Cell Organelles - Explained in a way that finally makes sense!

In this video, we're learning the parts of the cell. Now, I remember first learning this stuff and memorizing each organelle and a little description of what that organelle does, but I never understood the big picture of how these things work together to help the cell accomplish its functions. And that meant that my understanding of the cell and my ability to recall this information, let's say on a test, was pretty limited. So what I wanna do in this video is tell the story of protein synthesis, or the making of proteins, as well as a few other cell functions, so that whenever you learn each organelle and what it does, you're gonna understand how it all relates together and the different processes that the cell has to do. You're gonna understand the cell way better than you ever have. Let's jump to whiteboard and get started. The first thing I wanna talk about is the cell membrane. So our cells are these, kind of these little bags of fluid, and like any bag, it's gotta have some surface around it to keep all of that fluid in, and that's our cell membrane. If we zoom in on the cell membrane, it's gonna look something like this. Now, don't click off the video being like, oh my gosh, this looks super complex. The main thing I wanna point out with this is that most of the cell membrane is made up of this phospholipid bilayer. In red, we have phosphate molecules, and in the yellow right there, yellow-orange, is gonna be lipids. So these are phospholipids, and it's a bilayer. There's two layers of them, and this is gonna be the membrane that keeps all the fluid in. Now, if you look at this, there's a bunch of other stuff embedded into it, and these are all gonna be proteins. We have a protein here, we've got a channel protein that can allow certain things to pass in and out. Lots of proteins in here, but the main thing, this is a phospholipid bilayer membrane that's keeping all the stuff in. If this membrane ever ruptures or breaks, all the fluid and all the stuff of the cell would leave, and that cell would no longer be able to carry out its cell functions, it would die. Now, the stuff inside the cell we call cytoplasm. That term cytoplasm, cyto just means cell, and plasm just means fluid. So cytoplasm is the cell fluid. The next organelles we'll look at, we're gonna look specifically at this process of synthesizing or making of proteins. Synthesis means that you take multiple things and put them together in some new form. That's kind of what we do with proteins. We take amino acids and put them together to form a new protein. So let's take a look at some organelles that are involved in this process. The first one we're gonna look at is the nucleus. So the nucleus, most cells are gonna have one nucleus, and the nucleus itself has its own membrane. We call the nuclear membrane or the nuclear envelope, and inside of that nucleus is chromatin. Now, you may think of chromosomes. Aren't there chromosomes in the nucleus? Well, most of the cell's life, it's gonna be chromatin, which is these kind of long, curvy strands of DNA. It's only when the cell divides that that chromatin forms into chromosomes, but most of the time, it's in the form of chromatin. This is your DNA or genetic material, and that's gonna be inside the nucleus. So what does that DNA actually do? Well, in the nucleus, the DNA gets transcribed into mRNA. Transcribed just means to take something and make an almost exact copy of it. Now, if you already know about transcripts, you know that it's not an exact copy. It's making a copy of the opposite nucleotides, but for the purposes here, just think about it as an exact copy of a section of the DNA, and this mRNA is gonna code for a protein. Basically, each mRNA is gonna be instructions for one protein molecule. So in the nucleus, we convert DNA into messenger RNA or mRNA. Next, we have something called a ribosome. The ribosomes are super small, and they're spread throughout the cell. I've got them drawn in two clusters right here, but they're really spread out more than that in the cell. What's gonna happen is that mRNA is gonna travel to the ribosome, and the ribosome is gonna read the mRNA instructions and use those instructions to build a protein. Now, here's my favorite metaphor for this. It's building Legos. I've got a Lego R2-D2 in the background right here that you may or may not have noticed. Whenever I built that, I had to read instructions, and the instructions told me which bricks to combine in which order in order to make R2-D2. In this metaphor, the mRNA is my instruction booklet telling me what to do. I'm the ribosome, because I'm building the protein, which is the finished Lego structure, and each Lego brick is an amino acid. When you combine the amino acids together in the right way, they form a whole protein, and that whole process is taking place in the ribosome. Here is the ribosome. It's reading the mRNA, so the mRNA is feeding through the ribosome right there, and for every three nucleotides that it reads on the ribosome, it's gonna add in one amino acid. So right here, it's gonna be building out this long chain of amino acids forming a protein, each amino acid being one of those kind of orange circles right there. So our created protein at this stage is gonna be a long strand of amino acids. Now, it's gonna undergo some other changes before it's ready to actually do anything in the cell, but that's the point that we're at right now once we're done in the ribosome. So our nucleus contains our genetic information, which is gonna get transcribed into RNA in the nucleus. mRNA is gonna travel to the ribosome where our ribosome will read it, and then use those instructions to build a protein from amino