Understanding the Cell Membrane: Structure, Function, and Importance

foreign what's up Ninja nerds in this video today we're  going to be talking about the cell membrane before   we get started I really hope that if you guys do  like this video you find a lot of benefit from  

it please support us and one of the best ways  that you really can do that is by hitting that   like button comment down the comment section but  most importantly Please Subscribe also we got some   awesome illustrations and notes that I really  suggest you guys go down in the description box  

below check out our website and you guys  can follow along with me as we go through   this I really think it'll enhance your learning  experience but let's talk about cell membrane   so we go through the cell membrane I want us  to go through the structure and the function  

right so the two components here the structure  of the cell membrane well first what does the   cell membrane do like what's its kind of overall  justificational purpose really the cell membrane   is just supposed to act as a barrier between the  intracellular and the extracellular fluid there's  

a lot of different components of it though so  when you look at the structure you see this   kind of like black thin membrane here that's the  cell membrane and the cell membrane is made up of   very very special components of it so this black  part that will actually zoom in and look at here  

is called the membrane lipids that's the first  part that is actually super super crucial and   there's so many different components here such as  phospholipids such as the actual fatty acids such   as cholesterol so we'll go through all of that  the second component here is going to be these  

orange proteins that are kind of spanning the cell  membrane or linked on the inner or outer surface   these are called membrane proteins and there's  so many different types of these as well and they   have various different functions okay and then  the last component of the actual cell membrane  

is that you see on these actual proteins these  membrane proteins they have like these little like   extensions of lipids and sugar residues which are  represented by the pink and then this baby blue   color this is like glycoprotein glycolipid Network  on the outside of the cell and it's really really  

important we'll talk about later it's called the  glyco calyx so those are the three components   that make up the structure of the cell membrane  let's dive into each one of them and talk about it   the first thing is the membrane lipid so what  I want to do is I want to take a piece of this  

actual cell membrane and we're going to zoom  in on it as you see here and then on this side   here this is the extracellular fluid so this is  the fluid outside of the cell and then here is   the intracellular fluid the fluid inside of the  cell so this is inside the cell outside the cell  

now when you zoom onto this membrane you  see a lot of different cool things right   the first thing is you see these kind of like  blue dots if you will see these blue circles   these are actually called your phospholipids  so there's an outer membrane our outer membrane  

inner membrane and that's made up of the  phospholipids okay so the outer membrane and   inner membrane have been specifically something  really really cool and it's made up of phosphates and sphingocides sphingocides are sphingosines  

now these are really really cool so phosphates and  sphingosines basically what I want you to remember   is that they have a negatively charged surface  to them they're negatively charged so phosphates   have a negative charge to them and sphingosines  have a negative charge to it the specific concept  

that I want you to understand is that these are  actually Associated on the outer membrane and on   the inner membrane now if you really wanted  to look at it like this the outer membrane   is actually made up of very specific types of  phosphate groups one of them we call phospha  

to dial choline another one is the sphingosines  and there's a very specific one here called   sphingo myelin right but these are basically  going to be the phosphates and sphingosines   that make up the outer membrane of the cell  on the inner membrane of the cell it's still  

phosphates we just give them a very specific type  of phosphate component here and these are called   phospha to dial serine and then there is other  ones like ethanolamine but basically the big   thing that I want you guys to understand  here is that on this outer membrane and on  

this inner membrane you have phosphates and  sphingosines which basically have a negative   charge to them which we'll talk about  later gives them a certain degree of   polarity in other words they love to interact  with water because they have a charge to them  

so therefore this phosphate and sphingosine groups  that are on the outer aspect of this phospholipid   bilayer they are hydrophilic so this component  here is hydro Philip which is a beautiful concept   here because it allows for it to interact  with the extracellular flu which is water and  

it's hydrophilic here which allows for it to  interact with the water in the intracellular   fluid so that's a really really cool concept all  right so we know now that the outer membrane and   the inner membrane is made up of phosphates  and single scenes particularly in the outer  

it's phosphodel choline and sphingomyelin  on the inner it's phosphoidal serine and if   you really wanted the extra one here I'll  write it down this one is called phospha   to dial ethanolamine ethanolamine is the other  one but basically it's phosphate groups that have  

negatively charged that make them hydrophilic  that's really the big thing I want you to give   the second component is these like little  red squiggly lines that are coming from the   phosphate head what is that those are fatty  acids so this component here that are coming  

from these phosphate heads is fatty acids so  the second component is going to be your fatty   acid chains now the fatty acid chains are  really important in the sense that they're   made up of two types of fatty acids that are  actually going to be as kind of stuck within  

the center part in between here so in here is the  fatty acids all of these and the big thing I want   you to understand about these puppies here is  that they are hydrophobic they're hydrocarbon   chains they hate water they do not want to  be anywhere near water and that's why they're  

