Anatomy & Physiology 1 - Lecture 4 | Cell Structure & Function (Transport, Osmosis, & More)

This is my favorite lecture of the series. My students always think I'm a nerd when it comes to cells because they are the living units of your body. As a brief reminder, you have 30 trillion of these guys. And I want you to remember if you are doing something, it's because the cells of your body are doing it for you. Now, that being said, I want to remind you, uh, the cell is a level of organization pretty high up. As we've Been going through this course, we've talked about how atoms like ch, carbon, hydrogen, etc.

will bond together and form those molecules of like water, uh different carbon dioxide, oxygen, etc. And then we built some macroolelecules. We talked about those macroolelecules as the big molecules like the carbs, proteins, lipids, nucleic acids that we are made of. And then finally, we get to organel, which is a specific small organ inside of the cell. And I always star That one because that is where we're talking about now. So that means as a student, you cannot just forget everything we've learned below here because these guys literally build your cells. So just to remind

you, if we were to draw a cell, so I'm just going to draw a blockshaped cell here. Maybe this will be a liver cell. So we'll say this is a liver cell. I'm going to draw the outside in pink. Maybe draw the inside here in pink. Maybe have a lot of Endopplasmic reticulum here. Maybe some GGI apparatus kind of bracketed route here. And we've got a decent amount of mitochondria inside of the liver cell as well using a lot of energy. Now that being said, everything I drew in pink right now is actually a lipid.

It builds our membranes of our cells. Yes. So, the membranes of our cells and the organels within them will be made of lipids. And we'll talk specifically about the structure of this guy in a second. But Not only that, we know that liver cells also have our DNA inside the nucleus here. So, we have DNA, which is a type of nucleic acid. And we'll also be reading some mRNA transcripts we'll talk about later on that will be floating around inside of the cell. So, those are made of the nucleic acids. And then from there, oh

my goodness, I want to draw a bunch of these guys. We have a variety of different red looking structures that may look like this and this and maybe Something like this. It's my favorite one. And then maybe some inside like this. These are all going to be our protein. So proteins are going to be in red here. And then lastly, very sparingly, we will have some branches off potentially that look like this. and maybe a few especially inside liver cells that look like this. These are going to be some carbohydrates. So, I just don't want

you to miss the forest for the trees. Cells are made of Macroolelecules which are made from many, many atoms put together to form them. Now, as a reminder, do you remember from last class, are you what you eat? Are you what you eat? Yes, you are. Because all of these base units came from your food. you broke it down into the individual units and you put it back together inside of your cells to build your own. Now, that being said, you've probably looked at a general cell before and just been like, "Oh, yeah, it Has

all these membrane bound organels." Maybe you related it to a city as a biology uh class in high school, but I want you to remember really that not all cells look like this. In fact, if I were to draw a red blood cell, it'd be a lot smaller and it would literally just look like this. be a bic concave disc and there is no nucleus and there are also hardly any organels no organels inside the red blood cell. So this is a red blood cell. Now the red Blood cell is made of about 98% of

one protein called hemoglobin. So really the red blood cell is just a big packed full of hemoglobin protein and some enzymes that are also proteins. But then we can also look at like a neuron. And a nerve cell sometimes can look like this with a long branch goes all the way here. And it can actually be up to three feet long. And we can just be packed full. Here's the nucleus. Lot of mitochondria inside this nerve cell. Lot of proteins throughout this long branch called the axon. We also have other cells coming in and forming

some barriers. Uh, and there's other things inside of it. But I want you to notice like the differences. This one's super small, made of just protein. This one's really long, made of a lot of lipid and mitochondria. This one's got a basically a lot of stuff. Liver cells have most everything. But then there's also some like your lymphosytes, like Your white blood cells that the majority of the white blood cell, this lymphosy here, literally translating to the lymphatic system cell, the majority of this is actually a very large nucleus with a bunch of DNA. In

fact, so much DNA, it's like much more than the average cell so that it can make a variety of different proteins to help fight off a variety of different infections. So, all in all, are all cells structured the same way? Are all Cells structured the same way? No, of course not, because all these cells have different functions as you know from this course. So, don't just get focused in on, oh, a cell is just this like weird concept that we don't really know exactly what it is. No, they are the structure and function of your

body. These neurons are long so that we can send long signals, say from your spinal cord to your pinky toe to help you move your foot. Yes. Or maybe to feel Something that's on your pinky toe and send that information all the way up to your spinal cord and up to your brain so you can perceive it. Hey, these lymphosytes, they're really small. They've got a lot of DNA, a lot of information on how to build proteins, how to fight things off. And they're very mobile. They can move throughout. So they're kind of tiny and

malleable. They can bend and stretch. Whereas your liver cells, they've got to make a bunch Of proteins and they've got to store some stuff and so they've got a lot of different organels to do that. Red blood cells, they just got to carry oxygen and CO2. So all they need is the protein that helps them do that. So all in all, cells all have different structures, different functions. Awesome. So that being said, we do need to go through some main kind of structural implications and location specifically that are uh the same through all cells And

then the two main goals of any cell which we'll talk about cellular respiration a little bit which we already did in the previous video as well as protein synthesis. Then we're going to talk about the membrane, its importance, uh what it's structured like, what the voltage and how transport happens in and out. A lot of things are implicated by what comes in and out of cells. And then we'll talk about um some membrane proteins and osmosis. And then Hey, what could go wrong if some of these things were off? What could go wrong if the

fluid outside the cell is off? Should the cell just stay alive? Should it kill itself, etc. So, we're going to get through all of that today in this video. I hope you're looking forward to it because I certainly am. So, to get started, as a reminder, location, location, location. We really know need to know where things are located. So, first what I'm going to do Is obviously draw the blood. Okay? Because the blood's a river of life. Goes everywhere. We remember that. And anything that the cells need will be given to them by the bloodstream.

