglycan, whereas gram-negative cell walls have just one single layer of peptidoglycan, so they have thinner cell walls. However, gram-negative cells also have an extra cell membrane. So not only do they have the cell membrane, the typical cell membrane of the bacterial cell, then they have one layer of peptidoglycan, and then they have an outer membrane surrounding it. So the space between the inner or typical cell membrane and the outer membrane is known as the periplasmic space or the periplasm. So let's take a look here. Here, just by looking at it, I would already see that this is a gram positive bacterial cell wall because I have multiple layers of peptidoglycan. Another thing I would notice is that there's no outer membrane, right? That's only specific to gram negative. Looking at this image right here, I could tell that it's a gram. negative bacterial cell because I have the cell membrane. I have one single layer of peptidoglycan and then I have that outer membrane here. Now something really important that we have to know about the outer membrane of gram negative bacteria is that there's something in there called lipopolysaccharides. So these blue structures that are embedded in that outer membrane are called lipopolysaccharides. called lipopolysaccharide LPS so lipo refers to lipids polysaccharide of course it's a carbohydrate so this is made up of a type of polysaccharide and a type of lipid so the polysaccharide is called a polysaccharide the lipid is called lipid a I want you to remember LPS is toxic it's considered what we call an endotoxin, which we'll revisit later on in a later chapter this semester, but LPS is very toxic. So if, for example, oh, and before I say my example, the toxic part of LPS is the lipid A, that's the part that's toxic. So if, for example, I have an infection by a gram-negative bacteria, so the bacteria that's infecting me is gram-negative. If you use a certain antibiotic to basically kill the bacterial cell and that antibiotic causes this outer membrane of the bacterial cell to basically break up or burst That means that LPS gets released and that's really dangerous because LPS is toxic to us So it would end up causing septic shock and a bunch of other things in the body. So it's really it could be fatal Okay, so how can I find out if I'm working with a bacterium in lab and I want to find out is this bacterium a gram-positive or a gram-negative bacterium? So we do gram staining. You might hear my dog bark sometimes. So what you do to figure out if it's gram-positive or negative, you do... gram staining. So it's a staining method. We don't have to learn the details of this. The details of this we'll learn when we're in lab. But after you do the gram staining on the bacteria, if your bacterial cells end up being stained purple, they're gram positive. If they end up being stained red or pink, they're gram negative. So if you look at a gram stain, and after the gram staining method, you look at your microscope slide, if it's purple, it's gram positive if it's pink or red it is gram negative okay so there are also cell walls that are different and unique so we call these atypical cell walls and one of the main examples of a unique or atypical cell walls are acid fast cell walls acid fast bacteria have a unique cell wall because they have this waxy lipid called mycolic acid bound to the peptidoglycan. So they basically have mycolic acid, this specific compound, this specific lipid inside of their cell wall that makes them different. It's really helpful and advantageous for them. We'll revisit this later on. But a type of bacterium, genus of bacteria that has acid-fast cell walls are mycobacterium. So if you've ever heard of... Mycobacterium tuberculosis, it causes tuberculosis. This one is considered an acid-fast bacteria. So it's not positive or negative, it's a different category. Now for this one, you can't really do gram staining on it, so you do another staining method in lab called acid-fast staining. So this is another one that the steps of this we'll learn in lab, but this is what it looks like. If I want to figure out if, let's say I want to figure out if mycobacterium tuberculosis is acid fast or not acid fast, I would do this whole staining method. And if I end up getting cells that are stained like this fuchsia hot pink color, that's positive. That means yes, it is acid fast. If I end up getting blue, then it would be not acid fast. Our next example of having an atypical cell wall. are the mycoplasmas. This genus of bacteria don't even have a cell wall. They lack cell walls. That's because they have undergone something called reductive evolution, okay? And reductive evolution or degenerative evolution, this is when it's kind of like if you don't use it, you lose it. They've lost the need to have a cell wall because they live inside the host, so they're already kind of protected. And so they've evolved to not even have a cell wall anymore. So pretty interesting. Now, there are also structures we have to talk about that are inside the cell wall, inside of the cell. So obviously, there's the plasma membrane. The plasma membrane is very, very protective. It has a lot of functions. And we've learned that it's made up of a phospholipid bilayer, or in other words, two layers of phospholipids, right? and that's the main component of the plasma membrane or the cell membrane. But there are also proteins that are embedded inside of that cell membrane, and they're very, very helpful in the functioning of the cell membrane. Now, there are two types of proteins. There are proteins called peripheral proteins that they only stay on one layer, like one side of the cell membrane. And then we also have integral or transmembrane proteins that penetrate the membrane and they basically are embedded really deeply and on both sides of that bilayer. So here is my phospholipid bilayer of my cell membrane, and I have peripheral proteins just on one side of the layers, and then I can have integral proteins or transmembrane proteins kind of spanning that entire plasma membrane. Now there's something called the fluid mosaic model. The fluid mosaic model basically tells us that it's not just phospholipids that make up the cell membrane right there are proteins in there and it's also fluid so there's movement there phospholipids can rotate they can move laterally proteins can move from one spot to another spot and the membrane is lipid-like another cool thing about the plasma membrane is that it is self-sealing so if it opens up it'll seal right back up so it's fluid. So we call that the fluid mosaic model. So what are the functions of the plasma membrane? A really important function or quality of the plasma membrane is selective permeability. Selective permeability basically describes the plasma membrane's function of allowing some molecules to go through and not others. So it is selective in what can enter and or exit a cell. And so how do molecules actually enter and exit the cells? So there are two kind of big general categories. These are called passive processes and active processes. Now in a passive process, just think of it, it's passive, it's just relaxed, it does not require any energy. This is when substances move from an area of health. high concentration to an area of low concentration. And whenever you hear the word concentration, think of level or amount. So for example, if I have salt and it wants to move, well, let me use another analogy. So let's say we are in a classroom, okay? We're in a classroom and we have 50 students in our classroom, but I have a classroom next door. that's only three students in there or five students in there, let's say. What would I ask you to do? What was like the first thing I would think to do? I would think to kind of split up the class, right? I would ask some of us to move to the other classroom. So we went from an area of high concentration of students to an area of low concentration of students, okay? That's a passive process. An active process would be the opposite. So this is when substances move from low concentration area to a high concentration area. And in order to do this, this is kind of like against the natural flow of things. And so since you're going against that natural flow, you need energy. So active processes, they're called active because they require energy. So that would be instead of the first thing that would come to mind is, hey, let's even out the classes. If let's say I told those five students to enter our class and now I have even more students. That's going from an area of high of high sorry that's going from an area of low concentration to an area of high concentration so you're going against that natural flow of things which is why atp energy is required for active processes so we're first going to talk about passive processes because there are a few different types of passive processes one example of a passive process is called simple diffusion Simple diffusion is basically what I described when I was describing a passive process. So it's a movement of a solute from an area of high concentration to an area of low concentration. And this is to reach something called equilibrium. So this is to reach basically balancing out. So when we're talking about the inside of the cell versus the outside of the cell, let's say the inside has a lot of salt and the outside doesn't. In simple diffusion, the salt will basically diffuse outside of the cell until the inside and the outside are equaled out or balanced out and that's equilibrium that's simple diffusion and it's a passive process so it does not require any energy so let's say in this example this is the lipid bilayer or in other words the cell membrane right here's outside of the cell and here's inside of the cell we have a lot more on the outside compared to the inside. So what will simple diffusion do? Going from high concentration to a low concentration. So in this case, molecules or solutes will travel inside. We call this going down the concentration gradient. Anytime you have a difference in concentration outside versus inside of a cell. it creates a gradient. In this case, it's a concentration gradient. That means there's an unequalness going on here. And so if I say that solutes are traveling down their concentration gradient, this is what I mean, going from high concentration to low concentration. Now