acids. Now, where do these ribosomes come from? Well, we've got a lot of ribosomes, and we have a special structure that's gonna make those ribosomes, and that special structure is the nucleolus. So the nucleolus lives in the nucleus, but its job is to make the ribosome. It's basically a little ribosome factory. All right, where do our proteins go next after they've been created in the ribosomes? Well, we have another structure here called the rough endoplasmic reticulum, and the rough endoplasmic reticulum is gonna be dotted with more ribosomes. All throughout the ER, there are gonna be ribosomes, and that's why we call it the rough endoplasmic reticulum. When you look at a cell in the microscope, the ER, the rough ER, looks rough because it's got all these dots on it, which are the ribosomes. The main thing that the rough endoplasmic reticulum does is it's gonna be modifying the protein. At some point, the protein got made in a ribosome, and it passes through each of these layers, and as it does, it's gonna get modified by the rough ER. Now, when we say modified, what do we mean? I've got a list of four modifications I wanna talk about. One is it'll do the initial folding of the protein. So at this point, we've got this long strand of amino acids, which is our protein, but the actual proteins aren't just a long strand, most of them. They're gonna be different kind of three-dimensional structures. They could be a channel in the membrane that allows stuff to pass through. It could be a receptor on the outside of the cell membrane. It could be an enzyme that binds with a molecule and breaks it apart. It's gotta have a 3D structure, and we get that 3D structure by folding the protein. Rough ER can also do quality control, and so if it discovers a protein that's different than it's supposed to be, the rough ER can destroy that protein. It can also do something called glycosylation, which is a fancy term that just means adding a glucose or adding a sugar. That glyco just means sugar, and so a lot of our proteins are gonna have other things added onto them. So glycosylation or the adding of sugar, that'll happen in the rough ER. We can also do destination tagging. So the rough ER can tag the protein molecule with another piece that's gonna tell the rest of the cell where this protein needs to go. So is this a protein that needs to end up on the cell membrane? Is this a protein that needs to end up in some other organelle in the cell? Or is this a protein that needs to leave the cell in order to go bind with a structure on some other cell in the body? In other words, is it a hormone? So these are four modifications that can happen in the rough ER. The big thing to remember here is that the rough endoplasmic reticulum is gonna be modifying these proteins, getting the proteins ready to go out and do their function. What's next? After it goes through the rough ER, it's gonna be packaged and sent to the Golgi apparatus. It's got two sides to it. It has the cis side and the trans side. And that protein, which has been made by the ribosome and then passes through the rough endoplasmic reticulum, it's gonna pass through the cis end and then out the trans end. What the Golgi apparatus is gonna do is it can do further modifications. So if there's any extra modifications that need to happen before it leaves the cell, it can do that. And it's also gonna package it in a vesicle so they can send it to wherever it needs to go. So the Golgi is going to modify and package that protein and send it out to wherever it needs to go. It's kind of the FedEx or the UPS of the cell. Now, where are all the places that it can go? For one, it can be sent to the cell membrane because we have all these membrane proteins. If you remember this diagram from earlier, we've got all these proteins in the cell, like this channel protein that can allow certain molecules to pass in and out of the cell. Another place that the Golgi can send a protein is actually outside of the cell. So it'll package it in a vesicle. We've got an example vesicle right here. The vesicle's gonna travel to the membrane and kind of form up with the membrane like this through the process of exocytosis and send those proteins outside of the cell to go do some function. Or it could send them to some other organelle within the cell. Now, there's a lot of different places it can go in the cell. The one I wanna talk about, though, is the smooth endoplasmic reticulum. One big difference to remember about the smooth, obviously, is it's not rough, so it doesn't have ribosomes on it. But not only that, its function is very different. Whereas the rough ER was focused on modifying the proteins, the smooth ER is gonna be making or synthesizing lipids and carbohydrates. Now, wait, wait, wait, wait. We just said we send proteins to the smooth ER. What does that have to do with making sugars and carbohydrates? Well, if you think about proteins, what are proteins? They can do a lot of different functions. One of those functions is to be an enzyme. An enzyme is going to facilitate a chemical reaction. And whenever we're making a new chemical, such as synthesizing a lipid, well, we have to have enzymes to actually facilitate those chemical reactions. So we have special proteins that are made, sent to the smooth ER, so that they can work to make those lipids and carbs that we need. So even though way back at the beginning of this process, we have instructions from the nucleus on how to make different proteins, but really those instructions on making those proteins will also influence what lipids and carbs we're able to make. So it all comes back to that DNA. All right, let's do a quick recap of this process. So the nucleus contains our genetic material, our DNA, which is going to get