The Cell Membrane

in this video we're gonna talk about the cell membrane and we're going to identify the components that make up that membrane now the first thing we're gonna do is talk about something known as the fluid mosaic model so this model describes the cell membrane it tells us that the membrane is fluid which means that the phospholipids are free to move in any direction in this membrane even the proteins highlighted in purple they're also fluid they can move about in this membrane as well the word mosaic tells us that this picture is composed of many different parts the membrane is composed of phospholipids proteins and glycoproteins glycol lipids cholesterol and things like that so there's many different parts that make up the cell membrane but the first component we're going to talk about is the phospholipid in red the membrane is mostly composed of phospholipids the phospholipid has a polar head and two nonpolar tails so keep in mind the phospholipid is composed of a phosphate group it has two fatty acid chains and it also has a glycerol molecule the two fatty acid cells are nonpolar which means that they're hydrophobic they don't like water the polar head is hydrophilic it loves water water exists in the extracellular fluid outside of the cell and it also is present in the intracellular space that is inside of the cell so all of the phospholipids the polar heads are faced toward water the nonpolar tails are faced away from water in the interior of the cell membrane now here's a question for you and what word describes the dual polarity nature of a phospholipid we said that a phospholipid has a polar Hydra flic head and two non polar hydrophilic tails there's a word that describes a molecule with hydrophobic and hydrophilic parts what word is that that word is amphipathic phospholipids are amphipathic because they're both hydrophobic and hydrophilic so they make up the phospholipid bilayer of the cell membrane so that's the first component of the cell membrane that you need to be familiar with now the cell membrane is consists of a lot of proteins and there's different types of proteins they're highlighted in purple what do you call this protein right here so if you see a circular protein it's known as a globular protein and the fact that it's on the exterior it's also called a peripheral protein this protein here is known as a surface protein because it's on the surface of the phospholipid bilayer now how would you distinguish these two proteins what would you say by the way this is another peripheral protein but it's not a globular protein now how would you distinguish between an integral protein and a transmembrane protein this protein here is known as a transmembrane protein I'm just going to put TMP for that since I'm running out of space a transmembrane protein spans across the membrane so as you can see part of it is outside of the membrane and the rest of it is inside of the membrane this here is called an integral protein an integral protein is embedded within the membrane now a transmembrane protein is also an integral because for them to span the entire membrane they also have to be within the membrane as well so all transmembrane proteins are integral proteins but not all integral proteins are transmembrane proteins so as we said before this is both a transmembrane protein and an integral protein but this right here is an integral protein and not a transmembrane protein now I had to clear away a few things because the pagers getting crowded now one thing I do want to mention is you could also have a surface protein on the inside of a cell but it's on the surface of the membrane and some of these surface proteins they could be anchored to the cytoskeleton network of the cell through filaments now some of the surface proteins and also the peripheral proteins they could function as enzymes so they can speed up chemical reactions within the cell as well now here's another question for you what's the difference between these two structures there what are they called so here we have a protein attached to a sugar chain those hexagonal shapes represents the six carbon glucose unit so we have a carbohydrate attached to a protein so this is called a glycoprotein many glycoproteins which are found on the surface of cellular membranes they play a role in the immune system with antibodies they function as a self recognition and cell the cell interactions now over here notice that we have a sugar unit attached to a phospholipid so in this case this would be a glycolipid which also plays a role in cell the cell interaction and cell signaling now the next thing we're gonna talk about is how things flow into and out of the membrane the cell membrane is semipermeable which means it allows certain things to get in while blocking other things will prevent other things from entering the cell now small nonpolar molecules can easily diffuse into or out of the cell so when you take a breath when you breathe in you're breathing in Oh two oxygen flows into the cell because the cell needs it and then when you exhale you breathe out carbon dioxide so carbon dioxide tends to flow out of the cell so both of these molecules are nonpolar small molecules they can easily pass in and out of the cellular membrane now water is a small polar molecule and it turns out that water can diffuse through the membrane but it can't do it easily it's a very slow process because water is polar and it doesn't mix well with the nonpolar interior region however because the concentration of water is so high inside and outside of the cell some of it will force its way through the cellular membrane but now there are special proteins that can easily transport water into and out of a cell and these are called aquaporins so this protein right here this integral protein also serves as a protein that transports stuff a protein that transports water through the membrane as you said before aquaporins water can flow into or out of you know that protein so if you drink a glass of water what is gonna flow into your cells if it's a hot day and you're joggin and you're sweating you're dehydrated water is flowing out of your cells so what can go in either direction now what about other particles let's say like an ion potassium and sodium can they flow into an cellular membrane now ions they can't flow in and out of the cellular membrane without the help of a transport protein so they can't just pass through the membrane