Transcript for:
Week 6: The Cell Membrane

the cell membrane the cell membrane is a plasma membrane that makes up the outside border of the cell when looking at a cell under a microscope it appears as a pair of thick dark parallel lines um you can see them under most electron microscopes it's pretty easy the membrane has both intracellular and extracellular faces meaning it has a side that is inside the cell and the other side is outside of the cell and the functions of the cell membrane include setting the cell boundaries so separating the cell from its outside environment governing interactions from the cell and other cell so regulating how the cell interacts with other cells around it and then it controls passage of things in and out of the cell it has a selectively semi- permeable membrane meaning it's very selective on What it lets in and out and semi-permeable means that only some things can penetrate through the membrane so its main function is keeping things out that should be out and keeping things in that should stay inside of the cell what is the cell membrane made of so last week when we covered macro molecules we talked about phospholipids briefly and they are the macromolecules that are composed of phosphates and lipids um now 98% of the membrane molecules are lipids and then 75% of the membrane lipids are phospholipids so 75% of that 98% of the whole membrane are phospholipids so they are amphipathic molecules and they're arranged in a Bayer so amphipathic just means that one end of it is hydrophilic and the other end is hydrophobic and hydrophilic means water loving hydrophobic means water hating so one end of a phospholipid enjoys water and loves water will dissolve in water the other end will repel against it not dissolve in it because it hates it so if you think about what doesn't like water fats don't like water so the fatty end of the phospholipid is the hydrophobic end and the phosphate end is the hydrophilic end so the hydrophilic phosphate head faces water on each side of the membrane so if you look at this diagram the pink part is the phosphate end and that's hydrophilic the hydrophobic tails are directed towards the center avoiding water so they align this way because the Tails want to be away from water and there is water inside and outside of the cell so in order to get away from the water the Tails turn inward towards each other so the water stays up near the heads on both the inside and the outside of the cell membrane that's how it arranges in a by layer the Tails want to be near other Tails because it keeps them away from water so these things drift laterally keeping the me mebrane fluid meaning they always move they're not tied down to each other in any way shape or form so it is very fluid it's referred to as a fluid mosaic the membrane can jiggle and wiggle and move and separate as it needs to because nothing is anchored together so we talked about how 75% of the 98% of the membrane is phospholipids but 98% of that entire membrane is made of lipids so what are the other lipids well 20% are cholesterol so these are things that hold phospholipids still and they can stiffen the membrane so remember that the things are not anchored together those phospho lipids are not tied together and anchored down so a cholesterol can kind of act as like a sticky substance to hold them together and stiffen the membrane if it needs to but it's not like cement it can move still glycolipids these are sugar fats and these make up the other 5% of the membrane fats so phospholipids these are phospholipids with short carbohydrate chains on the extracellular face or the outside of the cell and they contribute to the glycocalix um which makes a coating on the whole cell surface so a glycolipid is going to be like these little stem things here sticking out it's a carbohydrate chain on the outside of the cell surface and then the cholesterols are the things that hold the phospholipids kind of together in addition to fats cell membranes also have proteins so proteins only make up about 2% of the molecules in the cell membrane but they count for about half of the weight because they're really big and bulky so you can have integral proteins which penetrate the membrane and integral means they integrate right so something that integrates kind of goes into it so integral protein go inside of the cell membrane um they're transmembrane proteins that pass completely through so you can enter this protein from the inside or the outside of the cell it goes all the way through the cell membrane like a channel they have a hydrophilic region which contacts the cytoplasm or the extracellular fluid and they have a hydrophobic regions which pass through the lipid of the membrane so the ends of these are hydrophilic just like the ends of the phospholipids the phosphate heads the outside and then the middle section is hydrophobic just like the Tails of the phospholipids some of these drift into the membranes others can be anchored into the cytoskeleton it just depends on the type of membrane sometimes they can float around and move sometimes they can fall in sometimes they're stuck in place because they're anchored it just depends then you have peripheral proteins and if you think about what the word peripheral means it means on the sides right so peripheral protein are ones that are stuck to either side of the membrane and it does not go through the actual membrane so they adhere to one face of the membrane either the intracellular side or the extracellular side and they're usually tied down to the cytoskeleton and these ones don't fall into the membrane or move they're pretty anchored in place so there are different types of membrane proteins first we have receptors and these respond by binding to chemical signals so their whole job is to sit on the side and wait for a chemical signal or hormone to be sent so it can grab it and read it and then the cell can respond the second messenger systems these communicate with cells receiving chemical messages um so these communicate with the cell when it receives a message or it communicates with another cell when it receives a message it's just a messenger system there are enzymes these are things that speed up or catalyze reactions any kind of chemical reaction can sped up with a specific enzyme and it's called a catalyst it just means to speed up um in these things speed up messenger systems or processes in the cell when it receives a signal to do whatever the signal tells it to do there are channel proteins and these are the things that allow hydrophilic solutes and water to pass through the membrane so channel