Dr. Benjamin Bikman | Basics of Biology | Lecture 1 (Official)

0:00 What does it mean for something to be alive? Is a cell alive? Is a virus alive or a seed? Biology encompasses all of that. This course is really a study of life. We're seeking to understand the complex interactions that make life possible. I chose to cover the most essential and most important parts of biology. I want you to understand the cellular components that give life to every animal and plant on the planet. We get into a surprising amount in just a handful of hours. The genotype that's basically like the blueprints and then the phenotype is the physical manifestation of that blueprint. We talk through the inner workings of the cell, the central dogma, what goes into a cell dividing. And then

0:46 lastly is cellular metabolism. You have gone from students to modest masters of biology. Anyone who just simply wants to understand biology, this will be a class that's interesting to them. Now you have a greater understanding of life, what life is made up of, and also how living organisms function. By learning this, my hope is that you will have a greater appreciation not only for your body, but for life all around you. Hello and thank you so much for joining me. I am Professor Ben Bickman. Today the material that we are covering is biology and I've entitled this course basics of biology because biology is a course that is is is a topic that is so

1:32 substantial that is so broad and deep that we would need an enormous amount of time in order to get through all of it. So in the time that we have together what I want to cover are the basics the fundamental pieces that go into biology. But before we go too far, let's take a moment and understand what biology is. Biology, as a scientist, I define it as the study of life and living organisms. And within that definition is this inherent understanding that there is an investigation. And there are cell biologists, actual biological scientists like me, where we are understanding, we're seeking to understand the complex interactions that make life possible at whatever level it is that we're

2:18 studying. Whether we are starting at the cell which is the most fundamental unit of life or whether it's the unit of the or the level of the cells coming together to form a tissue or whether it is the tissue working within a physiological system or whether it's the entire organism. Biology encompasses all of that. Now the first thing we're going to get into then is actually starting at that base unit of the cell. But in the time that we have together, we're going to cover four fundamental aspects or basics in biology. The first course or lecture that we're going to go through is the cell itself. So by the end of this immediate lecture, you're going to understand the cell, the nature of the cell, what it is, what how how do we define the life and the growth of the

3:03 cell. Next, the second topic or of of the basics we'll cover is central dogma. This is this grand idea that explains how we go from a genetic piece of information in the DNA through how that genetic information flows through this process that actually gives life to an organism and makes us who we are. The third of the basics that we're going to cover is cell cycle. The living and even the dying of the cell. How a cell will grow, how it will divide. And this is what makes us have the organism that we call our bodies. And then last, and I confess my favorite topic, is the energy within a cell. How does a cell get energy? After all, it needs energy. Like a

3:49 locomotion, like an automobile that needs some kind of fuel to move it, the cell needs fuel to give it its life and its work, its ability to get something done. All right. So, this first lecture, I have a few um key learning outcomes that I'm going to want to get through with you. The first thing at by the end of this lecture I want to make sure that you are capable of describing the aspects of cell theory. Second I want you to appreciate the different families of life at a cellular level. The difference between procariots and ukareots. And then third I want you to understand the cellular compartments or the components that make up the cells that um give life to every animal and plant um on the planet. And then fourth

4:35 and final within this general topic of the cell, I want to make sure that you have an appreciation for osmosis, diffusion, and gradients because these are central aspects that enable a cell that not only define the cell, but enable it to actually do stuff to get work done. Now, firstly, before we go too far, let's just pause for a moment. Again, I've already said that one time, but let's define life. What does it mean for something to be alive? Think about the the room you're in, the space that you're in right now. Look around and consider of the things that I'm seeing. What is alive? For example, is a cell alive? Is a virus alive? Is an animal alive or a seed alive? Think about these

5:21 things. We're going to revisit some of these in just a moment. But because I'm a scientist, I want some criteria. I want some list of things that we could go through and check and say if all of these criteria are met, then we can answer yes or no depending on whatever the item is that we're trying to determine whether it's alive or not. So, let's go through seven specific criteria that will that you could use to define or or to determine whether something is actually living. First of all, does it have some aspect of a cell to it? For something to be alive, it must have at least one cell. So, one or more cells is going to be the first of the criteria to define whether something is living. Second, does it have some aspect of metabolism?

6:08 Is there some need? Is there an ability within this thing that we're trying to determine whether it's alive or not to take in energy, to metabolize, to transform that molecule, that energy molecule into something that the cell can use to get some work done? And then can it eliminate wastes? That's after all a very important part of metabolism. Third, the third of the seven criteria, is it capable of growing and developing? Does it follow some kind of genetic instruction for growth and have a programmed process for determining that growth? When is it time to grow? When is it not time to grow? And then fourth, is it capable of reproduction? Can it make new versions of itself? That is an an essential aspect of whether something is

6:54 living. Everything that is living is determined to reproduce indeed to the point that that is an essential criterion. Fifth, is it capable of adapting? Um and this is by that I mean is it capable of evolving in response to its environment? Can it sense the environment and then start to adapt in order to ensure its own survival? Because after all everything that is alive wants to live and adaptation is essential is an essential component to that. Related to that one the sixth is is determining whether this thing is capable of responding to stimuli if something happens around it. Is it capable of determining this and responding and that would be of course lead to the adaptation over time. And then the final

7:41 component and this is really high level but so important is homeostasis. So if something is alive it must be able to in response to the stimuli have this ability to change some aspect of itself in order to maintain an an internal um constancy. It wants to maintain its current function. That is homeostasis. Now, homeostasis is a little bit of an ambiguous point or it can be a little difficult to understand. So, I want to take a moment and define it a little further. >> You starting your own college? >> Yeah. Well, it's well started. The progressives hope for universal education at something approximating zero cost. That's what we've got. We can bring you the best lectures that you will be able to get anywhere in terms of