there's another type of diffusion called facilitated diffusion. Facilitated diffusion is the same thing, except the solutes need a little bit of help. So they'll usually combine with a transporter protein. They basically need someone to kind of carry them through the cell membrane. This is if the molecule is a larger molecule, it's going to have a harder time passing through. If the molecule is charged, like a charged ion, that's going to be harder to go through with that concentration gradient. So here's an example of that. So here's the bilayer and here's a protein, like an integral protein or transmembrane protein. And it serves as either like a channel or a carrier. So we're still moving down the concentration gradient, but we just need a little bit of help going through. But still, no energy is used. So there's some facilitation going on. So it's facilitated diffusion. Okay, another type of passive process is osmosis. Now, when you think of osmosis, think of the movement of water. So the movement of water across that selectively permeable cell membrane from an area of high water to an area of lower water concentration. Now, water does this a little differently. There are these tiny little water channels. They're literally like little holes for water. And we call those aquaporins. Aquaporins basically like water pour. Okay, so aquaporins are all over the cell membrane. and water can go through it to either enter the cell or exit the cell either direction and this is by osmosis again another type of passive process so no energy is needed but water is also going to want to balance out so it's going to want to balance out like the ratio between water and solute or in other words the ratio between solvent and solute so if i have a lot of salt on one side water is going to follow wherever you have too much salt to kind of balance out that water salt ratio. Now I want you to keep one thing in mind and write it down if you need to. Water always follows salt and I'm using salt as an example here but it's any type of solute. It could be sugar, it could be anything else. Water always follows salt so wherever there's a lot of salt or a lot of solute, water is going to go there okay to kind of balance that out. So there's also something called osmotic pressure, and that's the pressure that's needed to stop the movement of water across the membrane. So depending on where I have a lot of solute and where I have a lot of water, that's going to determine the movement of osmosis so once again water follows salt so depending on where i have a lot of solute that's the direction water is going to go that's going to determine hey is water going to enter the cell or is water going to exit the cell so there are three situations that can happen three different types of solutions so if this is a cell right here So this little baggie, it serves as a cell. And then here's the solution that surrounds it. So you have like a beaker of solution and the cell is inside of it. Depending on if there's a lot of solute in that solution or a little bit of solute, that's going to determine the movement of water. So three types of solutions that we have to look at. We have isotonic, hypotonic, and hypertonic. So let's first talk about hypertonic solutions. means what? Hyper means a lot, right? Or really high or a lot, like a big amount. So in a hypertonic solution, I have a really high solute concentration compared to inside of the cell. Or in other words, in a hypertonic solution, there's a lot more solute in the solution compared to inside of the cell. So what direction is water going to move? So if my cell is in a hypertonic solution where there's a lot more salt in the solution compared to inside of the cell, water is going to move out of the cell. Remember, it's going to follow wherever there's more solute. So water will leave the cell. And what happens if a bunch of water leaves the cell? The cell kind of shrinks and shrivels up. And then the opposite is true. In a hypotonic solution, hypo means low or below. So a hypotonic solution has way less solute or lower solute concentration compared to the inside of the cell. So where is water going to go? Water is going to go where there's more solute. In this case, there's relatively more solute inside of the cell. So when a cell is placed in a hypotonic solution, water enters the cell. Water moves into the cell. And so what would happen to the cell if water keeps entering it? It's going to swell up so much that it can possibly burst, or in other words, lyse. So what if there's an isotonic solution? Iso means same. So in an isotonic solution, the solute concentration outside is equal to the solute concentration inside. So then what does water do in that case when one is not higher than the other? You might think at first, it's natural to first think that, okay, then water doesn't move anywhere. It doesn't move out and it doesn't move in because it doesn't need to. However, keep in mind that water is always moving in and out of the cell. Water doesn't just stop doing it. So actually, the rate or the amount of water entering the cell is balanced with or equal to water exiting the cell. So the water is at equilibrium. So it's not that it's not moving at all. It's just moving equally because the concentrations are equal. So here in an isotonic solution, so water is going in and out at the same rate because they're evened out. Hypotonic solution, water enters the cell. Hypertonic solution, water leaves the cell. So make sure you understand these processes of osmosis so remember the solute concentration in versus outside of the cell determines the movement of water and keep in mind osmosis movement of water only is what it's describing okay active processes there are a few different active processes that we'll learn about later on but mainly it's active transport So anytime something is actively transported, that means that it not only requires a transporter protein like the channels, like the protein channel we looked at earlier, but it also requires ATP. So remember how I said diffusion is going, is solutes moving down their concentration gradient, right? Normally going from high to low. In active transport, molecules or solutes go from an area of low to high. high. So we call that going against the gradient, going against the natural flow of things, which again requires ATP energy. So let's discuss some other parts of a bacterial cell. So we described the cell membrane, all of the stuff that go on in the cell membrane, the processes, but the substance inside the plasma membrane, inside of a cell, is called the cytoplasm. The cytoplasm is mostly made up of water, but it also has something called cytoskeleton. Cytoskeleton inside of the cell is basically different types of proteins, different types of protein filaments working together to not only maintain the shape of the cell, so the cell doesn't just like collapse, but also it's important for movement. The movement of the cell itself as a whole and also movement within the cell, like maybe one molecule or compound or protein, whatever, has to move from one side of the cell to another part of the cell, cytoskeletal proteins have to move from one side of the cell to another part of the cell. help this happen. Now we mentioned that first of all the bacterial chromosome is circular, right? And we also mentioned that prokaryotic cells like bacterial cells do not have organelles. So where is the DNA in a bacterial cell? Well it's actually this area. So it's not really an organelle, it's not enclosed with anything, it's not like a separate room, but it's like one section of the cell, like one area of the cell. And that's where then that's called the nucleoid and that's where that circular bacterial chromosome is So it's not that the bacterial chromosome is just like floating around the cytoplasm. It's still in one place It's just not in like a covered organelle ribosomes are another important part inside of a bacterial cell and Ribosomes are where proteins are produced. So sites of protein synthesis. Remember synthesis means like production or creation. And ribosomes are made up of two things. They're composed of protein and they're composed of ribosomal RNA. There are different types of RNA and one type of RNA is called rRNA or ribosomal RNA. And so together these work to make proteins for the cell. And a prokaryotic ribosome looks like this. A prokaryotic ribosome has two subunits that come together. There's the small subunit and the large subunit. The small subunit is also called the 30S subunit. The large subunit is also called the 50S subunit. And so together, this is called the 70S ribosome. So this is what a prokaryotic ribosome looks like. Eukaryotic ribosome, a little bit different. All right. Now there are also these structures called endospores. This is really really important because some genre of bacteria, and genre is plural for genus, some genre of bacteria including bacillus and clostridium that do cause disease in us, are able to make these structures called endospores. And what endospores are is that they are resting cells. So they're basically like a version of a cell and it's produced when there's no more nutrients and a bacterial cell is going to die out. So let's say for example I have some bacillus cells okay and they go to an environment and the environment is fine but then the nutrients in the environment start to basically be depleted and finish and so now they're like okay we have no more nutrients like we have no way of surviving. They're able to now say okay So we're going to die out, but they're able to produce these resting kind of dormant type cells called endospores. And endospores are really, really resistant to a lot of things. Like they're really hard to destroy. So they're resistant to heat. They're resistant to any chemicals, chemical disinfectants, any radiation. I call them apocalypse resistant. They can basically survive with no nutrients for like... thousands, millions of years. And then any time the conditions are right again, they'll turn into a regular functioning cell. And so bacillus and clostridium are able to make these endospores. They're like the main two examples that we're going to look at for endospores. So whenever a cell is dying out and it starts making endospores, that's called sporulation. So the process of forming