And so really the bloodstream when we get to the cellular level, it'll have little openings inside the blood vessels to help leak some components out of itself. And we'll talk a lot more about that in A&P2, but just know that whatever you put in your blood will bathe your cells. So I'm going to draw a cell here. Just any cell. We're going to draw pretty big because we're going to have some things inside of it going on. So, what types of things are going to be bathing the cells? Well, we know the blood is mostly

made of fluid called plasma. So, there's going to be a lot of water inside of it. And there's also going to be other nutrients and electrolytes, etc. So, I'm just going to say like water, electrolytes, we've Talked about those earlier like sodium, potassium, calcium, etc. Uh there's going to be some nutrients say like nucleic acids, etc. or sorry, um amino acids, etc. Um, so that being said, if there's components leaking out of the blood into this space, we now have a few different locations that we need to be aware of. So I need you to

jot these down. The first one obviously will be in the blood itself. That's location number one. Now, in terms of the blood, we Won't talk about an NP1, but the blood has a fluid-like component called plasma. It's a watery portion. And then we'll also have the cellular portion. So like if we had red blood cells in here, they'd be kind of be sitting around here like this. The cells themselves won't leak out, but the fluid will. So we're talking specifically about the blood plasma. But then as we leak out, we have a new space that's

outside of the cell, right? But it's not inside of the blood. This space is going to be called the interstitial space. Number two, the interstitial space. Interstitial. What does that mean? Inter means between. In stishell, I actually haven't looked up that prefix, but I'm assuming it's meaning between two other locations. So, like if you're stitching something together, right, it's going to be between one cloth to the next. Interstitial means between those two spaces. So, we've got The interstitial space or interstitial fluid. You may hear that as well. I'm not sure what your instructors are going

to call it. But then, most importantly, we have a fluid fil space inside the cell itself. So all the way throughout the cell we will have fluid called the cytoplasm or the cytool. That is going to be our third location and that is going to be the intracellular fluid or space. Okay. And that is inside the cell. So Intra means within. And so that is in a way the most important space because that's the stuff the cell can actually utilize. Now, how did we separate out these different spaces? Well, we have membranes. So, the blood

vessel will be lined with cells with membranes and then the cell itself will have a membrane and that's going to be called the phospholipid billayer. So, it's a phospho lipid billayer membrane. Okay. What what Is what does that mean? Right? I'm just saying that the membrane is a lipid and we know that lipids do not dissolve well in fluid. In fact, it makes a barrier between two fluid fil spaces. Now, if we were to look at what that phospholipid billayer looks like, we need to make sure that it can interact with the watery portion outside

the cell, the interstitial space, as well as the watery portion inside the cell, the intracellular space. So, the way we fix That is we use a molecule called a phospholipid. phospholipid what phosphate on the top like this as well as on the bottom because it's going to be a billayer and these phosphate groups so phosphate groups here are just these circles phosphate groups can interact with water they can basically uh stay present or facing that water without getting any issues but then we also have the lipid aspect which Is the longest largest aspect that's attached

to the phosphates so We call these phosphates an amphipathic molecule because it has a polar end, the phosphate, and a non-polar middle, which will be the lipid. And the lipid is the majority of it. But the way it works is that since we've got the phosphate facing the fluid, they don't have any issues. And the lipid is kind of held uh tucked inside forming that barrier of extracellular space or the interstitial Space in the intracellular space. Let me just jot those down once again. Outside the cell is any extracellular and then obviously inside will be

intracellular. All right. So that's how the membrane works. Okay. So it forms this sort of barrier between these spaces. So phospholipid billayer very very important. So now that the cell has a membrane, it has its own basically space inside that it can conduct all of its activities. What does the cell need To do inside of itself in order to stay alive? Well, I'm just going to sum it up as the cell's main two goals are the following. You know, the first one, it's called cellular respiration. We talked about that in a previous video. That's basically

how the cell produces ATP from our base macroolelecules, the lipids, the proteins, and the carbohydrates, specifically the monomers of them like glucose and amino acids and the triglycerides. Yeah. So, if we can Produce cellular respiration, we can produce ATP, the cell can do all of its activities. One other such activity vitally important is going to be called protein synthesis. What the heck is protein synthesis? Well, I drew in that previous whiteboard diagram that the cell is going to have a variety of proteins throughout itself like cytokeleton proteins like actin, okay, or tubulin. We're also going

to need some proteins That will be embedded in the membrane. I'll talk about why here in a little bit. We'll need these different proteins. So those proteins in the membrane, proteins inside the cell, we'll also have like the nucleus that will have some uh information in DNA inside that we need. There's also proteins embedded in that membrane. You also saw in the previous video in the in the mitochondria, you remember with the mitochondria, if this is your Mitochondria, the electron transport chain proteins were embedded in that membrane. So my question is, how did we produce

all of these proteins throughout the cell? All I want you to know right now is that the cell produced them it itself. The cell produced these proteins itself and then placed it placed the protein wherever it needed it. So for some proteins we put it in the outer membrane. For some proteins we kept in the cytool in the cytoplasm and then Other proteins we put in the nucleus membrane in the mitochondrial membrane. These proteins were produced by the cell. How did it do that? How did it do that? And then why are these proteins so

important? Well, protein synthesis, I'm not going to go through super detailed information because I just don't think it's pertinent, but I'll get you the main points here. So, with protein synthesis, what we have here is inside the nucleus, we have a bunch of DNA, Okay? Deoxy ribboucleic acid. That DNA, fun fact, per cell is about six feet long. That's a lot of DNA packed into one cell. and 1.5% of it is called genes. Those genes are segments of DNA that will code for proteins. So once again, a gene is basically one segment of DNA that

codes for a specific protein. Now you may be asking the question, whoa, 1.5% that's a very small percentage of that six feet, right? That's coding for Proteins. Uh that's kind of a fascinating phenomenon. In fact, a lot of the DNA isn't going to be genes. It's actually going to be regulatory sequences. So, a lot of the other percentages, I'm just going to put a high percentage will be regulatory in nature. What does that mean? Well, if I were a company and I have to produce a product protein. Yes, I have information about how to make

that protein, right? Uh so, let's say we're in the soap Industry and I'm able to make a bar of soap from this little bit of information, right? But how many bars of soap and what type and uh how often and how much, how little, what's the market look like? We have a lot of other bits of information that we need to know, right? In order to regulate the amount of protein being produced and also the the slight changes in type of protein. Maybe we need a certain type of soap at one point, maybe A little