8:26 their quality of content and also the production values. All the people we're bringing on board are existential philosophers in some real sense. We think that a humanities education should enrich your experience in every direction and be nothing but positive. Well, except also difficult and challenging, but that's also positive. >> Yeah, we certainly didn't have that when I was a kid. >> Just think about it at the level of the human body. We know we are alive. We meet all of these criteria. The human human body does. So, how does a human body respond to changes in temperature? If an environment is cold or if it's hot, you get into a hot uh into a let's say a cold bath. Everyone loves to cold

9:12 plunge these days. It's so popular. You get into that cold bath, that may be substantially lower temperature than you. If your body matched that temperature, you would die. So, you must have an ability to keep your body back at a normal range, at a normal temperature. Um, similarly, I am currently now filming this in Florida, but I'm coming from the mountains of Utah. That is a substantial change in elevation. Um, especially going from Florida to Utah where the oxygen is relatively more modest in the atmosphere, the body makes certain adaptations in order to get all of the oxygen it needs from a relatively thinner environment atmospherically. So homeostasis is that essential process of maintaining the the living thing being able to maintain an internal constancy

9:59 or keep itself constant. Now an obvious example of this around us or in our daily living an obvious example of homeostasis would be our home having a thermostat. The thermostat is going is the most obvious or simplest example of of something that's trying to seek homeostasis. Now, I'm not suggesting the thermostat is alive, but rather the ther the thermostat provides a good metaphor where if the temperature within the room starts to get too cold, the thermostat will sense this and it will kick on the furnace, thereby bringing the temperature back up to where the thermostat wants it to be. In contrast, certainly here in the muggy, hot environment of Florida, if things start to get too hot, then the thermostat will

10:46 sense this departure from the norm and it will kick on the air conditioner. Then the air conditioner will seek to bring the temperature back down. So that's just an example, of course, of homeostasis. Now let's bring that example of the or the metaphor of the thermostat and then assume some aspect of it in the body or wonder how it could apply to something like the human body. I'd mentioned the cold bath earlier. If the body were immersed in this really really icy cold water, that temperature change would be lethal. And so the body has a mechanism to respond in order to maintain homeostasis or that thermos ther the the temperature set point. And that would be it's going to start to shiver. So shivering would be a mechanism as the temperature is starting to drop. Nope, let's snap it right back

11:31 up and maintain homeostasis. In contrast, if we are in a very warm environment, things are getting too hot. The best way for the body to cool down is to sweat. So we start to sweat and then the sweat begins to evaporate and evaporation will create a chilling effect on the skin thereby allowing the body to try to keep that temperature from climbing too high. One last metaphor would be imagining a conductor. I had the great fortune in my childhood to play in lots of bands and my mom was determined to have all of her children learn musical instruments. And boy, I fought it at the time, but I'm very grateful now, right? That's so stereotypical. But I remember looking at the conductor and I was a trumpet player and boy, the trumpets can get so loud. Well, if the trumpet section, if the brass section's getting too loud, the

12:18 the conductor will respond to that knowing ah things are getting a little too rowdy in the brass section. And so there may be some sign to turn the volume down. And so the brass section would quiet down and maybe he needs more of the woodwinds. And so there'd be some kind of gesture that would coordinate all of these processes to work together. All of the band members and all of their distinct sections would know what to do, whether to play faster or slower, louder or quieter based on what the conductor was telling them. The conductor seeking some set point or homeostasis. Now, let's revisit some of the examples I mentioned at the beginning when we were wondering how to define life keeping these seven criteria in mind. So, first of all, a cell. Is a cell alive? Well,

13:05 it obviously meets the first of the criteria, which is that it must be composed of at least one cell. One cell is one cell. And so, it meets that criteria. And in fact, it does meet all of them. It is capable of reproducing. It's capable of responding to its environment. It's capable of adapting, etc. So, a cell is alive. And then that's no surprise of course to then say as we expand on that cell or put a bunch of cells together whether it is an animal or whether it is a plant all of those things are going to be alive as well. Even let's start at the very base or the first evidence of a plant or the first instance of it which would be a seed. Is a seed alive? Thinking think about that for a moment. The seed is capable of reproducing. It is capable of

13:51 responding to its environment after all. If it's not planted or watered, it won't grow. Once it meets these certain criteria, then it will know once it has the proper environment, it can respond to that and grow accordingly. So yes, even a seed is considered alive. What about a virus? A virus seems to be alive, right? We sometimes think that it might be similar to a bacteria, which is its own little cell. And we'll define bacteria in just a moment. But in fact, a virus is not alive. It does not meet all of the criteria. They don't grow. They do not maintain a virus does not maintain homeostasis. It cannot reproduce on its own. The only reason we talk about viruses at all is because of their ability to get into a cell and hijack

14:38 the cell and the cell is alive. So in that sense, the virus seems to be alive, but on its own it is not. It is not a living thing. It does not meet the criteria. And this of course would be similar things like a rock. A rock is not alive. Um the walls are not alive. These are not things that are responding to their environment. They're not uh adapting. They don't have any kind of metabolic process. So at this point you should be fairly comfortable with understanding the criteria of what goes into determining whether something is alive. And with this let's transition to the next subtopic here which is the cell theory. Given that everything that is alive must be composed of at least one cell, the cell theory is a fundamental concept in biology that essentially articulates the