proteins go through the membrane and allow things to go in and out it acts just like a channel so things can enter and exit the cell some channel proteins stay open all the time some are gated and have to be open by certain voltages or certain electrolytes or ions um some are opened by chemical Messengers it just depends on the type of channel so there are liand gated channels which are open by chemicals there are voltage gated channels which are opened by electrical charges and there are mechanically gated channels which respond to physical stress on the cell so if the cell is getting squished or heated up or something like that those can be opened mechanically so membrane channels can either be opened or gated and those are the three types of gates these gated channels are crucial to nerve and muscle function specifically your muscle impulses your responses to stimuli when you're hurt or burned or anything like that and your heart is ability to contract um those are all things that are controlled by these channels you can have carrier proteins these bind to Sol es or solid things either inside or outside of the cell and they move them across the membrane so a carrier protein can bind with something outside of the cell and move it through the membrane to the inside of the cell or it can do the opposite and bind with something inside of the cell and move it through the protein to push it out if it doesn't want it in the cell they just carry things that's why they're called carrier proteins so these things can be operated by pumps um which push things in and out of the cell um there there are cell identity markers and these are glycoproteins acting as an identification tag so some cells have glycoproteins on it that give it identity of what the cell is so there's a little marker on the cell that says hey this is the kind of cell that I am and that's a glycoprotein and then there are cell adhesion molecules these mechanically link cells to extracellular material so they could link a cell to another cell or to a certain surface so it stays in that area because it might be say it's a um immunity cell it's trying to eat bacteria on a wound on the side of the liver well it can adhere itself to the side of the liver so it stays in that area and continuously eat that bacteria it doesn't have to keep trying to get back to the area it can adhere itself so it stays making its job easier so functions of these membrane proteins we have a ton of them right so the functions there's a pretty wide variety of functions right so you have receptors that receive m mesages you have second messenger systems that receive interpret or send messages you have enzymes that speed things up channels that move things carriers that carry things identity markers that identify things and then adhesion molecules that stick things together so these are all different functions of the different proteins that you can find in the cell membrane here's a brief graphic on the different proteins and their functions so receptors bind to chemical signals and receive the messages from them enzymes U speed up chemical reactions there's channels which allow things to pass through it just like a channel like think of a channel um like on the water it allows passage between waterways right so things just pass through a channel gated channel it's the same thing but it's controlled by some kind of locking mechanism whether it's chemical Messengers voltages or mechanical stimuli it's a gated Channel meaning it has to be opened when it's when it's supposed to be used there's cell identity markers which identify cells so our body can identify cells as our own our foreign Invaders is it a good cell is it a bad cell the identity marker is really important for immunity and then there's cell adhesion molecules which just allow the cell to attach itself to something it needs to stick to does it need to stick to the liver does it need to stick to another cell whatever it need to stick to those adhesion molecules are the things that allow it to grab onto other things so one of the most important if not the most important functions of the cell membrane is transport so the plasma membrane and organel membranes so the membranes that surround certain cell organel allow things to pass through only when they are supposed to so it's like the gatekeeper of the cell does this thing need to come in no the cell membr is not going to let it in does this thing need to go out yes so the cell membran is G the cell membrane is going to allow it to go out so it's the gatekeeper of what comes and goes from the cell some other organel in the cell have their own little organel membranes very similar to the cell membrane like the nucleus the nucleus is very selective on What it lets in and out it has a membrane and it works very similarly to the entire cell membrane but when we're talking about the cell membrane we're talking about the large membrane around the whole cell so it allows certain things in and out um and it does this by passive transport and active transport so a passive transport is a transport that requires no ATP or no energy it can just happen without the cell having to work and this is usually done through filtration diffusion or osmosis active transport is a type of moving of things that requires energy the cell has to put in energy it has to do work um there is Carrier mediated mechanisms which a protein assists the cell in moving things across the membrane and sometimes they require energy and sometimes they don't it just depends on which type is happening so first we're going to talk about passive transport which is that way of transporting things that doesn't require any energy so the way this happens is through the use of concentration gradients so a gradient is just a measurement of how much of something is in one area compared to another area so a concentration gradient is an area that has a different concentration in one area from the next so there's a different number or different concentration of things from one area to the next that is a gradient there's a different amount so a concentration gradient allows things to move from high concentration to low concentration without the use of energy things will naturally move from high to low so um just think about it like a hill if you're at the top of the hill and you need to get down to the hill you can just lay and roll right gravity is going to help you you're going to move from high to low very very easily with very little work and that's how things work chemically as well high to low concentration things are going to move from a high concentrated