transcribed from DNA into mRNA. The mRNA will travel to the ribosomes, which are made by the nucleolus. The ribosomes are going to translate the mRNA, read those instructions, and assemble a protein out of amino acids. The protein will travel through the rough endoplasmic reticulum. As it works through those layers, it's going to get modified in different ways. That'll be sent to the Golgi apparatus and get packaged where it will travel to wherever it needs to go. That could be to the cell membrane, it could be outside of the cell, or it could be to another organelle, such as the smooth endoplasmic reticulum, whose job it is to synthesize lipids and carbohydrates for the body. Next, we're going to look at converting food energy into ATP. Now, this may be the one organelle that you already know from seeing memes online and things like that, and that's going to be the mitochondria. You probably learned it as the powerhouse of the cell. So the mitochondria are going to be producing energy, but nothing can produce energy out of thin air, right? It can't be created or destroyed. And so we have to be converting it from one form to another. How do we bring energy into our body? Well, all of this is governed by this reaction. So we have sugar right here. Basically, we've got food that we're bringing into our body, and we have oxygen that we're breathing in. We're going to take both of those chemicals and put them through the process of cellular respiration, and we're going to be converting that into the things that we get rid of, such as carbon dioxide that we breathe out, as well as water. The big thing right here that we're doing is we're producing ATP. So we're taking these kind of higher energy molecules, we're going to break them apart, and then reform them into these lower energy molecules, which will release some energy, and that energy that gets released, we're using that to produce ATP, which is a usable form of energy. Our cells, the pumps and channels and stuff in our cells can use ATP to power all the different functions that we have in the cell. And that whole chemical reaction is taking place in the mitochondria. Fun fact about the mitochondria, the mitochondria have their own DNA, which is different than the DNA that is contained inside of your nucleus. And all of your mitochondria you got from your biological mother, none of it from your biological father, which is different than the DNA in your nucleus, which is a combination of your biological father and biological mother's DNA. Mitochondria are pretty wild. All right, let's go on to the next function. That next function is going to be the storage and breaking down of chemicals. We've got three organelles that are all kind of similar here. They're gonna be involved in these different processes. The first one is a lysosome. That prefix lyse, or sometimes light, like cytolytic, lyse just means to cut something open or to break it apart. So a lysosome is gonna contain a bunch of enzymes that we can use to break down different molecules that enter the body. This could be a pathogen that's entered into the cell and the lysosome will spill out its contents in order to break that thing down. It could be an old organelle that we no longer need that we're gonna use a lysosome to break it down. Or sometimes we'll go through the process of apoptosis, which is where a cell decides to destroy itself and so it'll use its own lysosomes to destroy itself. An example of that would be like an infected cell that doesn't want the infection to spread so that cell will break itself down. Now, those enzymes in the lysosome, where do those come from? Well, remember, enzymes are proteins. So these were proteins that were made by the ribosomes, which were coded for in the DNA of the nucleus, which then passed through the ER and the Golgi apparatus and then ended up in the lysosome. So it's even the lysosome, the proteins in there are connected, that process we looked at at the beginning of the video. Next, we have something called a peroxisome. A peroxisome is kind of like a lysosome, but instead of breaking things down, it's gonna work to oxidize or to neutralize some toxic substances. A big example of that is hydrogen peroxide, which is where it gets its name from. To remember this, just think perox and detox. It'll detoxify certain chemicals that end up in our cells. And then finally, we have the vacuole. The vacuole is just gonna be for storage of different chemicals. Plant cells have giant vacuoles that fill up a majority of the space inside the cell. Animal cells, like those in our bodies, have small vacuoles for just small amounts of storage. But certain cells, like fat cells in our body, will have larger vacuoles because they're gonna be storing fat molecules. But then a lot of other cells will just have small vacuoles inside. So vacuoles are for storage. The next process we're gonna look at is the process of reproduction, which is really gonna be either mitosis or meiosis. I say meiosis, some other people say meiosis. If I'm saying it wrong, just let me know in the comments. I know somebody will. Now I've grayed out a bunch of organelles in the diagram, the ones that aren't quite as involved in this process. But the ones that are heavily involved in the process include the nucleus, of course, because the nucleus has the genetic information and both copies of the cell during mitosis need a copy of that genetic information. I've got the cell membrane here still because both new cells are gonna have each their own cell membrane, and so that cell membrane has to kind of divide and pinch off into two new cells. And there's one organelle that we need to add, which is the centrosome. The centrosome looks like this, and it's actually gonna be two parts to