15:25 properties and significance of cells within every living organism. In other words, it's just emphasizing the relevance of the cell. And within this cell theory, there are three main principles. One, and this is redundant, that all living organisms must be composed of at least one cell. That's something we already discussed. The second aspect of cell theory is that cells are the smallest units of life. That if we get down to the most fundamental or basic aspect of life, we come to the cell and beyond that there's going no further. There's nothing more fundamental to life. There's no unit that is considered more basic or smaller than the cell. That's the second aspect. Again, the cells are the smallest units

16:10 of life. And then lastly, the third aspect of cell theory is that all cells, all new cells come from pre-existing cells. And that's the aspect of cell division and which is something we're going to talk about when we discuss the basics in in of mitosis and meiosis in the third of these lectures as we get through the basics in biology. Now, very briefly, I've mentioned within that cell theory, it's that all living organisms are composed of at least one cell. I've already alluded to this, but I really want to bring the point home that organismal function, so the the whole um whatever the unit of life we're looking at, a tissue or an animal, you know, or the human body, that the they are composed of very organized or specialized cells that have lumped

16:56 together to form tissues. For example, the kidney cells, those are very unique types of cells that have clumped that have grown together in a particular structure. The liver cells, those are cells that are all the same that have grown together, muscle cells, skin cells, etc., etc. So the organism functions at the level of the tissues which are then composed of cells. So to understand the organismal function, you have to understand the role of the specific cells that are involved. And cells do have very specific functions, whether it's something as unique as sperm. Um, and we'll talk all about the gametes or these germ cells, sperm and ova or eggs, whether it's the the cells of the kidney, which have an incredibly unique structure enable them to filter

17:43 out certain molecules and neurons and other cell types. Now, because the cell is the smallest unit of life, um, and the tissues are composed of those cells, they all must learn to work together. And that's another aspect of the cell theory. So at this point in the lecture so far, you should be able to understand or describe what it means for something to be alive, as well as appreciating and understanding the three basic aspects of cell theory and why they're important. With that information in mind, let's transition into uh into this next level of understanding life by breaking up the cells into two main families. The proarotes and the ukareotes. Now as a

18:29 little pneumonic or teaching device the ukariots are what you are made of. Now uh let's get into it then. So two categories procariats and ukariots within the procariat family. So all of this you could imagine through this this a theory of evolution emphasis on this theory. We don't exactly know how life started. We don't exactly know how humans came to be humans. The idea, the prevailing idea is that it is a theory of evolution that if we take all life, we could go backwards in time and then the tree of life would start to get narrower and narrower and narrower coming down to one singular point. Within that one singular point, if we then reverse direction and start going back up, we would immediately get into

19:14 two distinct families. And the first being procariots. Now the procariats are plural. There are two lines or two smaller family lines that fit within procariots. Bacteria, which you've all heard of and we'll discuss very briefly, and then the archa. Archa or is a type of procariat that most people don't really appreciate. And then lastly, we have the ukareotes. And again, the ukariots are we're focusing on the most throughout this series because that's what you are made of. And we want to know more about ourselves and the role of biology within the human body. Or at least I want you to. Now one interesting thing about the ukariat and we will dive into this in much more detail very soon. They are it the ukariat family is very unlike the procariats. Yes, they're both

20:01 alive. They both they both meet both families meet all of the criteria of life but the ukariots have this if you zoom in and I'm looking at a procariot it would just look like a a plain little sack. There's almost there's nothing really to identify in it. Um, however, with the ukariots, we see these very distinct sections, these organels as they're known, and we'll define them more in just a moment. But there's an interesting theory that I just wanted to teach you because it's just it is so fascinating, which is our ability or our effort to try to understand where did the ukariots come from? What was responsible for such a significant departure in these cells? Why do some cells have such a basic appearance and function and another cell type is much more complicated? This is the theory of

20:48 endo symbiosis. So the endo symbiotic theory again theory is that at some point a proarotic cell a proarot a very simple just big bubble with nothing really to identify it or make it unique. If we looked at it under a microscope, the procariot at some point in its development would have had some kind of invagination or some pulling in of the membrane itself. So we have the cell is surrounded by a membrane and then the membrane started to kind of collapse in on itself resulting in these little folds and grooves that became part of the nucleus and other organels that we'll discuss. But then at the same time, and this is really where the endo symbiosis comes into play. Endo meaning

21:34 it's taking it in. Symbiotic meaning it's two things working well together. This then is a proary a proarotic cell that pulled in a bacteria. And this bacterium then became the mitochondria or the energy producing parts of the cell. The mitochondria. Um and as we discuss later on in this series in the cellular energy part the chloroplasts which is kind of a unique plant version of a mitochondria. So the mitochondria represents a totally unique part of the of the ukareotic cell and and that idea the origin of how that came to be there with its own unique DNA is that this was a procaryot that engulfed another procariat and them finding hey we get

22:20 along really well together. This is a symbiotic relationship. Let's just keep this going. And thus, we gave birth or we have the birth of the ukareotic cell which makes up you. All right. Now, let's back up for just a moment. I'd mentioned the archa. And the archa are the most unknown and certainly worldwide the most um the smallest in in abundance. But the archa basically are these small little cells, single cell organisms that only live in environments where nothing else can live. In other words, even bacteria couldn't live here. And these are things uh where it is, for example, blisteringly hot in certain areas where you may have hot springs that are at temperatures where no other bacteria could live or it is areas where the salt content is so high like the

23:06 Dead Sea or the Great Salt Lake in Utah that is so salty that it would kill bacteria. But these archa are built, they're designed to survive in these very hostile environments. Now, bacteria of course is something we're much more familiar with and rightly so because if we look at all of the trillions of cells that make up our body and we have of our own body type cells about 30 trillion but for almost one to one for every one of our cells ukareotic animal cells there is a bacterium or one bacteria cell and the bacteria are everywhere. You certainly everyone has heard about the microbiome. That's a very popular topic nowadays. So our digestive tract is loaded with