area to a low concentrated area with no energy easily and automatically they're going to continue to move from high to low until both areas are balanced so think about a room full of people you have two rooms in your house right the first room has 50 people in it it's crowded and full and it's way too tight to move around in there the next room over has like three people in it naturally people are going to start moving to the less crowded room right people are going to continue to move until the room becomes about as crowded as the other room and then movement's probably going to slow down that's how it works in the cell the chemicals or the solutes or whatever is in that concentration that we're talking about it's going to move from the high area to the lower area until both areas become level and then it's going to stop moving okay and that's no energy and that's either through diffusion or osmosis depending on what is moving so this is a chemical driving force that moves things from higher to lower concentrations and it's just a chemical property and it requires no energy and it happens from inside to outside of the cell and in different areas of the body so let's talk about these gradients in the different types of transport so let's talk about filtration first so particles are pushed through a membrane by physical pressure okay so the physical pressure is usually flowing of something blood water fluids something is being pushed through and then um it's going to filter things out through a membrane just because it's being pushed through that area this requires no energy it is passive transport okay it goes down the concentration gradient because remember passive is always high to low so you're going to go from high to low which is down the gradient some examples of this are filtering water in small solutes or particles through gaps in your capillary walls which are some of your small blood vessels this allows water and nutrients to be delivered to the tissues and then allows waste to go through the capillaries and go to the kidneys to be removed from your body so if you look at this capillary here the cells are on the outside okay and they have membranes so as the blood is Flowing to this capillary if there is a high level or a high concentration of let's say sodium inside that blood and there's a low concentration on the other side of the cell then that sodium is going to easily move through that cell membrane from the blood area on the inside to the outside where the concentration is less it's going to happily just move right through it by filtration okay it's filtration because it's being pushed with pressure so anywhere that anything flows is going to be a filtration mechanism the kidneys most blood vessels and the liver as well that's filtration so a simple diffusion is the movement of particles from high to low concentration okay and it's just due to a difference in concentration there isn't anything flowing or physically pushing it it's just that these particles are high on area and low in one area and they want to balance themselves out they're always going to try to balance and make equilibrium happen or a nice happy balance on both sides so um there is movement in molecules so all molecules move and as they move they bounce off each other um and then they start spreading out until they get to the area of lower concentration substances are always going to go down the concentration gradient um it does not have to have a membrane to make diffusion happen but if there is a membrane and the concentration is different from one side to the other diffusion will happen through it as long as the membrane allows the thing to penetrate it so if the membrane does not allow magnesium to go through it then magnesium is not going to diffuse through it because it's not allowed to go through the membrane because remember that membrane is selectively permeable meaning it can pick and choose what enters or exits right so as long as the membrane lets these solute pass through they will diffuse from high to low and they do not have to have a membrane to diffuse from high to low so if we look at this diagram here okay so it's in thirds the first third all these little solutes are blue hexagons are they hexagons one two three four five yeah they're hexagons so all these little blue hexagons are on the extracellular side up here there is none on the Bott or the cytoplasm okay extracellular means outside of cell cytoplasm is the gooey inside of the cell so all of these solutes are outside of the cell there's not really any inside the cell right so just naturally if this membrane lets these solutes pass through they will naturally flow from the higher concentrated area to the lower concentrated area so they will naturally flow from the extracellular fluid down through the plasma plasma membrane and into the cell okay so the middle section shows how they're starting to flow they're happily flowing doesn't require any energy it's simple diffusion okay they're going to keep flowing until equilibrium is met and if you look at this last one there's the same amount on the outside and the inside now because equilibrium has been met once equilibrium has been met there is no concentration gradient anymore there is no high and low it's equal so things will stop flowing and that is simple diffusion so how can we speed up and slow down diffusion there are a few different factors that will affect the diffusion rate through a membrane one is temperature temperature always speeds up any kind of reaction or movement just think of everybody sitting in the classroom you're sitting in the classroom you're still it's fine if I light the classroom on fire is everybody going to move faster yes most likely everyone's going to get up and run right so when you heat any kind of molecules they move quicker always so if we heat up a cell or we heat up the extracellular fluid or anything like that it's going to make things move quicker to the membrane it's going to make diffusion happen quicker U molecular weight is going to slow down diffusion because heavier molecules weigh more and they're harder to transport so just in general they take longer the the proteins have to work harder or they have to squeeze through the membrane they're too big so they're going to slow everything down smaller particles are going to travel much faster steepness of the concentration gradient so the more steep the gradient is the faster so if there is a hundred things outside of the cell and one thing inside it's a huge difference in concentration right they're going to move really really fast as you start