different in another. That's basically what these regulatory sequences are doing. regulating how often these genes are read, therefore how often proteins are produced. Now, how does DNA have that information in the first place? How do how does a literal molecule tell us how to produce a literal physical protein? Well, we know DNA is comprised of nucleotides. Talked about that in video two, I believe. And it has letters A's, T's, G's, and C's. Now those A's, T's, G's and C's are going to in a way store biochemical information on how to build the proteins. So what

happens is a process called transcription. So inside the nucleus, transcription will occur where we go from DNA, right, the nucleic acid of DNA, and we're going to produce a transcript called mRNA. Now, I said the word transcript. That is an important word because I want you to think about this. If we have six feet of DNA packed into a small little nucleus, yes, with all this information about how to build proteins, do we want to just take all of this out to read it? Or do we just want a little bit to get out of

the nucleus to be read? Well, it'd be a lot easier if we had a transcript. Basically, a small little section. Let's say we're talking about this section. What if we had a small little section of mRNA here that coded for the protein that we wanted? Can't we just take that mRNA transcript out and it would be a lot easier rather than having to take the entire DNA out to be read? Absolutely. And so that's what we do. So in the nucleus, the cell is basically, okay, what gene do we need to read? let's write a

small little recipe on it, mRNA, and we're going to ship that out of the nucleus to then be read. And that's the process called transcription. If you need to know what happens during transcription, let's say We've got a sequence of DNA that's a A T C G. Okay, that's the letter of DNA. What will begin happening? So that's the DNA and it's actually double stranded. So we'd have an equal and opposite uh complimentary strand. But what we're going to do is only going to read one side of the DNA and we're going to produce an

mRNA transcript. Now what I want you to remember is A to T, G to C. A to T, G to C. So therefore, A's will always goes with T's. T's will always go With A's. C's will always goes with G's and C's will always go with G's. So when we produce a transcript from the DNA, we have to be complimementaryary in nature. It can't be A to A, A to A. It's actually going to be A2 and I'm going to throw you off already. U in mRNA, instead of a T, we have a U. So

A would go with T, but mRNA has a U for uricil. So therefore, it'll be U, U, A, G, G, C. You may have taken a long time in biology class doing this transcription Or translation. Uh, don't worry about it. That was just a way of your teachers to have a little more time that you can just do busy work. Anyway, moving on. Uh, so this MRNA transcript is now UU A GGC. That being said, you see that there's letters here. Yes, there's letters here where the letters are going to code for, can you guess?

The letters are going to go code for a specific amino acid. A specific amino Acid. Why? An amino acid is the base unit of a protein. So as an example, what would happen in the cytoplasm is the ribosome would sorry the mRNA would make its way to what's called a ribosome which is actually produced from our RNA from the nucleololis. Don't worry about it. So this is going to be a ribosome. And what the ribosome's job to do is to place the right amino acid with the corresponding mRNA sequence. So, think of the ribosome as

the little chef that Is going to use that recipe of mRNA to produce the right protein, which can just be the product that we're producing, right? So, how does it work? Well, the recipe goes in, we actually read it in sequences of threes called codons. So, there will be codons that we use, three sequences of letters. In this case, it would be u UUA. And that would code for a particular amino acid. From there, we've got an amino acid chained. This GGC would go through and then we'd Make another amino acid on top of it.

It would go eventually until it's told to stop and we would produce our protein. Now, as a reminder, this process from mRNA to protein or polyeptide, you may hear either one, is called translation. Basically, we're translating the information on the mRNA to the protein itself. That's why it's called translation. Don't miss the forest for the trees. The goal of this whole process right from DNA to mRNA from mRNA to protein is to make the protein itself because the proteins are the structure and function of the cells. So as an example that protein maybe it's a

protein of tubulin that produce this little cytokeleton to hold the cell up. Maybe it's a protein that will be embedded into the mitochondria and serve as the electron transport chain. Maybe it's a protein that's embedded into the main membrane to help things in and out when we want Them to. All in all, this whole process is just to get to the point where we have a physical protein that can do something for the cells. Okay. Two connections here that I want you to make. Number one, do you think every cell reads the same genes? Do

you think every cell reads the same genes? Well, if you remember what I just taught you, do all cells look the same? Are all cells structured and functioning the Same way? Absolutely not. So, I want you to remember that cells only read cells only read the DNA or the genes that are important to its own function that are important to its own function. That is a weird concept. That is a very weird concept. Uh because think about it this way. If you have a big recipe book, DNA, if you have a big recipe book at

home, okay. Um, at 6:00 p.m., are you going to open up to the Breakfast page or the appetizer page or the drink page? Okay, maybe you will if you're like a I don't know, if you like uh breakfast for dinner and you like certain drinks. Anyway, you get the picture. you're gonna actually open up to a specific dinner page, a dinner recipe that is pertinent to what your family wants for that evening. Okay? So, once again, with your recipe book, you only read the part of the recipe book that's pertinent to that moment in time

For your family. In the same way, if you are a liver cell, you're going to read the genes that pertain to a liver cell's function. If you're going to be a muscle cell, we'll learn about the muscles later on. You're going to read genes for measin, you know, the meosin gene and the actin gene for your skeletal muscles because skeletal muscle is just packed full of those two proteins to help with their function. So therefore, each cell reads The genes pertinent to its function. How do they know how to do that? That's above my pay

grade. not actually above my pay grade, but it has to do with the biochemistry within the nucleus itself. Super fascinating. If you want to learn about it, you can look up methyl transferases um and gene expression. But we're going to move on. This is an overview of A&P1. So, let's continue moving forward. So, therefore, we just produce proteins, right? We've already Learned about cellular respiration. If the cell is capable of doing both of these things, the cell will remain happy and functioning. But you'll notice that a lot of the proteins are inside membranes. You see

that, right? That's because one of the main topics we need to understand with cells is cell transport. What do we get out? What do we bring in and when and how much. And all of that is going to be regulated by the cell membrane and the proteins Inside of it. And can you imagine if there was a protein here that let in a very important nutrient, say glucose, right? Let's say glucose is this uh this protein is like a glucose transport protein. It allows glucose to come inside of the cell. That seems like a pretty

important protein, right? Well, where did that protein come from? Well, it came from a ribosome that made it by reading the recipe, the mRNA recipe for that glucose transport protein that was Inside the nucleus, inside the DNA. So, there was a sequence of DNA called a gene for that glucose transport protein that was read, transcribed, translated, and then made into that particular protein. You would say that that's very important for the cell's function so that it can produce energy from that glucose. Yes. But what if in that gene rather than being say an A, what

if the DNA was screwed up and it was instead a C? There's a mutation in your DNA. Maybe you got that mutation from your parents. You were it was transmitted on to you genetically that your parents already had that mutation. They gave it to you or it just happened willy-nilly in the middle of your life. Well, now the mRNA isn't going to be a U anymore. It's instead, I'll draw in a different color, going to be a what? A G. Do you think that gua codes for the same thing as UUA? Potentially not. Potentially not.