23:51 bacteria but so too not only on the inside but even the outside. Our skin is covered in bacteria. Now lest you think that's a problem, it is a good thing. It's a healthy thing both outside and inside. Once upon a time there was an idea that the number of bacteria on on or in the human body was 10 times higher. And that idea has been really changed and challenged and we generally nowadays accept it as about a one to one. So about 30 trillion of us cells and then 30 trillion of them but certainly worked in to the normal physiology or the normal biology of the of the human animal. So we have bacteria everywhere unlike the archa which are only living in hostile environments. Bacteria are everywhere else on the

24:36 planet and on the animals and plants. Now, speaking of animals and plants, that gets us to the ukareotes. So, the ukareotes are the form of life that you most recognize. These are animals. These are plants. These are little things living in the pond. If you get a piece of scoop of pond water and you see little things moving around, those are all going to be ukariots. So, most of what you think of when you think of life are going to be ukareotic cells. Now, let's define I've been alluding to some of the differences between proariots and ukariots. Procaryiots are very simple cell structures. I've been using this kind of analogy of a bubble. We need to get no more complicated than that. There's no nucleus. There are none of these other components or compartments within the cell. If we looked at them under a microscope, we and really zoomed

25:23 in, it would look like it's just a small bubble. Now, there can be different shapes and sizes of it, but there'd be little substance to the to the center of it. In contrast, the ukareot is a much more complex cell structure. It has DNA which is rather than just floating around. The DNA floating around and we'll define DNA soon. The DNA is just floating around within the procariat. There's no nucleus to encapsulate it or envelope it. Within the ukariots, there's a well-defined nucleus that is protecting and and holding on to the DNA, keeping it very enclosed. There are also other organels that we would see surrounding or in some other part of the cell. All right. So at this point now you should be able to identify and understand some of the differences between proaryotic and ukareotic cells.

26:12 As I mentioned one of the key distinguishing features between them is the presence of what's called organels. So now let's talk about the organels. I want to make sure that you understand the various components of the of the ukareotic cell which we call the organels. It's almost as if within the human body we have distinct organs. Within the cell there are this kind of cellular microscopic version. There are different parts of it that are doing different things. The heart is doing something different from the liver which is different from the kidneys. So too the nucleus is has a different role than the mitochondria has which itself has a different role from the endopplasmic reticulum. And you'll know all about those in a moment. Now cells are little

26:57 factories. They have just like within a factory, the cell has some instructions or protocols, a list of orders of things to get done. It has tools that it needs to use in order to build machines within the cell. And then it has the machines itself, the things that are organizing and working to get the cell to do what it needs to do. It has an energy source. A factory needs some energy source to fuel all of the working or to power all the work. So too does a cell. It has some form of internal management of the energy, storing it or burning it. It also has a compartmentalization. In other words, it's all the distinct little sections that I've been talking about. Within a factory, there'd be some piece of machinery over here producing some component. That component may then

27:43 go to this other big production line or some other piece of machinery. And then lastly, everything is built on site. Just like a good factory that is capable of going from base product to finished product, the cell has the same capability. Now within the cell itself, and again remember we're talking about ukareotic cells, there are some distinct parts of this that I want to cover with you for just a moment or over the next few minutes. The nucleus, the mitochondria, the endopplasmic reticulum, the centrosome which is very important to a process later on, peroxome and the Golgi apparatus. Let's define each of these briefly. The nucleus is something we're going to be revisiting later because it is so important in the central dogma or the

28:28 movement of genetic information. The flow of this genetic information that ends up creating life as we know it and giving uh definition and uh unique qualities to each of us as humans. So the fun the function of the nucleus is to contain DNA and the DNA itself stores our genetic code and also within the nucleus we have the beginnings of the replication or the reproduction capability. Remember that was an essential quality of of life. The thing must be able to reproduce. So DNA gets transcribed into RNA and you will understand that process very soon. And that's a necessary step. this this central dogma or the movement of genetic information in this case quite literally from within the nucleus as a DNA genetic

29:15 code and then moving out. Now when we move out along the nucleus itself in addition the nucleus is more important than just holding on to DNA. One interesting part of the uh the anatomy of the nucleus is that it has these teeny little pores and the pores themselves are much too small for the DNA to get out which is good. It's small enough that it will only let out what can meet the physical constraints of such a small little pore and that's going to be the RNA as we discuss the central dogma in the next lecture among these basics. Now if we go out of the nucleus we get into the part of the cell that we can call the cytoplasm. The cytoplasm in incorporates two main components. It's not only the water that

30:02 is within the cell. A cell does have water. It's like a little water balloon. It is does have water. That's called cytool. But then it has all of the other organels that are nonnucleus. So everything that we're about to get into now, all the other components of the cell, all the other organels are part of what's called the cytoplasm. So as we've left the nucleus, we've now entered the cytoplasm. And within that is the swimming water of the cytool. But then there are all these other components collectively that constitute the cytoplasm. So the first of these in fact in order that we would bump into in this case if as we come right out of the nucleus the nucleus is surrounded by these kind of flattened squishy sacks and it is a little awkward

30:49 where imagine if we had a long tube and we started to press it together but as we were pressing it together it started to have these little folds. it was kind of folding in on itself that and then it was surrounding the nucleus. So we had this tube we start to compact it that is the endopplasmic reticulum. So the endopplasmic reticulum are these flattened um membrane wrapped or membrane bound membrane wrapped organels and again that surrounds the nucleus surrounding the nucleus on purpose um because it is a necessary part of taking the genetic information from the nucleus and it must pass through the ER. Now the ER itself has two parts even though it's all connected. It is all one connected tube or network, but it has a smooth