endospores is called sporulation. And whenever the endospore is in the right environment again, and it can return back to its vegetative, functioning, reproducing, active self, that process is called germination. So here's a bacterial cell with an endospore inside of it. So if you look at this process, and we don't have to know the details of it, but just let's look at the overview and get this visual of it. So here's a cell, and it's about to die out. So what it does is it kind of copies its DNA You can see it kind of borders off this edge and then forms this endospore Endospore will mature it'll have all of its qualities that'll make it like apocalypse resistant And then it's released that endospore is released and it kind of just lays dormant for years and years and years Until the conditions are right and then it'll germinate and this cell just dies out. Okay And we'll revisit endospores later on again. And again, you don't have to know the details of this, but you do have to know that other slide with the bullet points on it. Okay, we're now going to shift gears to eukaryotic cells. There isn't as much information on this one for this PowerPoint compared to the bacterial cells. But one of the characteristics of eukaryotic cells that made them different from prokaryotic cells are the organelles. So there's a lot of organelles inside here. There's the nucleus, there's the golgi, there's the endoplasmic reticulum. Now, some eukaryotic cells have flagella, some have cilia. So if you recall, flagella was really important for movement, for locomotion, for moving things. And so flagella can also be found in eukaryotic organisms. And another type of external structure that's used for motility are called cilia. So these are shorter. They're more like hair-like structures, and there's way more of them. So here you can see eukaryotic flagellum. There's usually very few in number when we're talking about eukaryotic cells, and it's longer. And then here are cilia. So cilia are all over hair-like structures, shorter, but way more of them. And again, these are both used for motility and movement. The cytoplasm of a eukaryotic cell, again, it's the substance inside. The fluid portion of the cytoplasm inside of the cell is called the cytosol. And eukaryotic cells also have a cytoskeleton. Like I mentioned, these are these protein filaments. They're called microfilaments, intermediate filaments, as well as microtubules. These are all part of the cytoskeleton. It gives shape to the cell, it supports the cell, and it's also important for movement of the cell itself, as well as movement within the cell. Ribosomes, same thing as prokaryotic cells, ribosomes are the sites of protein synthesis inside eukaryotic cells. The nucleus is one of the membrane-bound organelles, meaning that it has a membrane surrounding it. And the nucleus... actually has a double membrane. So it has two membranes surrounding it, and we call that the nuclear envelope. And of course, that's where the DNA is located and protected. So DNA has to be very protected. So that double membrane is part of that protection. There's also the endoplasmic reticulum. It's this folded transport network. Proteins move along the endoplasmic reticulum. And there's two types of ER. There's the rough and the smooth endoplasmic reticulum. So the rough ER is actually called rough because it has a rough appearance to it, because it has ribosomes all over it. So it's like studded with ribosomes. And so the rough ER is where protein synthesis occurs with the help of ribosomes. So you can see here, this is the rough ER. And I want you to also notice that it kind of... follows the nuclear membrane. It's kind of attached. It's like the continuation of the membrane of the nucleus. And here you can see all these little ribosomes all over it, giving it that rough textured appearance. The Smoothie R does not have any ribosomes over it, so that's why it has like a smooth appearance to it. And it has a lot of functions, but the function that we need to know is that it is important for lipid synthesis. So here's the smooth ER which continues off of that rough ER. Okay, the Golgi complex, or maybe you called it a Golgi apparatus before, this is a transport organelle. So this is also one of the organelles in a eukaryotic cell, and it helps modify proteins. So for example, we mentioned that proteins are made in the rough ER, and then they are transported to the Golgi apparatus. And the Golgi apparatus basically helps the proteins mature. It modifies the proteins and packages it up and gets it ready for basically sending it out. So I always call the Golgi kind of like the shipping station and the packaging station. So it kind of finalizes that protein and it kind of puts a shipping label on that protein. So that protein goes to its correct destination. Maybe the protein is going to go to the cell membrane and become a channel protein. Maybe the protein is going to be one of the proteins of the cytoskeleton. maybe it's going to be part of a ribosome. So depending on what that protein's function is, it'll transport that modified proteins. And it does this through vesicles. Vesicles, think of them as little bubbles, kind of carrying those proteins to wherever that protein is supposed to go. Maybe the protein is defective. Maybe it didn't fold correctly and we have to get rid of it. Then it'll send it somewhere to be degraded. So here's the Golgi apparatus. proteins come in from the er and then they're modified and then they get sent out in these little vesicles to whatever their final destination is so another really important organelle here is the lysosome the lysosome um is basically where i call it like the cleanup crew the cleanup station of the cell dead parts of organelles dead organelles, dead proteins, things that have to be broken down, even like if there's a bacteria in there, pieces of bacteria in there, it's kind of like the trash cleanup system. Inside of a lysosome, and remember this is a membrane-bound organelle, which is really important and I'll explain why in a moment, inside of the lysosome there are digestive enzymes, meaning enzymes that break things down. So they'll break things down. kind of like break down any trash and get rid of that trash and kind of send it out of the cell. And so it's really important that lysosomes have that membrane around it because what happens if it didn't? The digestive enzymes would basically leak out and they would start breaking down and basically killing all the parts of the cell and the cell would end up dying. Okay. The mitochondria is another important one. Just like the nucleus, the mitochondria also has a double membrane surrounding it. It contains these folds on the inside, which we'll look at in a second, called cristae. And in the middle of the mitochondria, there is a fluid portion called the matrix. We sometimes call that the mitochondrial matrix or the matrix of the mitochondria. And the function of the mitochondria is ATP production, or in other words, cellular respiration. So it makes energy for the cell. So this is what that mitochondria looks like. So you could see these little folded parts, these zigzag parts that are kind of sticking out here. That's the cristae. And then in the middle is the matrix. And again, there's the outer membrane and the inner membrane. So you can see those two layers of the membrane of the mitochondria. Another organelle that some eukaryotic organisms or eukaryotic cells have is chloroplasts. Chloroplasts are where photosynthesis occurs. And there's like these flattened membranes that make it up. And those are called thylakoids. And within that flattened material, that's where chlorophyll is. Those are the pigments. And so this is what that looks like. So here we have the thylakoids, kind of like these folded. things right here and then there's chlorophyll inside there okay the last organelle we want to talk about are peroxisomes now peroxisomes are kind of similar to lysosomes but they're different because they destroy hydrogen peroxide specifically so hydrogen peroxide which is here symbolized as h202 we don't really think of it as a bad thing right we can use hydrogen peroxide as like an antiseptic it kills things right it's helpful for us however hydrogen peroxide is toxic to the cells themselves so we have organelles called peroxisomes again membrane-bound organelles called peroxisomes that can actually break down hydrogen peroxide therefore detoxifying it and protecting the cell so it's kind of similar to lysosomes but peroxisomes are specific to destroying hydrogen peroxide. Now, the last thing we're going to discuss is this theory, this concept called the endosymbiotic theory. And this basically is a theory that explains how eukaryotes basically evolved. Because back in the day, millions, millions of years ago, we all started with the same... prokaryotic organism. These tiny prokaryotic organisms. So there were no eukaryotes back in the day. So how did eukaryotes develop? So what happened is, this is what the endosymbiotic theory states, is that larger prokaryotic or larger bacterial cells engulfed or ate up smaller bacterial cells. And those smaller bacterial cells ended up becoming the organelles. of that big bacterial cell and this was the development of the first ever eukaryotic cells and so there are two major examples that prove the endo symbiotic theory chloroplasts and mitochondria these are two organelles that we just learned about and when we know about in eukaryotic cells that were actually their own organism so chloroplasts was its own bacterial cell mitochondria was its own bacterial organism on its own but they were engulfed by a larger bacterial cells and they ended up having the symbiotic relationship with the bigger cell so the bigger cell provided them with shelter with protection and they in turn provided the cell with energy so they ended up having this symbiotic relationship and this is how eukaryotes were originated and evolved. So really really early on we all came from the same early organism and then we had different types of bacteria right? We had larger bacteria and we had smaller bacteria. So you can see that the larger bacteria ate up the smaller bacteria. and the smaller bacteria became an organelle that provided energy for it. So this is the evolution and development of the eukaryotic cell.