And if we now have the wrong transcript, what do you think? We're going to also have the wrong protein. So what if now we have a missshapen protein for the glucose transport protein? Now it's misshapen. What if now after using or after having that mutation, that change of the DNA, what if now that protein looks instead like this? Do you think that glucose can get in Now? No. So now glucose can't get in. Do you think the cell's going to survive very well? Probably not. Probably not. So what that is once again is called a

mutation. So a mutation is basically any change in your DNA. Okay? Any change in your DNA. It can be really bad. It can be fine. It can be good. It can not affect you at all. Uh but it's just a change in DNA. This can be given to you by your Parents genetically. So they've already got a mutation. They pass it on through the sperm or egg. And now all of your cells have that same mutation. or you could accumulate the mutation throughout your life. Now, that change in DNA, that mutation, like I said, could

turn out to be bad. The protein could be misshapen and bad and not function properly. It could actually turn out to be just fine. It could be normal. Maybe that change in the letter codes for the correct amino Acid and we're fine. That's possible, too. But the more mutations we have, the higher the risk factor for different genetic disorders. So you'll notice that genetic disorder is usually just based on the wrong shape of protein. Very simple example before we get into membrane transport is cickle cell anemia. Cickle cell anemia is basically when your red blood

cells instead of looking like this they look sickle-shaped. Well that is because There is one letter that was changed in your DNA that changed the shape of the hemoglobin protein and now the protein can't structure properly. it can't function properly and it sickles. So, mutations are a really fascinating concept. We don't have a ton of time to get into it in this video. Um, but just know that any change in DNA could potentially change the protein structure, therefore change the function. And anything that happens in That case that's bad is called a genetic disorder. So,

I'm hoping that you're recognizing that basically all disease happens on this molecular level, right? All disease happens on a molecular level. Why? because a protein a macroolelecule is wrongly shaped and so now a function is vitally off. Yeah. So it's important to understand how these things work. So to further clarify that point, we need to talk about some proteins, some voltage of the cell Membrane. Then we're going to talk specifically about water movement and tonicity and osmosis and what could go wrong there. And then we'll be out for the day and we'll be moving on

to the next lecture. So keep watching. You guys are doing great. All right. All right. So, for this section, I want to draw together because we're going to talk about specific proteins in the membrane, as well as just some things you need to know about those two sides of the Membrane that are really important, especially when we get to the nervous system and the muscular system. So, first, let's just draw a membrane. I would prefer in pencil uh because we're going to erase parts of it and draw some proteins inside of it. So, let's just

draw a big rectangular square here to represent our cell. Okay? and we're going to talk about the membrane and some of the proteins and how they go in and how they allow things In and out, that type of thing. So, here's your cell. There's the cell membrane. Now, one thing I want you to know about the cell is inside of the cell and outside of the cell, it is a fluid-like environment, right? We talked about intracellular, extracellular, and we know that there are electrolytes within it, right? We know that the blood has electrolytes like sodium,

calcium, etc. And it's going to be bathing the cell. But the electrolytes are not in The same amounts inside or outside of the cell. Let me give you an example. Sodium loves to hang out outside of the cell. Sodium loves to hang out outside of the cell. And actually in the bloodstream, you have a pretty good amount of sodium in your bloodstream. Therefore, inside your cell, you have a relatively low concentration of sodium. We'll talk about why here in a little bit. Secondly, we know that potassium is Actually very high inside of the cell. Think

of cells as potassium bags. Whereas outside of the cell, potassium is actually relatively low. So in your bloodstream, it's actually a pretty low amount of potassium. And then from there, we also have very low amounts of calcium inside of the cell, but a decent amount of calcium outside of the cell comparatively. Now, that doesn't mean that we have the same amount of sodium And calcium outside of the cell. This is all just relative amounts. Relatively speaking, there's more calcium outside the cell than inside. Relatively speaking, there's more potassium inside the cell than outside, etc. So,

let me ask you this. Where does sodium want to go right now? You all should say one of the core concepts, high to low, sodium wants to go into the cell. Where does potassium want to go? Out of the cell, high to low. Where does calcium want to Go? High to low. Into the cell. You see the picture? Why can't they? They want to, don't they? There's this there's this potential energy where sodium wants to flow from high to low because things in nature like to flow high to low. It's called diffusion. Why can't they

diffuse? Why can't they go high to low right now? Well, because we talked about this earlier on. These things all have a charge. They are all polar molecules because they have a separation of charge Within themselves and the membrane is non-polar. So therefore, polar things cannot cross the nonpolar membrane. So if we want to let these things in like sodium and calcium in or maybe potassium out, we have to use a polar protein in the membrane. So we're going to talk about several membrane proteins that can uh facilitate the movement of these electrolytes here in

a second. But what's fascinating is that inside of the cell, you actually have a pretty strong Negative charge. So what I want you guys to do is just draw inside the cell maybe in a red negative charge. So inside the cell's negative charge specifically it's along the membrane. So the inside of the membrane is slight negative charge. And interestingly enough outside the cell is typically more of a positive charge comparatively. Once again this is just a comparison from outside to inside. Now, you may think, "Oh, that makes sense because there's more positive ions Outside and

less um potassium outside and vice versa." But aren't these all kind of positive? Wouldn't that make it wouldn't really really make a difference because they're all positive? Well, I want you also to remember this. As I drew in red, there's a lot of really big molecules inside the cell like this. And these are all our proteins. Inside the cell, there's a lot of proteins. And proteins are typically a pretty strong negative Charge. So what's really interesting is that inside the cell because we have a lot of negatively charged proteins inside the cell, the inside of

the cell remains at a negative voltage. In fact, if you took a voltmeter and you poked it into the cell, it would measure give or take from negative, it depends on the cell, from negative maybe 90 to about60 molts. We'll typically talk in this class at a resting membrane potential of negative70 millolts. And like I said, This is our resting membrane potential. What does that mean? Well, for your sake right now, just know that when a cell is negatively charged, when a cell is negative, the cell is hypothetically doing nothing. Okay? It's not necessarily active.