31:36 part of it itself and it has a rough part of itself and they do have different functions even though it's all part of the same compressed flattened kind of pancakey stacked structure. Uh it's all connected but they have two different parts. The smooth part um is involved in producing fats. It'll and we'll talk all about this in the cellular energy component. It is storing calcium and cells need calcium. Some need them very um importantly like muscle cells or nerve cells. They have this specialized version of the smooth ER that is basically just acting as these big calcium sacks. And also the smooth ER is very important in detoxification. There may be some molecules within the cell that the cell needs to get rid of or it needs to neutralize and the smooth

32:22 ER can help with that. Then the rough ER is, we call it rough because when you look at it under a microscope, it looks like it kind of has a fuzzy edge. It doesn't actually have a fuzzy edge. It's just covered with these little things called ribosomes. Now, let's talk about the ribosome for just a moment. We're going to revisit the ribosome when we talk about central dogma and the flow of genetic information. This is how we get from DNA to actual protein, which is the final product. The ribosome is an essential part of this. So the ribosome is lining the rough ER. It's in the perfect position to get this genetic information from RNA and then to start to turn it into what will become a protein. Adjacent next to the ER. So the ER is the compressed pancake stacked network

33:10 around the nucleus. Adjacent to the ER is something called the GGI apparatus. It is outside and around in distinct sections the ER because it's also part of moving things out. If something is originating from the nucleus and it's moving out on its way to get out of the cell, it then has to pass through the Ge. And the GG is going to be involved in some of what's called post-transational processing. Now, the word translation in the context of biology at the moment doesn't make a lot of sense, but it will very soon. But translation, suffice it to say, is just part of the movement of the genetic information from the nucleus on its way out of the cell. So it's essential in packaging things up to make it suitable for getting to the edge of the cell and

33:56 then coming out. Now, the most famous of the m of the organels is maybe second only to the nucleus. The nucleus is probably the most famous, but for a guy who studies energy like me as an obesity scientist, I focus mostly on the mitochondria. So the mitochondria is the next organel to talk about and that is the essential powerhouse of the cell. That's how we always learn about it in basic biology. It produces the main molecules of energy that enable the cell to get work done. So all energy is coming from the mitochondria and within the mitochondria are some essential components which we will really explore in the cellular energy topic. But this is things like the citrate or kreb cycle. It is also the electron transport

34:43 system, but all of these things are working in concert in order to produce energy for the cell. Then we have a couple other organels that are important, but we're not going to really explore their role in the in the basics of biology course. We have the lossome, which is another part of the cell that's essential for just cleaning things, but also is the peroxazome. The peroxome is similarly important in breaking down stuff, including some toxins and things like that. Now the last couple things I want to mention with regards to the organels or the structures within the ukareotic cells are important because they're very relevant to the upcoming processes of mitosis. Later on we're going to talk about how a cell grows and then divides which remember is an essential criterion of life. The

35:29 centrosome is an essential part of it. The centrosome are these little organels that start to orient themselves. They literally are moving through the cell in order to then start pulling the cell apart. It's almost like they have the similar charged like a magnetic pole wanting to push something apart or pull it apart. So the centrosome is essential in actually building or structuring out these things called filaments. And these little filaments are these kind of string like structures within a cell that not only give we'll talk more about them in just a moment actually because they're a part they're a formal part of the cell. But the microtubules are these threadlike structures that the centrosome is coordinating. So the centrosome is basically determining the orientation and then the eventual splitting and the directionality of the cell pulling apart. And then related to

36:17 this are things called the cytokeleton and the microfilaments. And these are the last parts of this that we'll talk about within animal cells. So the cytokeleton is actually this small little network. I'd mentioned these little threadlike molecules that give the cell its particular structure or shape. Not all cells are shaped the same. The cytokeleton just like the skeleton is giving a shape and structure to my body. The cytokeleton cyto meaning cell the cellular skeleton is giving shape and structure to the cell itself. And very related to that are these things called microfilaments. and a filament. Um, if if you haven't, make sure that you watch my fundamentals and physiology series and we talk a lot about muscle contraction. Within muscle

37:02 contraction, we have a lot of these filaments, but the filament is necessary for a cell to move. Whatever movement you're thinking of, whether it is in fact a muscle contracting, whether it is the sperm swimming, um, that is a movement that requires some degree of microfilaments. It's also important in the actual splitting apart of the cell. This process called cytochinesis which is the last step of mitosis which we'll talk all about. So the eventual the cells moving apart and it eventually pulls apart entirely. The microfilaments are going to be an important part of that process. Now one last thing then to discuss and I've alluded to it before or one last organel to mention is an organel that's unique primarily to plants. Now everything I've just been

37:48 describing is very relevant of course to animal cells but with plant cell we have one more which is kind of a unique plant version of the mitochondria which we will discuss in the cell energy topic but that is the chloroplast. So the chloroplast is the unique version a plant version of the mitochondria that's capable of getting energy from the sun rather than getting energy from food from calories like we think of when we eat um calories. That's what the mitochondria needs to burn to produce energy. The chloroplast, if you will, is burning the sunlight in order to create energetic molecules or food for us to then eat. All right. So, with all of this in mind, to wrap up this little subsection within the cell topic here, we let's just revisit the idea that the