approaching equilibrium the movement is going to slow down the more equal it gets the less movement so if you want to increase something deepen that gradient make it more steep if you want to slow something down bring the gradient closer together membrane surface area is going to increase the rate because the more area for something to move across the quicker things are going to move so if you were to take let's say a bottle like a soda bottle and poke one hole in it and throw it in a a bucket of water it's going to take a long time for the water to fill that bottle right really really slow if any gets in there it's going to take forever but if you poke a hundred holes in that bottle and then throw it in a bucket of water a whole bunch more water is going to go in and it's because there's way more surface area that the water can enter has way more holes it can go through all of them so increasing surface area on something is always going to increase how fast it can do something whether it's diffusion or filtration more surface area allows more of whatever process to happen and this will be really important when we talk about um like the intestines and the lungs and Anatomy too surface area is really really important in those organs and then membrane per membrane permeability will speed up the reactions or the diffusions because if the membrane is allowing more things to pass through or it's more permeable obviously more things are going to pass through right the less permeable the membrane is the less things are going to go through it so the slower things are going to move so all of these things can either slow down or speed up the rate of diffusion in a cell membrane now let's talk about osmosis so osmosis is exactly the same as diffusion in all aspects except it's only water nothing else will move through diff through osmosis except water it is diffusion of water and only water you can't have sugar salt magnesium nothing else in it just water so if there are any particles or solutes in it it's not osmosis it's diffusion okay so it's diffusion of water water flows through the membrane and it it flows from areas that are high to low but not in water concentration so it's going to move down the concentration gradient but it's the concentration of the solutes or particles in the water so it's kind of backwards so let's think about uh you have this box okay so this picture right here you have water on one side and sugar solution on the other side okay the sugar solution is highly highly concentrated in sugar solution because if you look there's like 20 sugar Solutions and there's only like five or six Waters right concentration of sugar is really high on that side especially compared to the other side where there is none so the sugar is not going to move okay but the water is going to move to try and dilute lute that sugar solution down to make it the same concentration as the pure water so water is going to rush into the area of high concentration to attempt and dilute it okay that is osmosis so it's not moving from high to low water concentration it's going to move from high to low something else concentration in an attempt to dilute it if that makes sense so this is crucial for IV fluids um it's crucial for maintaining osmotic balance um things that can cause diarrhea constipation edema and things that the dehydration that are caused by those um this is how we rebalance our fluids when that happens um water can diffuse through the phospholipid by layers but osmosis is enhanced by these things called aquaporins so aquaporins are channel proteins that are just Channel like Channel openings for water to pass through so they're channel proteins that are open all the time and only water can go through through so they're selective in the fact that they don't let anything else put water in in cells can speed up osmosis by installing more aquap porns in their membrane so let's say you're severely severely dehydrated your cells might start making more aquap porns really quickly and sticking them in the membrane that way it can allow for more water to enter um so it can rehydrate faster so osmosis is just water and it's going to go from high to low concentration it's going to be passive meaning no energy and remember it's moving in an attempt to dilute whatever the solution is in the area it's not moving in an attempt to add more water because there's no water or the water is less it's trying to dilute the concentration of whatever is in the area it's moving to so if you have a cell that is really really really salty like high sodium content inside of it compared to the outside environment water is going to rush into that cell to an attempt to dilute that sodium down to make it match the outside environment so it might be really hard to move sodium out of the cell or it might be slow to move sodium out of the cell or maybe the cell can't move the sodium out but it can always move water in so it's going to move water in like crazy and try and dilute that sodium down that's osmosis just water movement from high to low concentration and it is passive transport so the cell doesn't have to use energy it's just a chemical process that occurs naturally just like diffusion and filtration on the topic of Osmosis let's talk about reverse osmosis and osmotic pressure so osmotic pressure is just how much pressure is required to move water through osmosis so when a solution is really highly concentrated with a solute it produces pressure so let's say we have um a ton of sugar on one side of this barrier and like no sugar on the other side the high level of sugar is going to create like a pulling power to pull water in okay so more solute or more concentration equals more pulling power because there's more osmotic pressure the higher the pressure the more water is going to pull in and the faster as that solute starts becoming diluted by the entering water osmotic pressure is going to slowly drop because it's less concentration right it's being diluted so there's less solute compared to water right so as time goes on and water comes in eventually the pressure is going to drop so much that it stops osmosis that's osmotic pressure it's just the amount of pressure created by the level of solute to pull water in what is reverse osmosis so I'm sure everybody's heard of this and it's like a fancy way of filtering water so this is a way of applying mechanical osmotic pressure um to override the regular osmotic pressure and push water backwards so typically if you look at this diagram the first one is regular osmosis this green side has all these solutes okay and then the water