It's not it's not going to do something cool. Okay? As an example, right now I can show you that my shoulder muscles, these guys right here, are at their resting membrane Potential. They're negatively charged. Now, inside of these muscle cells, they are positively charged. So, when cells become positively charged, so when positive charges flow into the cell, what will happen? Something cool. They'll contract. They'll send a signal. They'll do something interesting. But when they are negative, they're typically not doing that cool thing. Okay? They're not excitable right now. They're calm. They're just chilling, but They're

still doing their other functions. They're making ATP. They're making proteins, etc., but they're not doing something cool like contracting the muscle or sending a signal. Okay? Kind of a weird concept. You can't really grasp it yet until we get later on. But just put it in your memory banks. Inside the cell, negative, outside of the cell, positive. Just put that in there. Now, that being said, let's come back to these ions and how we Can let them in or out. So what we're going to do is we're going to draw a variety of proteins on

the outside and we're going to talk about what could be happening in these different protein cases. So I'm going to draw all these proteins. I'm going to do in a new one. I know drew in red. Let's do orange. Uh just to give a little different. So in the membrane what I'm going to draw is some general proteins that you'll find throughout the rest of this class. Right Here let's draw one that kind of looks like this. Kind of looks like this. You see how it's always open? So it's always open and things can flow

in or out wherever the heck they want. We call this some form of a leak channel. Great name because it's literally going to allow things to leak in or out of it. Now anytime in A&P we will clarify well what is leaking? What specifically is leaking? Because these proteins are going to be very very very specific to One thing typically. So if I were to say this is a potassium leak channel, potassium leak channel, it's always open, always open for business. You can now tell me what will be occurring constantly. Well, if it's for potassium,

it's going to allow potassium to move through the membrane through this protein. Where's potassium going to want to go? Well, as we mentioned, potassium always wants to flow high to low down its own Concentration gradient. So potassium through these channels will constantly be leaking outward. Does that make sense? Okay. So if we lost a positive, what's interesting is I can draw a little graph here. If this is the only protein in the cell and the cell is at that 70 right here, what would the charge of the cell begin to do? It would probably go

down, right? Because we're losing a positive. If we lose a positive, we become more negative. If You become a less positive person, you're a more negative person. Yeah. So that is potassium diffusing flowing high to low out of the cell. Now let's look at some other proteins that we could look at. So by the way this leak channel I said is potassium leak channel I always get the question in my class is that the only one? No. There's typically other leak channels of other sorts. There could be like a hydrogen ion leak channel. There could

be a chloride leak Channel. But we'll always clarify what the heck they are. This is just teaching you the generalized proteins so you can apply them later on. What about another one? Well, let's say we've got another protein that looks something like this. Something like this. You notice how it's closed, but then we have a little whoop little sort of receptor looking thing, right? What this guy is is a liand gated channel. Liand gated channel. Liand gated channel. Well, what the heck does that mean? Well, think of this as just a lock and key mechanism.

The liand will be the key and the key in this case will be some sort of circular molecule that can fit into these receptor sites. So this will be the key. When that key sometimes it's a chemical, sometimes it's some sort of other thing. When it binds to the receptor site, that channel will then pop right open. So whenever the key is in the lock here, That gate will be open. So if I were to say hey this is a liand gated sodium channel you would say hey when the lian isn't present when the key

is not present sodium can't get in but as soon as that lian that chemical becomes present sodium is now allowed to flow high to low into the cell. This is a great channel to in a way mitigate or uh control when we let sodium in. You will see that in the nervous system at the neuromuscular junction when a neuron Sends a a chemical signal. Okay, so a chemical it will open up these lig gated sodium channels in your muscles and when the sodium flows in we make the cell what charge? Well, we'll probably make the

cell positively charged here like maybe like positive 10 molts and that is when contraction happens interestingly enough. So do not do not you're I bet you money you're starting to check out in this video like why is this important? It's be important because This is going to be applied in later chapters and also there's several several disease states like tetanus like myinia gravis that are directly related to one protein channel. So don't say that it's not important. We'll see that it is important later on. Moving on. So that's one type of channel lig gated channel

lock and key. We also will have others that are really fascinating and we call these guys voltage gated channels. So I do a little Harry Potter Thunderbolt there. So once again these are called voltage gated channels where basically we will have a change in voltage and a certain threshold voltage a specific voltage number these guys pop open. So I'm just going to say open and close at a specific voltage. So open and close at a specific voltage. Okay, so let's say for example, maybe some of These channels started opening up, right? So now sodium's starting

to flow in. Well, now the the the cells getting a little more positive. Maybe we reach a specific amount that will pop these guys open and maybe these are voltage gated calcium channels as an example. So now calcium starts to flow in and something else happens. Okay, so once again, they just open and close certain voltage. When the cell changes its voltage to a specific degree, we open or close those Guys. We'll see those later on in the neurons and muscles. Then lastly, for this part, we're going to talk about mechanically gated channels. These are

pretty cool. So these will be mechanically mechanically gated channels. And these have levers on them of some sort or like spring-loaded. And anytime there is a specific amount of force on them, they will pop right open. So now The levers will show are like down. And so since there's a force being applied, then they open up and maybe these are mechanically gated sodium channels. And so now sodium will begin flowing inward. Okay, you get the picture. You're noticing that there are different stimuli that open different channels, right? Chemical voltage or mechanical force, right? Great example