and some of the organelles that are found in eukaryotic cells and their functions. And then some of it is going to be new information about bacterial cells that we'll be using until the end of the semester. So first, let's look at the differences between prokaryotic cells and eukaryotic cells.

So eukaryotic cells, let's look at that first. The chromosomes in eukaryotic cells are paired chromosomes. They are found in the nucleus.

which is one of the organelles eukaryotic cells have organelles inside of them and eukaryotic cells divide by mitosis so from previous biology courses you have probably learned about mitosis which is basically how cells divide and double and so on now the prokaryotic cells actually have one circular chromosome so For example, eukaryotic chromosomes, they kind of look like this if you've ever seen them, right? They're paired chromosomes. Whereas prokaryotic chromosomes, it's like one circular chromosome, so it looks pretty different.

So whenever we look at bacterial chromosomes, we're going to notice that it has a circular DNA because remember bacteria are prokaryotes. Prokaryotic cells also are prokaryotes. do not have organelles so their genetic material is not in the nucleus there's no nucleus it's just somewhere inside the cell also bacteria have cell walls made up of peptidoglycan which we've learned before and they divide by binary fission which is budding so one cell will slip into two cells and that's how they move on from one generation to the next generation and so on So we're going to first look at prokaryotic cells, specifically bacteria. So first let's discuss bacterial cells size.

So the average size of a bacterial cell is 0.2 to 2.0 micrometers. Okay, so it's really, really, really small. And so we're going to look at that, and obviously we started looking at bacteria with the microscope, and we know that they're really, really, really tiny. Most bacteria are considered to be monomorphic, meaning they are just one single shape. So, for example, all the bacterial cells of Staphylococcus aureus are all going to be circular in shape, or all bacterial cells of E.

coli are going to be elongated. So usually they're just one single shape. So now we have to learn the vocabulary of what these shapes are. So this is really, really important.

And this is something we carry on throughout the whole semester. So if bacterial cells are rod shapes, they kind of look long like a rod. We call that bacillus. So the shape is bacillus. That's the correct term.

If it's spherical or round or circular shaped, we call that caucus. Now some bacterial cells are actually kind of spiral or they kind of are like wiggly. We can call them vibrio or spirochetes.

So spirochetes, that shape is like a coiled shape, kind of like a corkscrew shape. And vibrio is a comma shape, so it kind of looks like a curved rod. So if you look here, here's vibrio and then here's a spirochete, which we'll talk about. It'll come up again this semester.

Now the arrangement is also important when we're looking at bacterial cells. So if bacterial cells are in pairs, so they're just like two together, we call that diplo. In clusters, we say staphylo.

If they're in chains, we say strepto. And if they're in four groups of fours, we call that tetra. Depending on the shape and the arrangement, we would call it one of these words.

So for example, if I have pairs of rod-shaped cells, I would call it diplobacilli. If I have chains of circular spherical cells, I would call it streptococci. So this is what that looks like. So here you could see that they're in pairs, right, and then it's circular in shape.

Tetrad is four of them. Remember, staphylo is just a group of them, like a cluster of them all together. And same thing applies for bacillus.

So here are those bacillus shaped cells that are elongated. Now there are some species of bacteria that their rods are so tiny that they kind of look like spheres. And so that's one that we have to be careful of because that one is really hard to tell when we look through the microscope. Here again diplobacilli. So here we have pairs of them and then here are chains of them.

Okay so sometimes it's going to give you information about the shape of or it's going to give you information about what that cell is going to look like. So for example staphylococcus we know that Those cells are going to be spherical. We also have a genus called Bacillus.

The Bacillus genus, what shape do we think that all of the cells have? They're going to have a Bacillus shape. So there's one called Bacillus anthracis.

That's the bacterium that causes anthrax, if you've ever heard of anthrax before. And you can see that it's chains of these Bacillus shaped or rod shaped cells. So Any species under the bacillus genus is going to be bacillus shaped.

So that was just an example. Okay, now let's look at structures that are outside of the cell wall, kind of exterior structures of bacterial cells. One of them is called the glycocalyx. When you see glyco, think of carbohydrates.

So glycocalyx is like this layer of polysaccharide, but it could also be... made of protein but most of the time it's made up of carbohydrates it's outside of the cell wall kind of like an extra layer external to the cell wall and it has this like jelly-like consistency this thick viscous consistency and there are two examples of a glycocalyx a capsule and the slime layer so a capsule we call it a capsule if it's really organized and it's really um it's bound very tightly to the cell wall and if it's kind of loose and undisorganized we call it a slime layer so here you can see an example so this is of streptococcus pneumoniae and you can see that you have the cells and then you have the outside and then here in like this aqua this aqua layer right here that would be a capsule okay flagella some bacteria are motile, so they have motility. So they may have flagella that helps them travel and move. So flagella is really, really advantageous to bacteria.