their charges are significant greater than water water is neutral but it has partial charges which makes it polar ions have a complete full positive or negative charge so they just can't flow through the membrane without the help of a transport protein so the protein that they need is called a channel protein specifically this known as ion channels so the ion channels will help sodium and potassium to flow either into or out of the cell one example is the sodium potassium pump which I'm not going to go into detail into this video so integral proteins they could serve as channel proteins they could serve as carrier proteins and things like that now this right here is an example of a carrier protein let's say if you have a big molecule like glucose the carrier protein can take in glucose and then this part can close this part will open and then glucose will travel through glucose is a big polar molecule it can't simply diffuse through the membrane so it needs the help of a carrier protein to get it across the membrane so just to review it small molecules like oxygen carbon dioxide water they can diffuse through the membrane for what is a little bit difficult big molecules like glucose big polar molecules they can't diffuse through the cell and ions like sodium potassium they can't diffuse across the membrane without the help of a protein now there's one more thing that we need to talk about regarding the cell membrane another important and that is cholesterol which is right here now cholesterol has a polar region and a nonpolar region the circle in blue is the hydroxyl group of the cholesterol molecule and the hydroxyl group is polar because of hydrogen bonding it's a very attracted to water and so it's gonna be facing outside of the cellular membrane now the fourth fused rings of cholesterol and that's the nonpolar region the hydrophobic region and so that's going to be pointing towards the interior of the membrane now the function of cholesterol in the membrane is very important cholesterol acts as a buffer it maintains the fluidity of the membrane here's a question for you if you increase the temperature what happens to the membrane will it become more fluid or less fluid will the phospholipids will they move apart from each other or will they move closer to each other now let's think of water at room temperature water is fluid if you decrease the temperature let's say if you put it in a freezer it's gonna turn to ice it's not gonna be fluid anymore so whenever you increase the temperature you increase the fluidity of a material now as you increase the temperature of the cellular membrane the phospholipids will move apart from each other and so they will become more fluid cholesterol it functions to maintain a fluid e so it's going to try to decrease the fluidity and so what it does is it kind of prevents the phospholipids from moving apart from each other so that the cell membrane just doesn't dissolve now if we decrease the temperature the fluidity of the membrane will decrease it will become more rigid cholesterol will act to prevent that is going to try to increase the fluidity so it acts as a spacer so these phospholipids when the temperature goes down they want to get closer and so what happens is cholesterol prevents them from getting too close so whenever the fluidity goes up less or tries to bring it down when the fluidity goes down cholesterol tries to bring it up so it maintains the fluidity of the cell so it's another example of homeostasis or equilibrium so that's the function of cholesterol in the cell membrane now let's work on some practice problems just to review some of the things that we covered early in this video number one which of the following statements is not true concerning phospholipids would you say a phospholipids are amphipathic and B phospholipids contain a hydrophilic head see details of a phospholipid point toward the interior of the cellular membrane d phospholipids are the major components of the cell membrane bilayer or e phospholipids contain a phosphate group 3 fatty acid tails and the glycerol molecule so which of these statements is not true or which one is false so let's go through each one this is a true statement phospholipids are amphipathic they contain a hydrophilic polar head and a tails are hydrophobic so answer choice a is the true statement B phospholipids contain a hydrophilic head that is also true as you can see that here and 4c the tails of a phospholipid point toward the interior of the cellular membrane that is also true the membrane looks like this and as you can see their tails are definitely in the interior of the membrane now for answer choice D phospholipids are the major components of the cell membrane bilayer that is definitely a true statement the only thing that's false is e phospholipids do contain a phosphate group and they contain a glycerol molecule but they don't have three fatty acid tails they only have two and so that's why e is not true number two which of the following particles cannot pass through the cell membrane without the assistance of a transport protein so we're going to start with each one because there can be multiple answers so let's say this is the cell membrane can water pass through the cell membrane what would you say now it's not that easy but because there's a lot of water inside and outside of the cell the human body is mostly composed of water it can fit through it and it's very small so water can pass through the cell membrane so this is not what we're looking for now what about the potassium ion can that pass do it ions are not able to go through the membrane they can't get to this hydrophobic region so B is one of the answers that were looking for nonpolar molecules like o - this can easily diffuse in the cell membrane and carbon dioxide which is another nonpolar molecule that can that can easily diffuse out of the membrane out of the cell into the extracellular fluid so we eliminate answer choice C and D now glucose glucose can't diffuse through the membrane without the assistance of a transport protein so glucose it needs a carrier protein to get through the membrane so II would also be in the answer so it's both B and E ions and big polar molecules like glucose and they need a transport protein to pass through the membrane number three which of the following proteins span across the entire cell membrane is it a surface proteins B the globular proteins C transmembrane proteins D