38:33 cell is a little machine. With all of these things in mind, you'll recall that we'd mentioned that the cell as a as a little factory or this machinery. It has some instructions or protocols that it needs to follow. It has some tools that it needs to build machines and it has the machines themselves that are enabling the cell to do whatever it needs to do. And the machines can be quite specific. Muscle cells will have different machines than kidney cells for example. It must have an energy source and it must have an ability to manage the energy to know when to store it and how to store it to know when to burn it and at what degree to burn it. And then compartmentalization within the little organels themselves like a factory has different sections where different work is getting done. So too does the cell. And then it lastly has the ability to build everything it needs on site. It

39:18 doesn't need to offload any part of its work. All right. Up till now then with this little subsection behind us, you should be able to understand the various components of the cells. Now an important part of all of this and I've used this word membrane very often. So let's talk about cell membranes because this is an essential part of allowing a cell to survive. So at the end of this little topic, I want you to be able you should be able to detail or explain to a family member or friend the utility or the the usefulness of the cell membrane and the cell wall in general. And within that earlier example that I used of looking at the cell as a little factory, one of the final components of that was the ability of the cell to compartmentalize. Just like the factory

40:05 has different sections doing different work, all of which is seeking one overall level of productivity, the cell also has the ability to compartmentalize. Now, it doesn't have the benefit of having a distinct machine in one singular e section. It must be walled off. So, the compartment must have some physical structure dividing it. The factory doesn't need a fence to close it off, but somewhat like a fence, the cell must have the ability, some barrier. But the barrier must be functional. It can't just be totally walled off. Otherwise, it s serves no purpose. It must keep out some things but allow other things to come in. So with this idea of compartmentalization,

40:52 it allows us to subdivide the cell into distinct regions or compartments. And then these compartments are capable of doing whatever work they need to do and to do so separately yet complimentarily with other parts of it. Another aspect of the compartment is that these compartments is that they are called membranebound organels. By membrane bound it means that the the structure is enclosed within some membrane and that is the that is defining or giving um shape and and then purpose to whatever the organel or the structure it is that we're talking about. But as I mentioned it cannot be something that closes it off entirely. Otherwise the cell would have no purpose for it. So it must have

41:38 this aspect of permeability or a semi-p permeability. So it can't let everything through. If it if everything could come in and out, it serves no purpose. Similarly, if nothing can come in or out, it serves no purpose. It must be able to have the ability to discern. Okay, you are something I I need to pull in. In contrast, here is something I need to dump out, but you other thing you don't come into me. You're not supposed to come here. or if you do, I need to have a way to regulate what you do uh or how much of you is coming in. So the first thing that I want to explore with you is the actual cell membrane itself. So before we zoom in any further, let's just talk about the cell membrane. There actually a handful of names for this. What I'm calling the

42:25 cell membrane is also referred to sometimes as the plasma membrane. And then even more precise is something called the phospholipid billayer. And the phospholipid billayer is another word. It is synonymous with the cell membrane and plasma membrane. But it's helpful because it actually explains the composition of the membrane because if we zoomed in super super deep into the cell membrane, we would see that it is actually these two opposing layers of a type of fat called phospholipid. Now, we're going to talk about phosphoipids later, so we don't need to worry about their structure at the moment. But what is so essential about these is that they are what's called amphipathic. Amphipathic meaning that there is what's

43:12 called a hydrophilic side to it, which in this case is my wrist. Hydrophilic. And then there is these hydrophobic tails. In fact, technically it's two. It's like this. So imagine this phospholipid billayer which is creating the membrane of the cell. And the top part again is what I called is hydrophilic. And you can hear some words in there. One, you hear of course the word water or hydro. And then fillic means loving. So the top part, the head loves water, which is good because the body is mostly made of water. The same thing with cells. Most of what is our mass is water. Up to 60% of the human body is water out of the cell and in the cell. But we can't have it just freely

43:59 mingling other otherwise we'd just be a big blob of water and mess. So the phosphoipid billayer has a water loving section which is facing out to the water both the water outside the cell and the water inside the cell. But if it was just this phospholipid itself which is a type of fat that creates the membrane it it it has this of course hydrophobic tail to it or the tails. Well that can't face the watery side of the cell. the cytool. So it has another phosphoipid stacked at its bottom. So it has its two the tails which are hydrophobic who don't want the water are pushed in together. So they can both take a breath of relief and avoid the water. And then the hydrophilic heads are also enjoying

44:45 life because they're able to face the water both the water outside the cell and the water inside the cell giving rise to the term again amphipathic. So amphipathic describes molecules that have both hydrophilic the head and hydrophobic the tails parts of it. So water loving and water repelling parts. So that is the phospholipid billayer or the cell membrane that encompasses or encloses every single cell of the body. Every cell of the body has that phospholipid blayer identifying and giving shape and structure to itself. Now an alternative form in addition to the phosphoipid billayer of the cell membrane you can also in some instances get what is

45:30 called a misel. In my fundamentals of physiology lecture we talked a little bit about this but a mi cell is an important part of the movement of fats within the body. So when we're moving fats around in the body it's typically taking in the form of a mi cell. But in this case, it's this funny little structure whereas as opposed to having the phosphoipids against each other like this and then enclosing the cell, it's all of these phosphoipids stacked in a sphere. So imagine if we could just multiply all of my little awkwardly shaped phosphoipids here and start pinning them against each other, but keeping the phosphilic oh sorry hydrophobic tails together. So the hydrophobic tails are all facing inwards and then the hydrophilic heads