tucked in between they do not come into contact  with the exercise of the fluid Isn't that cool   so the fatty acid chains here there's two  types they're saturated which just means that   it's kind of like these straight components  here a lot of hydrocarbon chains in there or  

it can be unsaturated which may have may have a  double bond in it which gives it this special type   of Kink to the actual structure which is really  really important we'll talk about later when we   get into fluidity but these are the big things  that I really want you to understand the last  

component here of the membrane lipids is going  to be these kind of like pink structures these   pink circles that are kind of extended or kind  of deposited into the cell membrane you see how   they're deposited into the cell membrane this is  cholesterol this is cholesterol and cholesterol  

is very very important for the actual stability  of the cell membrane and we'll talk about later   how cholesterol has a very significant  involvement in what's called fluidity so   the big thing to understand as a quick recap  here is we have again membrane lipids as one  

of the components here what is it made up of  three particular things outer membrane inner   membrane which interact with the water between  the intracellular and extracellular fluid is   having these phosphates the phosphate head of the  phospholipids or if you really want to be a little  

Advanced these things called sphingosines on the  outer sphingomyelin and phosphatidyl choline on   the inner phosphatidylserine phosphatidyl  ethanolamine big thing to understand is   they're negatively charged so they very nicely  interact with water because they're polar  

in the inner in between coming extending from the  phosphate and sphingosine heads in the center is   these hydrocarbon fatty acid change they're  saturated meaning no double bond unsaturated   has a double bond which gives a little Kink to  it we'll talk about why that's important later  

but these hydrophobic they don't like that water  so that's why they do not interact with the fluid   of the intracellular and extracellular fluid  and then lastly cholesterol is deposited into   the cell membrane as well these are the big  components let's now come down and talk about  

the next important component of the cell membrane  and these are the membrane proteins so membrane   proteins are really really cool and they can  actually be completely spanning the entire   cell memory you see how it goes from the outer  membrane all the way to the inner membrane and  

allows for a connection if you will where maybe  certain things can kind of travel in or travel out   these are really really cool these proteins  because they span the entire membrane we call   these integral or specific type a transmembrane  protein so again what is this one here so this  

one here specifically it spans the entire cell  membrane this can be called an integral this is   an integral protein but a very specific type  of it spans the entire membrane which is the   most common type of integral protein this is  called a trans membrane protein and this is  

a great example of like your Ion channels or your  carrier proteins these basically have the ability   to interact with the extracellular fluid and the  intracellular fluid that's a pretty cool concept   they're ones are proteins that basically  are linked kind of like very very weakly  

so in other words they may have like slight  positive charges slight positive charges that   allow for them to be able to interact with the  phosphate groups because phosphates are negative   and sphingosines are negative these are called  peripheral proteins so these are called peripheral

proteins and again I think the big thing to  understand here is that integral proteins   you see how they're completely spanning  the entire membrane these have a strong  

kind of lipid Bond so they have a very intimate  kind of like strong bond between the phospholipid   bilayer very strong whereas this one here  your peripheral proteins these have a weak   type of lipid bond in other words they do not  love to interact with them so it's a very weak  

more like hydrogen bonding so if you really  wanted to remember this one's your hydrogen   bonding where this one may be more of  an unstrong like kind of covalent bond   so these are very very strong bonds and  that's another important concept to take away  

all right so that covers again membrane proteins  these are proteins which either completely or   in kind of invaging into the cell membrane and  they may span the entire membrane transmembrane   this is an integral type or they can have a weak  interaction with the cell membrane electrostatic  

hydrogen bonding and they do not span it these  are peripheral proteins okay next thing is let's   talk about the glycocalyx all right so the next  component here is the glycocala so the glycocalyx   is really interesting so we have the protein  structure here right so here's our proteins that  

are basically again you could have the two types  the integral which if it spans the whole membrane   it's called transmembrane or if it's kind of see  a softly linked to the inner outer surface again   these are the peripheral proteins but sometimes  these proteins can have these kind of like sugar  

residues kind of linked up to them right so  we're going to just call this a sugar residue   really it's just kind of like an oligosaccharide  and so when you have a protein and a sugar kind   of combined we call that a glycoprotein and this  makes like this really really powerful Network  

on the outside of the cell so this is called  your glyco proteins and this is one big thing   the other component which is also kind of crucial  is that sometimes you have some of these kind of   like lipid molecules I'm sorry sugar molecules  which kind of come off of the cell membrane  

and so because the cell membrane is primarily  kind of a lipid complex if you have these sugar   residues again this is another sugar residue kind  of linking off of the cell membrane and the cell   membrane was primarily lipids phospholipids  fatty acids cholesterol then this would be  