Again, it's an external structure kind of sticking out of the cell, and it helps propel bacteria to a favorable environment. So if a bacteria likes to move toward an environment that they like or away from an environment that's not favorable, that they don't like, this is called taxis and flagella are able to provide bacteria the taxis to move towards things that they like and away from things that they don't like. So this is like a really detailed image of what a flagellum consists of.

So flagellum is singular, flagella is plural. So here you can see there's some flagella kind of sticking out of the cell wall of the bacteria. and you can see how complex the structure is and it uses atp because it has to be able to move okay now flagella can be arranged differently so there are different arrangements of flagella for example if the flagella is all over the bacterial cells like it's all around kind of like it's all covered in hair we call that peritrichous arrangement if it's just at the ends of the bacterial cell we would call it amphitrichous or we would call it polar flagella. Now sometimes a bacterial cell just has one single flagella, sometimes they have like ten flagella but it's still just on one end, so there's different arrangements of bacterial flagella. Now another structure that kind of Looks like flagella in the beginning, but it's not.

This is called axial filaments. Axial filaments are located only in spirochete cells. So if you recall, spirochete cells, they had that coiled like corkscrew structure, kind of that spiral look to them. Axial filaments are kind of like an extension, kind of sticking out of the cell. However, they kind of circle back around the cell and they kind of twist it.

So think of you. twisting a strand of hair and kind of turning it into like this corkscrew or coil-like structure. That's what the axial filament does.

It kind of circles back on the cell, wraps around the cell, and causes it to have this coiled-like appearance, which is really, really helpful to the bacteria because it helps the bacteria navigate and go through areas that are super viscous, super thick. That shape, that corkscrew shape, helps it survive in those areas. so this is what it looks like so here's that axial filament it wraps back around the spirochete causing it to have that spiral shape okay there are also these um structures called fimbriae and pili fimbriae are these hair-like structures and they're really important for attachment pili are also used for attachment but they're also involved in motility So this is what fimbriae looks like.

So you can see these kind of like hair-like structures sticking out. And it's important if this bacterial cell finds an environment that it really likes, or in other words, a favorable environment, they can attach to whatever that surface is. So pili, we're going to look at a little bit more later on, but they are both for attachment and for motility. Okay, what about the cell... wall.

The cell wall of bacteria is very, very, very protective. Not only does it protect the cell membrane of the bacterial cell, it also prevents osmotic lysis. This is when too much water fills up in a cell and it causes the cell to kind of blow up, blow up, blow up, and swell so much that it can burst and basically die.

Now, if you recall, the cell wall of bacterial cells is made up of peptidoglycan. So now we're going to go into detail as to what peptidoglycan is. What is that? So peptid, peptide, what do you think of when you see this? You think of protein.

Glyco or glycan, you think of carbohydrates. And that's what peptidoglycan is. It's this really complex compound that's made up of proteins and carbohydrates.

So first, let's talk about the carbohydrates. So there are these repeating disaccharides in these rows called NAG and NAM. So NAG stands for N-acetylglucosamine. NAM stands for N-acetylmuramic acid.

You don't have to know the full word, but you should know NAG and NAM. So it's kind of like a pattern of repeating units. So it's like NAG, NAM, NAG, NAM, NAG, NAM.

It's like one and then the other. Kind of these repeating, and there's like these rows of these. carbohydrates and the rows of the carbohydrates are linked together they're connected to each other by protein bridges or in other words polypeptides so sorry i moved my screen okay so here we have the nag and the nam so here's the nag nam and so it would be nag nam nag nam and so on you have these kind of like these chains of carbohydrates so this is what it looks like so nagnam nagnam all the way through and you have these chains of them these rows of carbohydrates and here between the carbohydrates you have peptide bridges protein bridges basically linking them together and it kind of makes like this cage-like appearance and that's literally what this cell wall is that surrounds the outside of the cell membrane now when we're thinking about the cell wall of bacteria It brings us to two categories of bacteria. Some bacteria are known as gram-positive bacteria, and some bacteria are known as gram-negative bacteria. So what does this mean?

This has to do with the cell wall of the bacteria. So it's these two big categories of gram-positive or gram-negative. So gram-positive cell walls have a very thick peptidoglycan.

They have many, many multiple layers of this peptidoglycan, whereas gram-negative cell walls have just one single layer of peptidoglycan, so they have thinner cell walls. However, gram-negative cells also have an extra cell membrane. So not only do they have the cell membrane, the typical cell membrane of the bacterial cell, then they have one layer of peptidoglycan, and then they have an outer membrane surrounding it. So the space between the inner or typical cell membrane and the outer membrane is known as the periplasmic space or the periplasm. So let's take a look here.

Here, just by looking at it, I would already see that this is a gram positive bacterial cell wall because I have multiple layers of peptidoglycan. Another thing I would notice is that there's no outer membrane, right? That's only specific to gram negative. Looking at this image right here, I could tell that it's a gram. negative bacterial cell because I have the cell membrane.

I have one single layer of peptidoglycan and then I have that outer membrane here. Now something really important that we have to know about the outer membrane of gram negative bacteria is that there's something in there called lipopolysaccharides. So these blue structures that are embedded in that outer membrane are called lipopolysaccharides.

called lipopolysaccharide LPS so lipo refers to lipids polysaccharide of course it's a carbohydrate so this is made up of a type of polysaccharide and a type of lipid so the polysaccharide is called a polysaccharide the lipid is called lipid a I want you to remember LPS is toxic it's considered what we call an endotoxin, which we'll revisit later on in a later chapter this semester, but LPS is very toxic. So if, for example, oh, and before I say my example, the toxic part of LPS is the lipid A, that's the part that's toxic. So if, for example, I have an infection by a gram-negative bacteria, so the bacteria that's infecting me is gram-negative.

If you use a certain antibiotic to basically kill the bacterial cell and that antibiotic causes this outer membrane of the bacterial cell to basically break up or burst That means that LPS gets released and that's really dangerous because LPS is toxic to us So it would end up causing septic shock and a bunch of other things in the body. So it's really it could be fatal Okay, so how can I find out if I'm working with a bacterium in lab and I want to find out is this bacterium a gram-positive or a gram-negative bacterium? So we do gram staining. You might hear my dog bark sometimes.

So what you do to figure out if it's gram-positive or negative, you do... gram staining. So it's a staining method. We don't have to learn the details of this. The details of this we'll learn when we're in lab.

But after you do the gram staining on the bacteria, if your bacterial cells end up being stained purple, they're gram positive. If they end up being stained red or pink, they're gram negative. So if you look at a gram stain, and after the gram staining method, you look at your microscope slide, if it's purple, it's gram positive if it's pink or red it is gram negative okay so there are also cell walls that are different and unique so we call these atypical cell walls and one of the main examples of a unique or atypical cell walls are acid fast cell walls acid fast bacteria have a unique cell wall because they have this waxy lipid called mycolic acid bound to the peptidoglycan. So they basically have mycolic acid, this specific compound, this specific lipid inside of their cell wall that makes them different. It's really helpful and advantageous for them.