46:16 are all facing outwards giving us this small ball-shaped structure called a misel and that is again how fats move through the body. Now let's go back to the phospholipid billayer for a moment which is the cell membrane. So within the cell membrane we have these phospholipids that have two tails. Each of these tails is what's called a fatty acid or just a distinct fat. Now you've heard of these terms called saturated fat. You've heard of monounsaturated fat and you've heard of polyunsaturated fat. Now I don't want you to bring any bias to this part of the conversation. Don't be thinking any one is better than the other. Um there's a lot of I would say bad science that has gone into our understanding of of dietary fats. But we can classify fats chemically into those three areas. Saturated monounsaturated

47:05 mono being one unsaturated bond and then the poly. And it is all about the carbon bonds. So if we look at a fat, it is basically a long string of carbons bound together in this kind of zigzaggy chemical structure. Carbon, carbon, carbon, carbon, carbon. So all these carbons bound together. If it is a saturated fat, it is just a straight line of carbons. It's that simple. Every every bond is linked. In other words, fully saturated. However, if it's a monounsaturated fat, like the fat from olive oil, then it has one single carbonarbon bond that is not fully saturated. It has basically an empty spot. And that takes the linear straight saturated fat and introduces a

47:52 kink, but only one kink. But having that one kink does change. If you have the phospholipid, one is a straight saturated fat and the other has a little kink in it, it starts to change the degree to which it can stack up to other phospholipids. And so if we then look at the phosphoipid billayer of the cell if we it starts to change the fluidity or the rigidity of of the cell membrane. Now before I get into that in too much detail, let's just introduce the final the third and final fat which is polyunsaturated. As the name suggests, the polyunsaturated fat is going to have not only the one unsaturated bond that the monounsaturated has, but it can have another one or two. So, it can have two or three of these unsaturated bonds.

48:38 Now, the shape is even more bent. There are even more kinks in the shape of these fatty acid tails of the phosphoipid. And with all of that in mind, let's then put it in the context of the cell membrane. If you have phospholipids that are primarily um composed of saturated fats, they can stack together very nicely and tightly. However, if the cell consisted entirely of saturated fats within its phospholipid tails, it would be too rigid. It's too tightly packed. Now, the cell is too dense and it's not permeable enough. It can't be fluid and dynamic and it maybe can't even allow things in. It can't make room for anything to slip through. But remember, in order for

49:24 compartmentalization to work, it must be semi-permeable. It must have the ability to let some things in or out. So, if the cell membrane is composed of too much saturated fat, things get too rigid and too tight. Of course, in contrast, if the cell was only composed of very kinky fos uh polyunsaturated fats, these would be the types of fats that we get from seed oils like soybean oil or corn bean or corn oil, so-called vegetable oil. There's nothing vegetable about them that is totally a misnomer. They are more accurately simply defined as refined seed oils. In that case, with the multiple kinks, they're so kinky. They don't mesh together very well. If the if the phosphoipid billayer was composed of these multiple kinkedked

50:11 polyunsaturated fatty acid tails of the phosphoipid, it would be too loose. They're not close enough. Everything is too in fact indeed it would actually just burst apart. But it's too permeable. There wouldn't be enough structure to it. So thankfully the cell actually has the ability to regulate the composition of the fatty acids. enough saturated fat to give it some structure, but enough poly or monounsaturated fats in order to give it a little bit of dynamic aspect and fluidity. And again, because of all of this, not only the nature of the phospholipid billayer and its fatty acids, but also other components in the cell membrane, it allows the cell membrane to be semi-permeable. So some things can come out and some things can come in, but only some things and some things can go out. And a cell

50:58 can be specific to allowing some things to come in or out depending on the nature of the cell. Not all cells will have the same need for the same molecules. And because of this, embedded within the phospholipid billayer are other structures. So let's just discuss some of them for just a few minutes. So we have now adequately discussed the phospholipid billayer. But woven within or sprinkled within this phosphoipid billayer are other structures that allow some degree of interaction with other cells or other molecules. Firstly, it has the ability or the cell has on it transporters and we'll talk more about them in a moment. But a transporter is just as the name suggests. It allows molecules to move in or out that wouldn't otherwise be able to get

51:44 through the membrane. So this is a very structured way of controlling. It's like a a gatekeeper. Okay, I need some of you, but I only need two of you. So, two of you can come in now. No more can come in. That's what a transporter would do. Also embedded in the cell membrane could be an enzyme. So, a little protein structure that may be embedded on the inside or the inner side of the cell membrane and it can take one molecule and we'll talk about enzymes soon and change it into another molecule. Enzymes can be freely floating in the cytool, the watery part of the water balloon of the cell or in this case bound to a structure or bound to the membrane. Also on the other side of the cell could be a cell surface receptor. This is an essential aspect enabling a cell to

52:30 respond to any other signals that may be coming from another cell. Over the next few minutes, we're going to talk a little bit about glucose and insulin. And remember, I study diabetes as a scientist. So, this is an example I'm always quick to come to. On the outside of the cell, the cell may not know. The cell is going to be thinking, "Boy, I sure could use some glucose right now. I'd love to eat some blood sugar right now." But it needs to know, well, is there actually enough for me to take in? Is it my turn to take in some glucose? I don't want to starve everybody else. The cell wants to play well with other cells, but it needs to know whether it's time to pull in the glucose. So there would be a receptor on the surface of the cell that would sense for example the hormone insulin. So insulin would be would come and bind its receptor and that receptor itself is embedded within

53:18 the membrane in fact spanning the entire membrane. So across this phosphoipid billayer all through it would be this insulin receptor. So insulin comes and essentially knocks on the door of the cell and then the signal transmits transmits through this and then right next to it would actually be what I just mentioned which is an enzyme a membranebound enzyme and so it starts to send this signal within the cell and the ultimate effect actually to go back to the first structure I even mentioned now would be opening up a transporter. So then the transporter would open allowing the glucose to come in. And we're going to revisit that example more in a moment, but it's just an interesting way to bring all three of those into one thing. Now, other structures on the cell that are bound to the membrane also give it an identity. It's a way for the cell