of this is if you were to touch one of the hairs on your arms, right? You're Putting a force on the hair and there's a protein inside the neuron there that is detecting that force and the protein changes its shape, allows sodium in, sends a signal back to your spinal cord and your brain to tell you what is touching you. So again, these guys are all going to open and close with different stimuli. Very, very important. Now, you're noticing all of these guys, all of these guys are flowing high to low. Yes, they're flowing high

to low Through a specific protein. What all of these are called, everything we just drew on the top, this is all processes called facilitated diffusion. facilitated diffusion. That basically means diffusion high to low. Facilitated all it means is it's using a protein. It's using a protein to allow that flow of a specific thing through itself. So all of these were facilitated fusion. Hyalo through a protein. Very cool. Now Simple diffusion you may be like oh well this is facilitated. What's just diffusion by itself? Well that is when say we have oxygen. Okay, say we have

oxygen outside the cell in pretty high amounts. Oxygen is just going to flow high to low into the cell. That is just called diffusion. It's not facilitated. Why? It's not using a protein. It's just going right through the membrane. So remember, non-polar objects can just Pass right through the membrane. High to low, things like gases, things like fats, and they'll just flow high to low down their concentration gradient. Wonderful. Now, on the bottom here, we're going to do a little more interesting transport that's going to be called either secondary or primary active transport. So, on

the bottom here, we're going to draw different things that are going to facilitate active transport. Now, with diffusion, things flow to high to low without any energy present. Right? If we just like drop this marker, it's going to flow high to low. If we just open these channels, things are flowing high to low. But with active transport, notice what I did once the marker dropped. It flew high to low, but now I'm using some energy to bring it low to high. Yes, that was hard. That's why I had to sigh. So, with active transport, we're

typically going To move things from low to high using specifically ATP energy because ATP is that usable currency for our cells. So just like I mentioned in the previous video, ATP when we clip off that phosphate, when we go from ATP to an ADP and a phosphate, we have some sort of energy that is being released from that. Yes. So when we release that energy, we can do something cool. And in this case, it's going to be moving things from low to high. Let me give you the first and Most important example of this. We

have a protein inside most of our membranes for all of our cells, all of our cells called the sodium potassium ATPAS pump. Sodium potassium ATPAS pump. You know a couple of things about this already. Number one, there is an ATPAS. Remember that is just an enzyme that's going to break apart who? ATP. So, we know if we bring a molecule of ATP here, there will be an enzyme, a little Scissor here that will clip it, turn it into ADP and a phosphate, and it'll do some sort of useful work for the cell. Well, what sort

of useful work are we going to be using? Well, we're going to be moving or pumping sodium and potassium. Now, in this case, this is where you might get a little confused, but I got you. The pump is going to pump things from what? Low to high. Where will potassium go? We're using energy. Potassium is going to go in. Where's sodium going to go? Sodium, it's going to go out. Why? Because it's a pump. It's a pump. It's pumping things from low to high concentration. We're pumping potassium from low concentration outside the cell to high

inside. We're pumping potass or sorry sodium from low concentration inside the cell to high concentration outside the cell. How did we do that? We needed to use energy ATP. So when we clip that phosphate off, we do useful Work. How? Pump potassium up its concentration gradient. Pump sodium up its concentration gradient and therefore we have now high sodium outside the cell and low high potassium inside the cell. That's how we got these two things high and high by using this pump. Fun fact, about 60% of your calories go towards firing this one protein in virtually

all of your cells, especially in your brain, spinal cord, and muscles. So, this is a Vitally, vitally important pump inside your cells. Why? Why are we doing this? What's the point? Well, number one, now that we've created this concentration gradient by using ATP, we can now control when things come in, right? Because now if we open this protein, boom, sodium flows in. And boom, if sodium flows in, maybe calcium flows in because this voltage gain channel opens. And now the cell is positive. And now the cell contracts or Sends a signal or does something for

your body. So why do we use so much energy towards this? It's because we're creating a condition, right? High sodium, high potassium to now allow things to flow in and out when we want them to so that we can control our movement. So we control our thoughts, etc. Okay, so that is why that pump is important. We also see it in a variety of other places. Let me show you another protein that benefits from him. There Will be a couple here. Let's draw one here. And we're going to draw pretty big. It's going to have

kind of two tracks here. So draw just slightly like a dotted line in the middle. We can call this just a simp protein. Simport protein that just basically means same direction of transport. There are certain ones called sodium glucose imports. Very common one. Sodium glucose imports where we have sodium being high outside The cell that really wants to flow where? Always high to low. So it's going to flow high to low into the cell. But in the process, it's actually going to pull a big molecule of glucose in with it. Now, think about this. Glucose

is C6H12 06. Really big molecule. Big molecules. Uh, I'm going to make a joke. This is bad, but physiologically it's accurate. It's a big molecule that doesn't like to move. Just like really big people a lot Of the time don't like to move. I hope that doesn't offend anybody, but it's just harder to move a larger object of mass, right? So, this big molecule of glucose doesn't really want to go anywhere. Even if it is high out here and low in here, it's just hard to get it in because it's so big. But if we

use a simp, then the power of sodium compels glucose to come in. I like to tell a story in my class about how I got kidnapped by my best friend Rob, who Wanted to go to a horror movie because he's really interested in horror movies, but I have no interest in horror movies. But he was so strong and so motivated that he literally kidnapped me from my house, drugg me to the movie theater, and made me watch it with him. Well, I was glucose. I was content where I was. He was sodium. He was very,

very eager to get to the movie, get to the cell, right? So, he drugged me in with his energy. How did that energy come about? How did this energy come about? How did sodium get so high out here in the first place? Sodium potassium pump, right? And that was only made possible by that pump. So in a lot of cases, especially like an intestinal absorption where we're absorbing glucose into the body, it uses these sorts that are essentially powered by the gradient created by this sodium potassium ATPAS pump. All right, so a lot there. Hopefully

that made sense. We Call this process after this one secondary active transport, secondary active transport. Whereas this one over here would be primary active transport. Why? Because primary active transport as you can guess directly uses ATP. But then secondary active transport usually uses the gradient produced by the primary active transport action. All right. So another example of a of a protein that benefits from that is something called an antiport. We won't See this really until the kidneys later on. So an antiport is basically the same thing, but in this case anti means opposing directions. So