We'll revisit this later on. But a type of bacterium, genus of bacteria that has acid-fast cell walls are mycobacterium. So if you've ever heard of... Mycobacterium tuberculosis, it causes tuberculosis.

This one is considered an acid-fast bacteria. So it's not positive or negative, it's a different category. Now for this one, you can't really do gram staining on it, so you do another staining method in lab called acid-fast staining.

So this is another one that the steps of this we'll learn in lab, but this is what it looks like. If I want to figure out if, let's say I want to figure out if mycobacterium tuberculosis is acid fast or not acid fast, I would do this whole staining method. And if I end up getting cells that are stained like this fuchsia hot pink color, that's positive. That means yes, it is acid fast. If I end up getting blue, then it would be not acid fast.

Our next example of having an atypical cell wall. are the mycoplasmas. This genus of bacteria don't even have a cell wall.

They lack cell walls. That's because they have undergone something called reductive evolution, okay? And reductive evolution or degenerative evolution, this is when it's kind of like if you don't use it, you lose it. They've lost the need to have a cell wall because they live inside the host, so they're already kind of protected.

And so they've evolved to not even have a cell wall anymore. So pretty interesting. Now, there are also structures we have to talk about that are inside the cell wall, inside of the cell.

So obviously, there's the plasma membrane. The plasma membrane is very, very protective. It has a lot of functions.

And we've learned that it's made up of a phospholipid bilayer, or in other words, two layers of phospholipids, right? and that's the main component of the plasma membrane or the cell membrane. But there are also proteins that are embedded inside of that cell membrane, and they're very, very helpful in the functioning of the cell membrane.

Now, there are two types of proteins. There are proteins called peripheral proteins that they only stay on one layer, like one side of the cell membrane. And then we also have integral or transmembrane proteins that penetrate the membrane and they basically are embedded really deeply and on both sides of that bilayer. So here is my phospholipid bilayer of my cell membrane, and I have peripheral proteins just on one side of the layers, and then I can have integral proteins or transmembrane proteins kind of spanning that entire plasma membrane.

Now there's something called the fluid mosaic model. The fluid mosaic model basically tells us that it's not just phospholipids that make up the cell membrane right there are proteins in there and it's also fluid so there's movement there phospholipids can rotate they can move laterally proteins can move from one spot to another spot and the membrane is lipid-like another cool thing about the plasma membrane is that it is self-sealing so if it opens up it'll seal right back up so it's fluid. So we call that the fluid mosaic model.

So what are the functions of the plasma membrane? A really important function or quality of the plasma membrane is selective permeability. Selective permeability basically describes the plasma membrane's function of allowing some molecules to go through and not others.

So it is selective in what can enter and or exit a cell. And so how do molecules actually enter and exit the cells? So there are two kind of big general categories.

These are called passive processes and active processes. Now in a passive process, just think of it, it's passive, it's just relaxed, it does not require any energy. This is when substances move from an area of health. high concentration to an area of low concentration.

And whenever you hear the word concentration, think of level or amount. So for example, if I have salt and it wants to move, well, let me use another analogy. So let's say we are in a classroom, okay?

We're in a classroom and we have 50 students in our classroom, but I have a classroom next door. that's only three students in there or five students in there, let's say. What would I ask you to do?

What was like the first thing I would think to do? I would think to kind of split up the class, right? I would ask some of us to move to the other classroom. So we went from an area of high concentration of students to an area of low concentration of students, okay?

That's a passive process. An active process would be the opposite. So this is when substances move from low concentration area to a high concentration area. And in order to do this, this is kind of like against the natural flow of things.

And so since you're going against that natural flow, you need energy. So active processes, they're called active because they require energy. So that would be instead of the first thing that would come to mind is, hey, let's even out the classes.

If let's say I told those five students to enter our class and now I have even more students. That's going from an area of high of high sorry that's going from an area of low concentration to an area of high concentration so you're going against that natural flow of things which is why atp energy is required for active processes so we're first going to talk about passive processes because there are a few different types of passive processes one example of a passive process is called simple diffusion Simple diffusion is basically what I described when I was describing a passive process. So it's a movement of a solute from an area of high concentration to an area of low concentration. And this is to reach something called equilibrium.

So this is to reach basically balancing out. So when we're talking about the inside of the cell versus the outside of the cell, let's say the inside has a lot of salt and the outside doesn't. In simple diffusion, the salt will basically diffuse outside of the cell until the inside and the outside are equaled out or balanced out and that's equilibrium that's simple diffusion and it's a passive process so it does not require any energy so let's say in this example this is the lipid bilayer or in other words the cell membrane right here's outside of the cell and here's inside of the cell we have a lot more on the outside compared to the inside. So what will simple diffusion do? Going from high concentration to a low concentration.

So in this case, molecules or solutes will travel inside. We call this going down the concentration gradient. Anytime you have a difference in concentration outside versus inside of a cell. it creates a gradient.

In this case, it's a concentration gradient. That means there's an unequalness going on here. And so if I say that solutes are traveling down their concentration gradient, this is what I mean, going from high concentration to low concentration. Now there's another type of diffusion called facilitated diffusion. Facilitated diffusion is the same thing, except the solutes need a little bit of help.

So they'll usually combine with a transporter protein. They basically need someone to kind of carry them through the cell membrane. This is if the molecule is a larger molecule, it's going to have a harder time passing through.

If the molecule is charged, like a charged ion, that's going to be harder to go through with that concentration gradient. So here's an example of that. So here's the bilayer and here's a protein, like an integral protein or transmembrane protein.

And it serves as either like a channel or a carrier. So we're still moving down the concentration gradient, but we just need a little bit of help going through. But still, no energy is used. So there's some facilitation going on.

So it's facilitated diffusion. Okay, another type of passive process is osmosis. Now, when you think of osmosis, think of the movement of water.

So the movement of water across that selectively permeable cell membrane from an area of high water to an area of lower water concentration. Now, water does this a little differently. There are these tiny little water channels.

They're literally like little holes for water. And we call those aquaporins. Aquaporins basically like water pour. Okay, so aquaporins are all over the cell membrane. and water can go through it to either enter the cell or exit the cell either direction and this is by osmosis again another type of passive process so no energy is needed but water is also going to want to balance out so it's going to want to balance out like the ratio between water and solute or in other words the ratio between solvent and solute so if i have a lot of salt on one side water is going to follow wherever you have too much salt to kind of balance out that water salt ratio.

Now I want you to keep one thing in mind and write it down if you need to. Water always follows salt and I'm using salt as an example here but it's any type of solute. It could be sugar, it could be anything else.

Water always follows salt so wherever there's a lot of salt or a lot of solute, water is going to go there okay to kind of balance that out. So there's also something called osmotic pressure, and that's the pressure that's needed to stop the movement of water across the membrane. So depending on where I have a lot of solute and where I have a lot of water, that's going to determine the movement of osmosis so once again water follows salt so depending on where i have a lot of solute that's the direction water is going to go that's going to determine hey is water going to enter the cell or is water going to exit the cell so there are three situations that can happen three different types of solutions so if this is a cell right here So this little baggie, it serves as a cell. And then here's the solution that surrounds it. So you have like a beaker of solution and the cell is inside of it.