it. It's gonna be two centrioles. So right here we have one centriole, and then another centriole kind of organized at a 90 degree angle to it. And what the centrosome is gonna do is it's gonna grab onto the genetic material, the chromatin, which will become chromosomes during mitosis, and pull those apart. So let's take a look real quick at what that process looks like. So here we have the chromatin, and during mitosis it's gonna separate out into chromosomes, which look more like this. And our cell's centrosome is gonna make a copy of itself. So we'll have two centrosomes now, and those are gonna form one at one end and another at the other end. And they'll use these fibers to grab onto the chromosomes and pull them apart so that each new cell is gonna have its own copy of the chromosomes. And here we have those two new daughter cells that each have a copy of the genetic material. That's how cells make an exact copy of themselves. Of course, we also have this process of meiosis, which is how our bodies create sperm cells and egg cells, each of which are gonna have just a half of the chromosomes. But again, the centrosomes will line up on either side of the cell. They're not drawn in that diagram, but they're gonna pull the chromosomes apart. And again, involved in that process are the centrosomes as well as the DNA or the chromatin in the nucleus and the cell membrane. Okay, our next function that we're gonna look at is the function of structure and movement. So the first one I want to talk about gives it its structure, and that's the cytoskeleton. Again, cyto just means cell, so this is the skeleton of the cell. And it's made of two main parts. It has microtubules as well as filaments. The microtubules look like this. They're these long, thin fibers that are gonna originate from the centrosome right here, and they're gonna connect all the organelles together. So these organelles aren't just kind of like free-floating and wandering around the cell. They're held in place by these microtubules, and those microtubules are made of proteins. So that'll give the cell its main structure, and then on the outside of the cell we have something called filaments. Now, there's really two types of filaments here. There's intermediate filaments, which are gonna be more kind of close to the microtubules, and then we'll have microfilaments, which are gonna be more on the outside of the cell against the cell membrane. I kind of simplified it here and just called those the filaments. So we have the microtubules holding things in place, and then we have the filaments around the outside of the cell providing some more structure. Let's add a few more things to our cell here. Some cells have structures called microvilli. The microvilli are just gonna be these foldings on the cell membrane. The purpose of microvilli is gonna be to increase the surface area of a cell. So not all cells have these, but an example of them is the cells in your small intestine. Your small intestine has to absorb molecules that you eat, and so we need a bigger surface area so we can absorb more molecules. So those cells are gonna have microvilli. Another structure on the outside of the cell is cilia. The big difference between cilia and microvilli is that they contain microtubules inside of them. At the base of them, there's gonna be something called a basal body, which is basically a centriole, and what these microtubules inside the cilia are gonna be able to do is allow the cilia to have some movement. So they're gonna wave back and forth so the cilia can move mucus around and move air around and different things. We find cilia in places like our lungs, like the bronchioles in our lungs. One more movement-related structure I wanna talk about here is a flagellum. A flagellum is basically the same thing as cilia, but rather than having a bunch of cilia, it's just gonna be one projection, but it's also gonna be filled with these microtubules. The only human cell that has a flagellum is a sperm cell, and so those microtubules in there are gonna have kind of a rotary motion like this, which is gonna propel the cell to where it needs to go. All right, we've covered a lot of stuff in this video. I wanna give you a chance right now to practice all of this stuff. So pause the video, see if you can name all the structures on this part of the diagram. And here are those structures back. And now let's take all of those away and let's go back to our diagram before this. See if you can name all the structures in this diagram. And even better, see if you can explain the process of protein synthesis in terms of all of these different organelles. And then here are all those organelles back, so you can check and see what you remembered. If you're learning all this stuff for a class, the only way to learn it all is to practice it and to make sure that you're using the best strategies to practice, I have a free A&P survival guide. Link in the description for that. It'll just give you a bunch of strategies for how to learn A&P and make sure that information sticks with you. I've also got some other resources, such as A&P study cards, including blank versions of the diagram in this video. I have other comprehensive unit guides that can help you if you're studying like the nervous system, digestive system, et cetera. Link's in the description for all of that. Special thanks to my patrons on Patreon, as well as my YouTube channel members. Thank you so much for your support of the channel. I really appreciate it. Hey, thanks again for watching this video and learning about the cell. Hopefully, you understand the cell better than you ever have. Here's another video that you might find helpful. Thanks again for watching. I'll see you in the next video. Bye-bye.