54:04 to recognize itself. You of course are familiar with autoimmune diseases. Sometimes what goes wrong in an autoimmune disease is that immune cells fail to recognize other cells as part of itself. you know rather than looking at this and saying oh I recognize that signal on your membrane so I'm going to leave you alone it forgets or the cell doesn't have the right signal and so the immune cell will think ah you are foreign and I need to destroy you that is really the nature of an autoimmune disease and again that's based on some component that is embedded in the structure of the cell like a flag basically poking up and saying hey I'm on I'm on the same team and then other aspects a couple final ones are cell adhesion molecules. So on the surface of a cell there can be essentially the two

54:51 different components of Velcro which allow cells to bind together which is of course very important for every single organ in the body. What keeps the kidney uh all lumped together well it has this ability to adhere to itself. So cells almost all cells of the body need to be adhered in order to grow well. And so there are cellto cell adhesion molecules that lock things in place. All right. Now let's talk about going back to the membrane and its ability to be semi-permeable or to discern what should come in or what should go out. Let's just discuss briefly the aspects or the molecules that can pass. What can go in and what isn't. Well, there are some things that can go in very very readily. And these are small or nonpolar

55:38 molecules. Non-polar being that they don't have an electrical charge to them. They're neither positively charged nor negatively charged. They're neutral. So non-polar or again very very small or they can be lipid based or fat because like attracts like and I just got done describing the fact that the cell membrane the phospholipid lipid meaning fat the phospholipid blayer of the cell membrane is fat. So what encompasses every cell is primarily fat. And so if there is a fat coming, it has an easier time, not not always, not uh limitlessly, but it has an easier time simply moving through the membrane. It's basically saying, "Hey, I'm like you. You're a fat. I'm a fat. I can slip through." And this is why steroid hormones are able to get into a cell

56:24 very readily. Steroid hormones being not only of course the famous ones of the sex hormones, all estrogens and all androgens, the most famous androgen of course being testosterone, they're able to freely move through the cell membrane. They come to the membrane and say, "Hey fats, I'm also a fat. Let me through." And they're able to get through. But also water, water is very, very small and is able to generally pass through the cell membrane fairly well. But if a molecule is not only much much larger, but is charged, it has a charge to it, positive or negative. Now, it's going to have a very hard time getting through. It has to be regulated. So, this is going to be things like not only like a a glucose molecule, like a sugar um a sugar molecule will have some degree of regulation. It's simply too

57:10 big. But also electrolytes. So, things like sodium and potassium and chloride. Sodium and potassium having very positive charges, chloride having a very negative charge. These are molecules that are too polar or too charged to just slip through. They have to be regulated and they are through specific molecules that can open and close to let them through responsibly. Now, the last part about the cell membrane that I want to mention is just how important cholesterol is. We unfortunately live in a day and age when cholesterol is vilified. Indeed, most clinical practitioners focus more on cholesterol than probably any other aspect of a patient's health. They want to measure your blood and they want to look at your cholesterol levels usually so they can

57:57 put you on a cholesterol lowering medication. But this paradigm has really vilified an utterly essential part of just life at the level of every single cell. So, we don't even need to mention the steroid hormones that I just discussed. All steroid hormones, not only the sex hormones, but many, many more are all built on cholesterol as a base. So, the cell will take cholesterol in and then turn it into whatever that steroid hormone is going to be. Again, many more hormones than just the sex hormones. So, not only is cholesterol essential to that, but cholesterol is also embedded throughout the phospholipid blayer. It is essential for not only structuring other um structures or or giving shape and place to other

58:42 structures like the insulin receptor I mentioned earlier where you have this protein heavy receptor spanning the length of the phosphoipid billayer. It forms in areas where there is what's called a chole lipid raft which is this cholesterol-heavy area. So cholesterol is not only clumping around to tell receptors where to be located, but it also is an essential part of the dynamic fluidity of the cell membrane. It gets in the middle of some of these phosphoipids and say, "Hey, you're too you're too close. You're too tight." Mind you, even if it is with mono or polyunsaturated fatty tails, the cholesterol gets inserted just to give it um some more dynamic fluidity, enabling the cell to move and enabling some components to move around. So if we looked at the surface of a cell, if we

59:28 were standing on the surface of the cell and the cell was the size of the moon, we would see these components, these various structures that I talked about earlier, they're not just rigidly locked in place. They're flowing around. It's almost like we would be standing on an ocean and we would see something moving. So the cell is not a rigid set structure. As much as its shape is generally staying the same, within that shape is this readily moving these readily moving parts and cholesterol enables that to happen. So, thank goodness for cholesterol. Now, everything I've been describing so far is perfectly suitable for understanding animal cells. But within the ukareotic family of cells, less we forget, there's also plants. Plants are ukareotic. They meet every definition of life. In

1:00:16 talking about the dynamic phospholipid billayer of the animal cells that stands in stark contrast to the very rigid yet still semi-permeable walls of the plant cell. So the plant cell still meets all of these um the the necessity or the necessary aspects that allow the cell membrane to be permeable to selective things but it is also composed very heavily of a structure called cellulose. And so cellulose rather than the cell kind of being a blobby fluid thing the plant cell is very rigid much more rigid but still semi-p permeable because of the presence of cellulose wrapping it around. So rather than a phosphoipid blayer it has this cellulose heavy layer which makes the cell more tough. All

1:01:02 right. So by this point now within this subtopic you should be able to understand the utility or the beneficial role of the cell membrane and the cell wall in general.