side this blue side has just a few solutes so water is going to move to the area from high to low concentration to dilute it okay so water is going to move in to the high concent ation and dilute right it's always going to go to the high concentration water is going to flow and dilute okay on the reverse osmosis it's going to push pressure on this highly highly concentrated side to get water to move the opposite direction let's move it the other way push it through this membrane the water goes to the membrane but all these little particles over here do not so it in turn filters the water right and it's reverse osmosis because the water naturally wants to move the other direction it needs to get over to this green side to dilute right it needs to go from these over here with it's really really low it needs to go over here and make this low as well and get that equilibrium so this applied pressure pushes water through backwards thus filtering the water from the solute and that's just a way that we can filter water that doesn't happen in our body but we can use it to filter water and other things like that with mechanical pressure all right so let's talk about osmolarity so osmolarity is the number of osmoles per liter of solution so this Compares water to solutes so water to whatever particles are in it okay so a solution is anything that's like dissolved in water so um osmolarity could compare the sugar in water concentration of sugar water okay it can compare the salt and the water concentration in salt water so it just Compares whatever is in the water to the amount of water okay it shows us how much water is in a solution um body fluids contain a mix of many many chemicals and osmolarity is the total osmotic concentration of all the solutes so blood and plasma tissue fluid intracellular fluid all these things have an osmolarity that is really important to maintaining proper bodily function in one oos moo is one mole of dissolved particles so this takes into account whether the solute ionizes or breaks up into water or it does not so um certain body fluids have certain osmolarities that they need to maintain and when the osmolarities are off it causes a lot of problems in our body so um something that we can talk about is we can talk about blood so your blood should have a certain amount of you know ions in it like calcium magnesium sodium it should have a certain amount if we add too much then all the marity gets off because now we have too many many salt particles in the blood in comparison to water and usually osmolarity when it gets too high it makes things really really thick and when it gets too low it makes things really thin because there's too many solutes or not enough so think about making Koolaid so you put a packet of Kool-Aid in however many cups of water let's say eight cups of water one packet of Kool-Aid you're supposed to put one cup of sugar what if you put 10 cups of sugar that concentration of sugar to water is going to be crazy high right way too much sugar not enough water so your osmolarity of sugar is going to be way high and it's going to make it really really thick so osmolarity is just how much solute is in your solution or particles compared to water tenacity of a cell so the definition of tenacity is the ability of a surrounding solution to affect fluid volume inside of a cell um and it depends on the concentration of solutes and it's the non-permeating solut so the solutes that can't move through the cell and it's the concentration either inside or outside of the cell a cell can either be hyper ISO or hypotonic and this is just a cell's tone so by cells tone I mean is the cell tone is it firm is it really really big and Bloated or is it shriveled just think about like muscle tone do you have big strong like bounding muscles are they okay and kind of firm or are they really really weak and triing so cells can be tone like that and it is all regulated by fluid volume and the fluids are moved by concentration gradients hypotonic Solutions so these type of solutions cause the cell to swell and absorb water and remember when we're talking about hypotonic Solutions we're talking about the solution not the cell itself okay so a hypotonic solution is going to be a solution that has less concentrate of something in it than the cell so we have a cell it's a regular let's say you have a skin cell it has some salt in it some magnesium in it whatever it's got sodium magnesium calcium whatever is inside of it you throw it in this water that has absolutely nothing in it right the water is going to move into the cell and attempt to dilute the cell to match the solution osmosis water is going to move in okay the salt and the magnesium and what whatever is inside of that cell are not going to move out because we're talking about non-permeating things right now so they can't move out of the cell the cell can't get rid of them but the cell can try and dilute it so water is going to move in through osmosis and attempt to dilute whatever is inside the cell make it match that solution and and because this happens it's going to increase the fluid volume inside the cell the cells are going to swell some of them might even burst depending on how much water flows into them um so this happens because the solution has a low lower concentration of solutes than the inside of the cell the concentration is lower inside than outside okay the fluid's going to move in and it's going to cause the cells to probably burst this happens a lot in distilled water you put cells in distilled water the cells have way way more concentration of pretty much everything in them than the water so water will move in okay so hypo means too low are not enough so the solution does not have enough concentration of solutes the solution is too low cell is going to swell hypertonic is the complete opposite so there's too much concentration in that solution so let's say we throw a cell in a hyperonic solution like salt water there's a ton of salt in that solution and not as much in the cell water is going to move out of the cell in an attempt to dilute that solution down and it's going to cause the cell to shrivel up or Shrink okay it's going to look all shriveled and dried up so this is because the the solution has a higher concentration water wants to dilute it's going to move through osmosis just like in the hypotonic um it's just going the opposite direction so the different solutions can cause water to move in different directions so what happens if there is no difference so if there is no difference in concentration from inside the cell and in the solution it's