in this case, let's say we got a I don't know sodium hydrogen ion antiport. Sodium super high out here wants to flow in, but it's going to be like a revolving door because then hydrogen that doesn't really want to move, hydrogen ions wants to get kicked out. Okay, typically from low to high Concentration. All right, so that'd be an example of antiport. Once again, sodium flowing high to low and then charging that hydrogen to get out. But again, there's other types. Just remember, hey, we're using the gradient produced to make some sort of thing move

that doesn't necessarily want to. Okay, so those are some antiports, but we also have other ways to transport large things out of the cell. One example is going to be called exocytosis. and one Will be called endoccytosis. So exo or endoccytosis basically means either outside the cell or into the cell. This is where the cell will package up a product inside of a vesicle. It's basically a membrane inside the cell. So here's a vesicle. Okay, we'll see this a lot later on. So we basically have a membrane outside of it and then we have some

form of product inside. Whether it's a chemical, whether it's fat, I don't know, we've got some Sort of product. Well, exocytosis is when we would spew that out of the cell. The membrane fuses with the outer membrane and delivers all of this stuff out of the cell. That's exocytosis and it requires a lot of ATP. Same thing with endoccytosis. Endoccytosis would be say, hey, there's a product outside the cell that we want to bring in. So it will encapsulate it with its membrane and bring it into the cell and that is a process called endoccytosis

and once Again that takes a variety of ATP molecules to do as well but it's just for things that are too big to get in or out. So as an example your white blood cells do something called fagocytosis where they engulf a bacteria. So that's a form of endoccytosis and it requires a lot of energy inside of them. So this is all active transport. You notice we have ATP, active transport, using energy to fire a variety of different things. But there are also some other membrane Proteins I want to discuss that will be very big

implications in A&P2, but also in A&P1 if you have the endocrine system in it. So let's say we have another membrane here and we're just going to draw a couple more proteins. So we're nearly there and then we're going to talk about osmosis and then we'll be done for the day. Now, one main protein that will be very very important will be this guy that's kind of got this cool looking receptor shape on one side and Then it's got seven transmembrane loops basically meaning between the membrane and outside of it and then a little block

here. What this is called is a G protein being the rectangle coupled with a receptor. Groin coupled receptor. The receptor would be that part. So we got the G- protein being this guy right there and the receptor being this guy right there. Does that make sense? So we've got a receptor and a G- protein. What happens here is some form of a signal maybe it looks like this. So here's some sort of signal looks like a music note. Usually the signal is a hormone fun fact or a drug. That signal binds to the receptor and

immediately what happens is that G- protein or a subunit of the G- protein will activate. Okay? Okay, so that G- protein then activates. That G- protein activating will then go doing some sort of useful action for the cell. So I'll just say Useful action for the cell. Okay, that'll come up a lot. The second one I want to point out will be these proteins that look something like this. They've got a main protein branch, but then interestingly they will have a carbohydrate chain on the outside. Maybe that looks like this. This is called a glyco

protein. Why do you think it's called a glyoprotein? Because glyco means carbohydrate, the Blue part. Protein being the block part that's embedded in the membrane. And a lot of the times these can be used as ID markers, ID tags. So you'll have cell uh ID tags on the outside of your cells that basically say, "Hey, I am a human cell. Do not kill me, please." Because white blood cells are patrolling. And if they see a foreign ID tag, that white blood cell will attack you. So as an example, if you look at a bacteria, the

bacteria Also have these glyoproteins on the outside and your body will notice those as foreign and attack them. But it will notice your ID tags and say those are normal. Don't attack them. So we'll use that a lot uh in the immune response, these ID tags, the cellular ID tags. And then lastly, but not leastly, that's not a word. Uh we'll also have other proteins that kind of look like these welding marks like this. And these are just a specific type of integral protein That typically binds cells together. So binds cells together typically called integral

proteins. These can be called desmosomes. There can also be hemisesomes that anchor cells to the extracellular matrix. Those are very common in connective tissues. So just know there's proteins in the membrane that will help anchor cells together. As you can see, like our skin cells are all anchored together. They Don't pull apart easily because there's a lot of proteins interlocking between the cells, keeping them secure and together. I hope you notice the amount of times I've said protein, right? Proteins regulate transport of the membrane. Proteins regulate how well cells connect together. Proteins regulate signaling. Proteins

regulate moving things out or inside the cell. Proteins really are the structure and function of your cells. And all of it came together by the cell reading its DNA, transcribing it, producing the protein at the ribosome. And now we have all these incredible functions of the cells. So the last thing we need to talk about is the implications specifically of water movement, osmosis in and out of the cell and how it can relate to clinical application. So we'll get to that next. Can I just say you guys are doing fantastic. If you need any other

helpful Resources, please, if you're on YouTube, you can check the pinned comment below or the description. But for the meantime, let's finish up with osmosis. Let's define it first. It's a great little definition. So osmosis, it's not Jones if you've seen that movie. Osmosis is simply the diffusion of water. Diffusion of water. You can add across a semi-permeable membrane, but it's just diffusion of water. It's water, right? The molecule H2O Flowing from high concentration to low concentration. So, does this hold true with the high to low concept? Certainly does. But I also want you to

write the following definition that may not make sense to you quite yet. The osmosis, not only is the diffusion water, it's the water movement from water moving toward the high solute Area. Water moving towards the high solute area or water moving from low to high solute. H sounds weird. Sounds weird, huh? Well, let me just show this to you. Let's say we have okay a little uh beaker. Here's your little beaker. And we're going to have a little membrane here. Imagine this is the membrane of the cell. Okay? And let's say one part of the

membrane we're going to draw in one way and the Other we're going to draw in another way. So over here, let's just draw a ton of blue dots. These are going to represent our water molecules. Okay? So this is all just water molecule. It'll just be the dot. So we've got water molecule over here, water molecules over here in pretty relative concentrations. All righty. Now differences is on one side we're going to draw a crap ton of solute. So a lot of solute. You may be saying What the heck is a solute? Solute is basically

anything dissolved in the water. Anything dissolved in the water in this case. So we've heard of several solutes before like sodium, like chlorine, like calcium, like potassium. These could all be solutes. Glucose could be a solute. Anything dissolved in in water is a solute. Let's say this is where all the solute is and this is where none of the solute is. Well, let's think about this. If I were to take just a box of this, just like this much box. Okay, this much box. How many solutees per water molecule in that one? Well, there are