integral proteins or e carrier proteins what would you say so let's say this is the cell membrane so this would be a surface protein this would be a globular protein and it's also a peripheral protein because it sticks out of the membrane but doesn't pass through it this would be an integral protein and this would be a transmembrane protein the best answer is the transmembrane protein this it spans across the entire cell membrane the integral protein it's simply embedded within the cell membrane now keep in mind all transmembrane proteins are integral proteins but not all integral proteins are transmembrane proteins and carrier proteins as we mention in the video they simply carry stuff across the cell membrane so this isn't really not the best description of a transmembrane protein they could be transferring proteins they could be integral proteins but this answer is the best answer number four which of the following molecules act as a fluidity buffer in the cellular membrane is it cholesterol aquaporins ion channels glycoproteins or glycol lipids it's not going to be aquaporins keep in mind these are proteins that can carry water across the membrane it's not going to be ion channels ion channels are protein channels that carry ions like potassium and sodium across the cell membrane and it's not going to be glycoproteins so these exists on the surface of the cell and its not going to be glycol lipids the answer is cholesterol so keep in mind as the temperature goes up the fluidity of the membrane goes up the phospholipids move apart but cholesterol kind of anchors the phospholipids together so prevents them from moving apart thus maintaining the fluidity so whenever the temperature goes up cholesterol tries to decrease the fluidity of the membrane under colder conditions the membrane becomes more rigid cholesterol excessive spacer increase in the fluidity of the membrane so cholesterol maintains the fluidity of the membrane now here's another question field number five which of the following can increase the fluidity of the cellular membrane so number one we've already covered this we know that increase in and the temperature will increase the fluidity of the membrane so number one is a true statement what about number two increase in the number of saturated phospholipids will that increase or decrease the fluidity of the cellular membrane well let's talk about saturated fatty acids a saturated fatty acid if you recall has no double bonds and these tend to be solid at room temperature now an unsaturated fatty acid they do carry double bonds and this creates a kink in the structure so these type of fatty acids tend to be liquid or oils at room temperature so you need to understand that saturated fatty acids and saturated phospholipids they tend to be more rigid whereas the unsaturated phospholipids will have more fluidity they're going to be more liquid so the correct answer will be increase in the number of unsaturated phosphorus excuse me increase in number of unsaturated phospholipids that's going to increase the fluidity if you increase the number of saturated phospholipids that will decrease the fluidity so number two is false the answer is going to be 1 & 3 which is answer choice B so this will be an example of a saturated phospholipid because both of the fatty acids they're straight this is an example of an unsaturated phospholipid as you can see one of the fatty acid chains has a kink in the structure which means it has a double bond so if you have more of these phospholipids the membrane is going to be more fluid phospholipids of this nature will create a membrane that's more rigid and less fluid now let's work on some matching problems feel free to pause the video and work out these questions for the sake of a review so let's go ahead and begin number one so this allows some molecules to pass through while preventing others from doing so so which word best describes that sentence so the answer for this would be a semi permeable membrane it allows certain molecules to pass through the membrane while preventing others from doing so number two so which word goes with this sentence it allows water to pass through the membrane efficiently so this would be an aquaporin number three this explains how phospholipids and proteins are free to move in the cell membrane so this is gonna be the fluid mosaic model so we're gonna put letter I for number three number four this allows particles like potassium and sodium ions to pass through the membrane so this is gonna be I on channels so let's put G for number four number five this maintains the fluidity of the cell membrane so this is going to be cholesterol so let's put B for five number six and this molecule plays this should be plays a role in cell communication self-recognition in immune system will molecules that this is gonna be the glycoproteins so that's a D number seven an Fe Pathak molecule that makes up the cell membrane bilayer which one is that so the answer is going to be L phospholipids are ant V Pathak they contain hydrophobic and hydrophilic parts to themselves and they make up the phospholipid bilayer of the cell membrane number eight so this plays a role in cell signaling I said that wrong cell signaling and tissue recognition so this is going to be the glycol lipids and number nine this macro molecule is completely embedded within the lipid layer I mean the lipid bilayer my words is just not coming out right today so this is going to be the integral proteins they're completely integrated in the lipid bilayer number ten this molecule completely spans through the membrane so this is going to be the transmembrane protein so that's C number eleven this component transports molecules across the membrane so that's going to be the carrier protein that's H and twelve this molecule lives on the exterior of the cell membrane which is F the peripheral proteins surface proteins also lie on the exterior of the cell membrane but the peripheral proteins part of it is inside the membrane and part of it is outside of the membrane but it doesn't span completely through the membrane so that's basically it for this video that's an introduction into the cell membrane thanks again for watching and if you liked it don't forget to subscribe to this channel

Channel: The Organic Chemistry Tutor

Views: 35,166

Rating: 4.949091 out of 5

Keywords: cell membrane

Id: AsffT7XIXbA

Length: 27min 36sec (1656 seconds)

Published: Tue Oct 08 2019