considered an isotonic solution and ISO just means the same like is isometric means the same measurement same shape isotonic just means the same tone or the same amount of solutes so in an isotonic solution equilibrium has already been met so nothing is going to move because remember things move to make things balanced right it's already balanced why do we need to move we don't so no movement happens the cells don't shrivel or swell water doesn't move inside or outside everything just kind of stays where it's at the cell stays inside the cell and the water in the solution stays outside of the cell nothing happens everything is happy this is really important when we're giving IV fluids we want to make sure that we're not giving IV fluids that are hyper or hypotonic unless we need them because it can cause a lot of problems in the cells it's nice to give a nice isotonic solution such as normal saline that way the body doesn't you know pull water in or push water out and attempt to regain balance when we put these crazy Solutions in our body carrier mediated diffusion is a passive transport that occurs because a carrier is facilitating that diffusion so the cell isn't actually putting out the energy to make the work happen because a carrier protein is picking up the particle that needs to be moved and is actually moving it or is pushing it through a channel so proteins are transported in the membrane either in or out of the cell um cell membrane does not allow these solutes to pass because they're too big or too polar so if the cell membrane doesn't allow things to pass through it a carrier protein can go grab it and pull it through or open to allow it to go through so it can make it a bigger channel for these solutes to go through if the cell membrane does not allow it to go through um the transport proteins are specific for this particular solute so specific proteins will allow passage or move specific things not all proteins move all solutes and there are three types um there's facilitated diffusion there's primary active transport and secondary active transport those are all types of carrier mediated diffusion and the proteins can act as a channel to allow specific solutes to enter and exit the cell so either they can open and close to allow one thing one solute at a time to go through they can grab and pull them through or they can act as a channel where things can slide through carrier mediated diffusion has specificity and saturation can change the rate at which it happens so in the carrier mediated diffusion this example we have a liated channel so the channel is going to be something that opens and allows things to pass through just like a channel for boats so in this case we have these gated channels and a solute or a liand will come along and if it's the the right one to go through the channel it will bind to the site on the channel the receptor site and cause the channel to open when that channel opens these solutes can move through when the solutes are done moving through the solute the Lian will unbind and it will close a channel only specific lians can open these channels they are like keys this key opens this channel this key might not open the next channel so it's very specific to each Channel and each liand when the solutes travel through these channels they are unchanged nothing happens to them they just float through and they come out on either side normal they don't go through any chemical or physical changes so when the saturation of a solute Rises they're going to transport faster because concentration gradient is a lot higher if we have the outside of the cell and we add a whole bunch more solute it's going to want to move into the cell faster because remember increasing the concentration of anything increase the rate of diffusion so this will happen until it gets to a transport maximum the transport maximum is when all of the gates are full and the carriers are all busy moving solute they can't move anymore so it'll speed up until the carriers are too occupied moving their solutes where they can't pick up extra solutes that is the transport maximum all the carriers are occupied and there's none running around loose to pick up any extra solutes that will affect the rate of carrier mediated diffusion so there are three main kinds of carrier proteins there are uniport sort and antiport and and their names kind of tell you what their function is so a uniport protein carrier or a uniport carrier protein will carry one type of solute that's why it's called a uni Port one it has one port okay an example this is a calcium pump it only carries calcium a sort will carry two or more solutes at the same time in the same direction so it's like car pooling if one's going one way and another one needs to go the same way a Sim Port carrier can grab both of them and carry them through okay so Sim means together like working together so a Sim Port it works together to carry two an antiport can carry two or more solutes in opposite direction so anti means like against right so an antiport it can carry two solutes in opposite directions so one could be going into the cell and one could be going out out of the cell all at the same time okay so an example of that is a sodium potassium pump when the sodium goes out the potassium comes in they go opposite directions that's an antiport carrier protein and if you look at this picture the first the for this left one a is a uni Port you can see only one thing is going through in One Direction B is Sim Port it's carrying two it's carrying a substrate and this proton they're going the same direction but it is carrying two things and then C is carrying two different things in different directions so that would be an Port membrane potential is the voltage across a membrane so the electrical charge across the membrane of a cell the voltage is created by differences in the distribution of positive or negative ions inside and outside of the cell or across that membrane the inside of the cell is typically negative in charge compared to the outside so there are more negative ions inside of the cell and more positive ions outside of the cell and this favors a passive transport of positive or cat ions into the cell and an i out of the cell so remember they're always going to move with the gradient so if the inside of the cell is more negatively charged the positive ions are going to want to move into it so they can neutralize that charge and if the outside's more positive the negative ions are going to want to move out to neutralize that positive charge they're always going to move from high to low so high concentration