Depending on if there's a lot of solute in that solution or a little bit of solute, that's going to determine the movement of water. So three types of solutions that we have to look at. We have isotonic, hypotonic, and hypertonic.

So let's first talk about hypertonic solutions. means what? Hyper means a lot, right?

Or really high or a lot, like a big amount. So in a hypertonic solution, I have a really high solute concentration compared to inside of the cell. Or in other words, in a hypertonic solution, there's a lot more solute in the solution compared to inside of the cell. So what direction is water going to move? So if my cell is in a hypertonic solution where there's a lot more salt in the solution compared to inside of the cell, water is going to move out of the cell.

Remember, it's going to follow wherever there's more solute. So water will leave the cell. And what happens if a bunch of water leaves the cell?

The cell kind of shrinks and shrivels up. And then the opposite is true. In a hypotonic solution, hypo means low or below. So a hypotonic solution has way less solute or lower solute concentration compared to the inside of the cell.

So where is water going to go? Water is going to go where there's more solute. In this case, there's relatively more solute inside of the cell. So when a cell is placed in a hypotonic solution, water enters the cell. Water moves into the cell.

And so what would happen to the cell if water keeps entering it? It's going to swell up so much that it can possibly burst, or in other words, lyse. So what if there's an isotonic solution?

Iso means same. So in an isotonic solution, the solute concentration outside is equal to the solute concentration inside. So then what does water do in that case when one is not higher than the other? You might think at first, it's natural to first think that, okay, then water doesn't move anywhere.

It doesn't move out and it doesn't move in because it doesn't need to. However, keep in mind that water is always moving in and out of the cell. Water doesn't just stop doing it.

So actually, the rate or the amount of water entering the cell is balanced with or equal to water exiting the cell. So the water is at equilibrium. So it's not that it's not moving at all. It's just moving equally because the concentrations are equal.

So here in an isotonic solution, so water is going in and out at the same rate because they're evened out. Hypotonic solution, water enters the cell. Hypertonic solution, water leaves the cell.

So make sure you understand these processes of osmosis so remember the solute concentration in versus outside of the cell determines the movement of water and keep in mind osmosis movement of water only is what it's describing okay active processes there are a few different active processes that we'll learn about later on but mainly it's active transport So anytime something is actively transported, that means that it not only requires a transporter protein like the channels, like the protein channel we looked at earlier, but it also requires ATP. So remember how I said diffusion is going, is solutes moving down their concentration gradient, right? Normally going from high to low. In active transport, molecules or solutes go from an area of low to high.

high. So we call that going against the gradient, going against the natural flow of things, which again requires ATP energy. So let's discuss some other parts of a bacterial cell. So we described the cell membrane, all of the stuff that go on in the cell membrane, the processes, but the substance inside the plasma membrane, inside of a cell, is called the cytoplasm. The cytoplasm is mostly made up of water, but it also has something called cytoskeleton.

Cytoskeleton inside of the cell is basically different types of proteins, different types of protein filaments working together to not only maintain the shape of the cell, so the cell doesn't just like collapse, but also it's important for movement. The movement of the cell itself as a whole and also movement within the cell, like maybe one molecule or compound or protein, whatever, has to move from one side of the cell to another part of the cell, cytoskeletal proteins have to move from one side of the cell to another part of the cell. help this happen. Now we mentioned that first of all the bacterial chromosome is circular, right? And we also mentioned that prokaryotic cells like bacterial cells do not have organelles.

So where is the DNA in a bacterial cell? Well it's actually this area. So it's not really an organelle, it's not enclosed with anything, it's not like a separate room, but it's like one section of the cell, like one area of the cell. And that's where then that's called the nucleoid and that's where that circular bacterial chromosome is So it's not that the bacterial chromosome is just like floating around the cytoplasm. It's still in one place It's just not in like a covered organelle ribosomes are another important part inside of a bacterial cell and Ribosomes are where proteins are produced.

So sites of protein synthesis. Remember synthesis means like production or creation. And ribosomes are made up of two things. They're composed of protein and they're composed of ribosomal RNA.

There are different types of RNA and one type of RNA is called rRNA or ribosomal RNA. And so together these work to make proteins for the cell. And a prokaryotic ribosome looks like this. A prokaryotic ribosome has two subunits that come together.

There's the small subunit and the large subunit. The small subunit is also called the 30S subunit. The large subunit is also called the 50S subunit.

And so together, this is called the 70S ribosome. So this is what a prokaryotic ribosome looks like. Eukaryotic ribosome, a little bit different.

All right. Now there are also these structures called endospores. This is really really important because some genre of bacteria, and genre is plural for genus, some genre of bacteria including bacillus and clostridium that do cause disease in us, are able to make these structures called endospores. And what endospores are is that they are resting cells. So they're basically like a version of a cell and it's produced when there's no more nutrients and a bacterial cell is going to die out.

So let's say for example I have some bacillus cells okay and they go to an environment and the environment is fine but then the nutrients in the environment start to basically be depleted and finish and so now they're like okay we have no more nutrients like we have no way of surviving. They're able to now say okay So we're going to die out, but they're able to produce these resting kind of dormant type cells called endospores. And endospores are really, really resistant to a lot of things. Like they're really hard to destroy. So they're resistant to heat.

They're resistant to any chemicals, chemical disinfectants, any radiation. I call them apocalypse resistant. They can basically survive with no nutrients for like... thousands, millions of years.

And then any time the conditions are right again, they'll turn into a regular functioning cell. And so bacillus and clostridium are able to make these endospores. They're like the main two examples that we're going to look at for endospores. So whenever a cell is dying out and it starts making endospores, that's called sporulation. So the process of forming endospores is called sporulation.

And whenever the endospore is in the right environment again, and it can return back to its vegetative, functioning, reproducing, active self, that process is called germination. So here's a bacterial cell with an endospore inside of it. So if you look at this process, and we don't have to know the details of it, but just let's look at the overview and get this visual of it. So here's a cell, and it's about to die out.

So what it does is it kind of copies its DNA You can see it kind of borders off this edge and then forms this endospore Endospore will mature it'll have all of its qualities that'll make it like apocalypse resistant And then it's released that endospore is released and it kind of just lays dormant for years and years and years Until the conditions are right and then it'll germinate and this cell just dies out. Okay And we'll revisit endospores later on again. And again, you don't have to know the details of this, but you do have to know that other slide with the bullet points on it.

Okay, we're now going to shift gears to eukaryotic cells. There isn't as much information on this one for this PowerPoint compared to the bacterial cells. But one of the characteristics of eukaryotic cells that made them different from prokaryotic cells are the organelles.

So there's a lot of organelles inside here. There's the nucleus, there's the golgi, there's the endoplasmic reticulum. Now, some eukaryotic cells have flagella, some have cilia.

So if you recall, flagella was really important for movement, for locomotion, for moving things. And so flagella can also be found in eukaryotic organisms. And another type of external structure that's used for motility are called cilia. So these are shorter.