two solutes, two triangles per three water. Yeah. Whereas here we have zero solutes, right? Zero solutes per three water. Well, what's the difference? We can say that this one is more concentrated, right? More concentrated. we have more solute per water. Whereas in this one, We have a less concentrated solution. There's less solute per water. So, we can give some numbers to this to help us realize this. First off, we need a new unit called M OSM. This is just standing for mill osm moles. And it's just going to measure how much solute per water or

solvent, which is always going to be water. So, how much solute per water? Well, let's say this one right Here is something like 290 millos moles because it's got some solute concentration, but not a ton. Whereas this one would actually be zero millos moles. And what if I had a different beaker that looked like this where instead it's just like ah a ton of solute ton of solute in like one water. Well, this one might be like a thousand millosmals. You see the difference? So the higher the millosmal number, the higher the Concentration, the more

solute there is packed into that solution. So why is that important? Well, let me break it down for you. If we have a lot of solute over here, less solute over here, water wants to flow where? That way. Water wants to flow that way, right? So why is that? Well, water is moving towards the higher solute, is it not? Water is moving towards the high solute area, but it's also following its own concentration gradient. There is More water per solute here, less water per solute here. So water flows from high to low water. Better drawn,

it would almost look more like this. There's just less water on this side in general because it's just packed full of solute. Yeah. So less water over here, more water over here, high to low water. Or we can also say water wants to move from low solute area to high solute area. Just to give you some number examples, zero millos fluid is pure Water. That's pure water. So if you have pure water, it is zero millosmals. Why? There's no solute. 290 millosmals is actually our blood solute concentration. It's actually a homeostatic set point. A th00and

is actually ocean water. Okay, that's a really highly concentrated fluid, right? Because you got salt in there, you got other gunk in there. So it's very high in million moles. So two things. Number one, how Does this relate to IV solutions you give to your patients? So, I'm gonna write these down. So, for IV solutions, how does this relate? As well as if I'm stranded on a boat in the middle of the ocean, should I drink the ocean water? Should I drink the ocean water? And what how does this relate to IV solutions? Let's get

into that. Well, let's start first with talking about our cells because it all comes back to cells. So, if we have a cell here, okay? And we've got the bloodstream always bathing it right outside of itself, we need to know, hey, what's going on here? So, first off, we've got 290 millosmo blood, right? Well, guess what concentration your cell is? Well, your cells are also 298 millosmol. So where does water want to go? Remember water always follows solute. So essentially we can say hey if it's a lower milliosma one place we're going to Move from

the low number to the high number. Right? Where does water want to go here? It doesn't. There's actually going to be equal water movement in and out. We call this an isotonic solution. Iso meaning same tonic meaning tonicity or solute concentration. So this is our happy model. This our happy model where it's same concentration on both sides. But what if I were to drink ocean water? What if I were to drink Ocean water? I take this thousand millosmal ocean water and I'm going to throw it where? Well, I'm going to drink it. Where does anything

I drink go? Into my bloodstream. So, I'm putting highly, highly concentrated ocean water into my blood. What will my blood likely do? It will probably rise. So, let's say it goes up to 400 mills. That would kill you, but let's just say that number just for easy. What we have now is no longer isotonic. We're Not the same osmalerity. We actually have something called a hyperttonic solution. What that means is that this solution right here outside the cell is high hypertonic high concentration compared to the cell. So hypertonic means high solute concentration outside the cell.

Outside the cell. So where will water want to go? Water always wants to go as we remember towards the higher milliosmal number. So What will happen is water will leave the cell and if water leaves the cell the cell will now creatate or shrivel shrivel it'll shrivel up and if the cell shrivels up we likely lose structure we likely lose function. So we don't want to have a hypertonic solution. So therefore, we should not drink ocean water because all of our cells will shrivel and we will die bad. Yes. IV solution. Well, fun fact. Did

you know that you could kill somebody simply By giving them pure water in their IV solution? Let's try it out. Let's say somebody's super dehydrated, right? We need to give them pure pure water because they're dehydrated. They have low water, right? So, let's instead I'm going to redraw this. Let's say we have the bloodstream and we're going to give them pure water. Sounds so good. So, we hook up an IV. We put Aquafina on the IV bag and let's see what happens. Well, now we're giving them pure water. Let's Say now your blood is zero

milliosmos because it's pure water, right? That's never going to happen, but we'll say it is. Where will water want to go now? It'll want to fly into the cells. Fly into the cells. This is called a hypotonic solution which basically means the opposite low solute concentration outside the cell. So now water will fill the cell and the cell will lice. It will burst. It will Break apart because it doesn't have enough space to hold that water and it will die. Lice means to blow up and die in this case. So you can't give a person

pure water in the IV. What number osmalerity do you want your IV solutions to be? But you probably guess you want your IV solutions to be 290 millosmals, right? Because then there will be an equal movement of water in and out of the cell to keep the cells of the right shape and Therefore the right function. Now you already knew this. Why? Because if you've ever worked in healthcare, you've probably seen IV bags that say, "Hey, N% NAC. That means that that bag of fluid has.9% sodium chloride and the rest is water. That is equal

to 290 millosmol because you're trying to keep the osmolerity, the concentration of solute in your blood the same as your cells to keep them the right shape. All right? So That's why osmosis, the movement of water in or out is very important when it comes to what we put in our patients blood. Now the last little tweak, we know that water is a polar molecule, right? Water is polar. What do we know about membranes? They're non-polar. You guys should have been correcting me this entire time, right? This is a non-polar membrane. Can water pass through

it very easily? No, it cannot. And in fact, you will need Some proteins called aquaporin proteins embedded in the cell membrane, which most cells have that allow that water in and out. But do not forget the core tenants that we've taught up until this point. Right? Membranes are are non-polar. water can't pass through. Now, sometimes it can if the concentration is great enough, but most of the time you need aquaporins. It's very important when we get to your kidneys. Thanks for watching today, Everybody. Be sure to check out the next lecture in this series, and

please ask me any questions you have in the comments below. Thanks, everybody.