to low concentration if it's highly concentrated inside in positive ions or negative ions whichever one's highly concentrated they're going to move to the area of lower concentration and resting membrane potential is just that membrane potential when the cell is at rest when it's doing nothing and electrochemical gradient is a gradient that is created by two different forces one's electrical and one's chemical so in this case the electrical gradient is created by the membrane's potential the voltage of the cell membrane and the chemical gradient is created by the concentration of ions inside and outside of the cell and remember everything's always everything is always going to diffuse down its concent concentration gradient as long as it is permeable and can pass through that membrane so if you have something that's really really highly concentrated outside it's going to want to go to the inside of the cell where there's a lower concentration but these two things together create an electrochemical gradient and it just means it's a gradient of both chemical concentration and electricity so the amounts of ions inside and out of the cell directly affect the voltage inside and out of the cell if we have 100 positive potassium ions inside of a cell it's going to favor in the electrical way of a positive voltage right because they are positive ions or catons if we have way less outside of the cell it's going to favor more negatively outside the cell compared to inside of the cell so these two things together create the electrochemical gradient one type of cellular transport is co co transport and this includes both sort and antiport and this just means that two things are moving through the cell in either in or out um and one of them is going with the concentration gradient and the other one is going against the concentration gradient an example of Cod transport let's talk about plants first so plants use these things called proton pumps okay the proton pump works against the concentration gradient and pushes hydrogen out where it's way highly concentrated remember things naturally want to move from high to low concentration so if you look at this illustration you can see there's like one hydrogen inside and there's like six outside right the hydrogen doesn't want to move outside because it's too high out here it wants to stay in so the cell has to actively push it out or force it out by active transport going against the gradient when that sodium gets out it's like wait it's too concentrated out here I want to come right back in so that sodium gets out there and decides to come right back in and it diffuses back across the membrane this diffusion of sodium causes enough change in the membrane where something else can go through and diffuse with it and in this case it's sucrose so by pushing out the hydrogen we create basically a highway back into the cell for the hydrogen and the sucrose kind of jumps on that Highway and comes in with it and this is how plants push sucrose into their veins to be transported around the plant they use a proton pump so something is going against the gradient and because that thing went against against the gradient it's creating basically a new transport for something to go with the gradients another example of Co transport but in animal cells is the coupling of sodium and glucose transport so sodium potassium pumps actively push sodium out of the cell against the concentration gradient anything that is active requires energy meaning it's going to go against the gradient so the cell is pushing sodium out where it's a higher concentration it forces it out once the sodium gets out there the concentration is really high out there so the sodium wants to come back in right it's going to want to flow back to the lower gradient so the lower concentration gradient so the sodium it's going to get forced out of the cell but it's going to turn around and try and come right back in when the sodium comes back in it creates enough change to allow something else to come back in with it in this case it is glucose so the sodium comes out of the cell by force or active transport it comes back in by passive transport and simultaneously glucose comes in as well because this generates enough electrical change to allow the glucose to enter this is the process the animal cells use co-transport forcefully push out the sodium it wants to come right back in but glucose follows in with it and normally you can see this in the body or in animals because sodium is reabsorbed in the colon to maintain a constant level so we might push sodium out of the food but it can be reabsorbed really really fast because the gradient um is in the favor of the reabsorption of the sodium so in facilitated diffusion the carrier moves solutes down a concentration gradient so it's just like diffusion where the concentration is going to be higher either inside or outside the cell and the solutes are going to move from that area of higher concentration to the area of lower concentration that is going to happen passively so no ATP is going to be consumed by the cell the solutes are going to attach to a binding site on the carrier the carrier is going to change shape open up allow for passage of a certain size or certain shaped particle and then it's going to enter it and then the carrier is going to open up again or change shape so it can come out the bottom so if you look at this picture you can see that there is a bunch of these solutes in the extracellular fluid in the ECF so the carrier goes into this or the solute goes into this carrier you can see the carrier has a slot big enough for one solute one particle so it goes in once it gets into the site it will bind at the site which will activate the carrier to change shape or change confirmation it'll cause the carrier to close at the top and open at the bottom then the solute will move out into the cell into the intracellular fluid so this is how facilitated diffusion happens with carriers um and again because it is diffusion it's high concentration to low concentration no energy because we're going down the gradient okay so primary active transport occurs when cells move solute through a membrane against or up the concentration gradient so we're going to be going from a low concentration to a high concentration which is uphill right so it's going to take energy um the carrier is going to consume energy from the cell and some examples of this are calcium pumps um they use ATP when expelling calcium from the cell where it's already more concentrated so there might be less calcium inside the cell than outside the