They're more like hair-like structures, and there's way more of them. So here you can see eukaryotic flagellum. There's usually very few in number when we're talking about eukaryotic cells, and it's longer.

And then here are cilia. So cilia are all over hair-like structures, shorter, but way more of them. And again, these are both used for motility and movement.

The cytoplasm of a eukaryotic cell, again, it's the substance inside. The fluid portion of the cytoplasm inside of the cell is called the cytosol. And eukaryotic cells also have a cytoskeleton. Like I mentioned, these are these protein filaments. They're called microfilaments, intermediate filaments, as well as microtubules.

These are all part of the cytoskeleton. It gives shape to the cell, it supports the cell, and it's also important for movement of the cell itself, as well as movement within the cell. Ribosomes, same thing as prokaryotic cells, ribosomes are the sites of protein synthesis inside eukaryotic cells. The nucleus is one of the membrane-bound organelles, meaning that it has a membrane surrounding it. And the nucleus...

actually has a double membrane. So it has two membranes surrounding it, and we call that the nuclear envelope. And of course, that's where the DNA is located and protected.

So DNA has to be very protected. So that double membrane is part of that protection. There's also the endoplasmic reticulum.

It's this folded transport network. Proteins move along the endoplasmic reticulum. And there's two types of ER. There's the rough and the smooth endoplasmic reticulum. So the rough ER is actually called rough because it has a rough appearance to it, because it has ribosomes all over it.

So it's like studded with ribosomes. And so the rough ER is where protein synthesis occurs with the help of ribosomes. So you can see here, this is the rough ER. And I want you to also notice that it kind of...

follows the nuclear membrane. It's kind of attached. It's like the continuation of the membrane of the nucleus. And here you can see all these little ribosomes all over it, giving it that rough textured appearance. The Smoothie R does not have any ribosomes over it, so that's why it has like a smooth appearance to it.

And it has a lot of functions, but the function that we need to know is that it is important for lipid synthesis. So here's the smooth ER which continues off of that rough ER. Okay, the Golgi complex, or maybe you called it a Golgi apparatus before, this is a transport organelle.

So this is also one of the organelles in a eukaryotic cell, and it helps modify proteins. So for example, we mentioned that proteins are made in the rough ER, and then they are transported to the Golgi apparatus. And the Golgi apparatus basically helps the proteins mature.

It modifies the proteins and packages it up and gets it ready for basically sending it out. So I always call the Golgi kind of like the shipping station and the packaging station. So it kind of finalizes that protein and it kind of puts a shipping label on that protein. So that protein goes to its correct destination. Maybe the protein is going to go to the cell membrane and become a channel protein.

Maybe the protein is going to be one of the proteins of the cytoskeleton. maybe it's going to be part of a ribosome. So depending on what that protein's function is, it'll transport that modified proteins.

And it does this through vesicles. Vesicles, think of them as little bubbles, kind of carrying those proteins to wherever that protein is supposed to go. Maybe the protein is defective.

Maybe it didn't fold correctly and we have to get rid of it. Then it'll send it somewhere to be degraded. So here's the Golgi apparatus. proteins come in from the er and then they're modified and then they get sent out in these little vesicles to whatever their final destination is so another really important organelle here is the lysosome the lysosome um is basically where i call it like the cleanup crew the cleanup station of the cell dead parts of organelles dead organelles, dead proteins, things that have to be broken down, even like if there's a bacteria in there, pieces of bacteria in there, it's kind of like the trash cleanup system. Inside of a lysosome, and remember this is a membrane-bound organelle, which is really important and I'll explain why in a moment, inside of the lysosome there are digestive enzymes, meaning enzymes that break things down.

So they'll break things down. kind of like break down any trash and get rid of that trash and kind of send it out of the cell. And so it's really important that lysosomes have that membrane around it because what happens if it didn't?

The digestive enzymes would basically leak out and they would start breaking down and basically killing all the parts of the cell and the cell would end up dying. Okay. The mitochondria is another important one. Just like the nucleus, the mitochondria also has a double membrane surrounding it.

It contains these folds on the inside, which we'll look at in a second, called cristae. And in the middle of the mitochondria, there is a fluid portion called the matrix. We sometimes call that the mitochondrial matrix or the matrix of the mitochondria.

And the function of the mitochondria is ATP production, or in other words, cellular respiration. So it makes energy for the cell. So this is what that mitochondria looks like. So you could see these little folded parts, these zigzag parts that are kind of sticking out here. That's the cristae.

And then in the middle is the matrix. And again, there's the outer membrane and the inner membrane. So you can see those two layers of the membrane of the mitochondria. Another organelle that some eukaryotic organisms or eukaryotic cells have is chloroplasts.

Chloroplasts are where photosynthesis occurs. And there's like these flattened membranes that make it up. And those are called thylakoids. And within that flattened material, that's where chlorophyll is. Those are the pigments.

And so this is what that looks like. So here we have the thylakoids, kind of like these folded. things right here and then there's chlorophyll inside there okay the last organelle we want to talk about are peroxisomes now peroxisomes are kind of similar to lysosomes but they're different because they destroy hydrogen peroxide specifically so hydrogen peroxide which is here symbolized as h202 we don't really think of it as a bad thing right we can use hydrogen peroxide as like an antiseptic it kills things right it's helpful for us however hydrogen peroxide is toxic to the cells themselves so we have organelles called peroxisomes again membrane-bound organelles called peroxisomes that can actually break down hydrogen peroxide therefore detoxifying it and protecting the cell so it's kind of similar to lysosomes but peroxisomes are specific to destroying hydrogen peroxide.

Now, the last thing we're going to discuss is this theory, this concept called the endosymbiotic theory. And this basically is a theory that explains how eukaryotes basically evolved. Because back in the day, millions, millions of years ago, we all started with the same... prokaryotic organism. These tiny prokaryotic organisms.

So there were no eukaryotes back in the day. So how did eukaryotes develop? So what happened is, this is what the endosymbiotic theory states, is that larger prokaryotic or larger bacterial cells engulfed or ate up smaller bacterial cells. And those smaller bacterial cells ended up becoming the organelles.

of that big bacterial cell and this was the development of the first ever eukaryotic cells and so there are two major examples that prove the endo symbiotic theory chloroplasts and mitochondria these are two organelles that we just learned about and when we know about in eukaryotic cells that were actually their own organism so chloroplasts was its own bacterial cell mitochondria was its own bacterial organism on its own but they were engulfed by a larger bacterial cells and they ended up having the symbiotic relationship with the bigger cell so the bigger cell provided them with shelter with protection and they in turn provided the cell with energy so they ended up having this symbiotic relationship and this is how eukaryotes were originated and evolved. So really really early on we all came from the same early organism and then we had different types of bacteria right? We had larger bacteria and we had smaller bacteria.

So you can see that the larger bacteria ate up the smaller bacteria. and the smaller bacteria became an organelle that provided energy for it. So this is the evolution and development of the eukaryotic cell.

Transcript for:Understanding Cell Structure and Functions

Transcript for:
Understanding Cell Structure and Functions