cell but the cell needs to get that calcium out so it's going to have to use energy to push it out because there's no concentration gradient that's going to favor moving it out it's going to favor moving it in um in sodium potassium pumps use energy when expelling sodium and importing potassium so those are those antiport pumps that push one thing one way and the other thing the other way and it's always going to be where one thing is going to be against the concentration gradient if not both things so it has to take energy it's got to consume energy to move things one of the two ways if not both ways so primary active transport things are moving through the membrane against the concentration gradi gradient and they are consuming energy so now we have vesicular transport this is how things move large particles like fluid drops or a lot of molecules at one time through a membrane they move them in bubble like things called vesicles so they have motor proteins that work as little Motors and they are ran by energy so it definitely consumes ATP it is active transport and these things can either go in or out of the cell so they can bubble around a group of items or group of molecules whatever they need and carry it kind of like luggage either into the cell or out of the cell it They're ran by motor proteins that act as little Motors and they have to use energy so by this time we know that cells can both take in things and put out things so let's talk about these processes so the first process is endocytosis and if we break this word down Endo means in or enter site means cell and osis just means condition of so endocytosis breaks down to condition of entering or going into a cell so endocytosis is when cells bring things in and this can happen by phagocytosis pinocytosis or receptor mediated endocytosis so phagocytosis is when cells eat large solid particles okay they can do these by using pseudopods which are those finger-like projections that they can grow when they need them and then get rid of them there are phagosomes which are parts of the cell that are used to ingest things and then macras they also inest large things um cells can also take things in by pinocytosis and this is called or referred to as cell drinking so this is when cells take in liquid molecules um membranes can cave around the liquid and kind of bubble around it and then break off into like a little vesicle um I remember Figo and pinocytosis because penino sounds like penino like wine so it reminds me that it's drinking so penino is wine pinocytosis is drinking the other one is eating it's not drinking it's got to be eating so pinocytosis is drinking and fyos is eating of the cell and then we have receptor mediated endocytosis which which can be taking in anything when it's using receptors so particles bind to specific receptor sites on the membrane and then the membrane kind of bubbles around it and pulls it in if you look at these pictures you can see how the membrane kind of bubbles around and engulfs things like this these are all parts of the membrane's job they just are categorized by the type of thing that they're bringing in or if they're being helped so solids is phagocytosis liquids is pinocytosis and if a receptor is binding to the membrane to like encourage it to take things in or activate the process of taking things in it is receptor mediated endocytosis so here's another visual of receptor mediated endocytosis you can see that the receptors are binding to the membrane um and remember receptors only bind to specific sites not just any receptor can bind to any site they're very specified so this receptor is made to bind to this site so these receptors come in and they bind to the site when they bind to the site they activate the cell's membrane to kind of make like a bubble and start pulling those things in okay it'll continue to pull them in until it kind of makes a vesicle and then it will break off from the membrane and separate itself and that bubble will go into the cell and then the cell can consume it and do whatever it intended to do with it this could be for energy it could be because something needs to come in the cell so it can be modified it could be a virus that the cell is trying to break down a bacteria it could be one of many things um but it will pull it into the cell to do whatever it has intended to do with it so cells bring all these things in with endocytosis but they also need to get things out okay so cells have waste or they have parts of them that are no longer functioning or something has got into the cell that is causing damage to the cell and they need to get it out so the process of getting things out of a cell is exocytosis EXO means to exit site is cell and osis is condition of so when we break down exocytosis we get the condition of exiting or leaving the cell so exocytosis in short is just discharging material from the cell that is no longer wanted or needed so trans cytosis and if you guys remember what trans means it means like through or across or to the side in site means cell and osis is again condition of so transcytosis is transport of material across the cell okay by capturing it on one side and releasing it on the other so instead of going through I mean instead of going around the cell it's going to go through the cell okay so the receptor mediated endocytosis is going to pull this thing in the cell is going to then do exocytosis and push it back out the other side okay so usually the thing will go through unchanged um there's many reasons why it would go through it depends on the type of cell it depends on what what it's trying to accomplish but in this picture you can see we have blood and it's going into the brain so this is probably one of the most simple examples of transcytosis this is going to be the blood brain barrier where in your brain the brain bra fluid and the blood do not mix there is a layer of tissue in between them that separates them so anything that is in the blood that needs to get into the brain is going to have to go through this tissue but again we don't want blood in there so whatever nutrients or whatever proteins whatever needs to get to the to the the brain's fluid is going to go through this through transcytosis it's going to leave the blood enter the tissue and be pushed through by endo and ex exocytosis and out the other side just whatever needs to get through the proteins the nutrients whatever it might be not the actual blood so transcytosis is transporting something through the cell but it's not being eaten or taken in it's literally just going in and coming right back out the other side