called a glycolipid so sometimes we can also have  these glycolipids and really the combination of   these glycolipids and these glycoproteins kind  of form this mesh Network on the outside of the   cell and that's what's called your glycocalyx  so what I want to do now is we've covered all  

the structures we've covered the membrane lipids  with the components of it so the phosphates in the   sphingosines the fatty acids the cholesterol we  cover the membrane proteins the integral or the   peripheral and we cover the glycocalyx which is  the glycoprotein and glycolipid structure on the  

outer surface of the cell now we got to do is go  through each one of those and talk about what are   the functions of the membrane lipids what are  the functions of the membrane proteins what are   the functions of the glycocalyx let's do that  now all right my friend so let's actually start  

talking about the functions of the cell membrane  so first one is the glycocalyx right it's the   easiest one so we'll cover that one first then  we'll go into the membrane lipids they're just   a little bit harder of a function and then we'll  finish off of membrane proteins they get a ton of  

functions so first thing is when we talk about the  cell membrane again we know the three components   right glycocalyx is one of those glycocaly is  made up of the glycoprotein glycolipid network   on the outside of the cell and what that's really  good for is two particular things one is that  

this really helps the cell to be able to hold  on to water so it's really good at being able   to regulate the movement of water kind of in in  and out of the cell it's really really good at   that and so what it's designed to be able to do  is to decrease cell dehydration that's a really  

great thing about this glycocalyx is that it's  really really good at being able to reduce the   dehydration of the cell because it controls  the movement of water in and out of the cell   because of this crazy kind of glyco protein and  glycolipid can't forget about that puppy there  

Network on the outside of the cell all right so  that's one particular thing the second thing which   is actually really really cool is antigenic  function so it has a very important type of   antigenic function you're like what that mean  man so antigenic function is it's really what  

allows for our cells our immune system cells to  recognize something as though if it's host or if   it's foreign it's not supposed to be there it's  abnormal I'll give you two examples one is with   respect to our immune system so our immune system  is a really really great example of one so here's  

a host cell and here's a foreign cell on this  host cell it has a very specific type of network   of glycoproteins and glycolipids that maybe  will make up you don't have to memorize this I   just want you to understand it maybe this whole  kind of structure here on this host cell makes  

up something called a MHC one complex and we'll  talk about this later when we get into Immunology   but this is what basically helps us to recognize  a normal human you know nucleated cell from a   foreign cell so this is a very specific type  of structure a very specific one so the immune  

system cells will come and what they'll do  is they'll read and they'll say okay okay   this cell definitely has I can can detect that  that's a normal mhc1 complex that's a normal   glycocalyx whereas if I go over here and I try to  recognize this one this one is not a glycocalyx  

that I actually recognize it does not have that  very classic MHC one component so this is not a   MHC one component so therefore I'm going to  kill this cell and keep this cell alive and   healthy and so that's one of the cool ways so  it helps with being able to control our immune  

system being able to recognize if something is  foreign versus our own and the same concept we   can think about this with red blood cells so red  blood cells have these specific antigens on them   these specific glycocalyx molecules that gives  them the blood type A gives them the blood type  

B gives them the blood type a b or they have none  of them none of these and so we call that o right   so all of these different types of proteins  basically help us to recognize what type of   blood type the patient has so it's really  really cool right so it's very helpful and  

blood typing and so that's one way is it can help  to recognize our cells our red blood cells of the   person versus another persons who maybe doesn't  have this specific a or the b or the a b maybe   these are very different so maybe this donors is  some type of different red blood cell so let's  

say that in this patient maybe all of these  his blood type these image these uh glycocalyx   proteins all represented type A blood and then you  give them this donor which represents type B blood   this may not be a compatible type of blood typing  and that's an important thing so it would help our  

actual immune system cells to be able to recognize  that this is foreign not our actual blood cell   that we should accept and this one is good  because it can recognize these different types of   antigens on the surface the glycocalyx proteins  and if it notices something that's different  

it'll actually release antibodies to bind to the  donor red blood cell proteins and cause them to   Clump and Destroy whereas it will not release  any types of antibodies to actually combine   with these proteins these glycocalic proteins to  cause it not to agglutinate and therefore not to  

clod so that's a really really cool thing so the  big things that I want you to take away from the   glycocalyx is that it prevents cell dehydration  and it plays a very very important role in acting   an antigenic function recognizing our cells from  foreign cells and that's a really important thing  

with the example of the immune system and blood  typing okay now let's come and talk about the   membrane lipids and all the functions they have  all right so when we talk about the next component   which is the membrane lipid so we know that  glycocalic is important for antigenic function  

preventing cell dehydration the second thing  is the membrane lipids now membrane lipids are   really really cool right and in a very specific  way there's two very important components to the   function of membrane lipids one is called fluidity  so it's the ability of the cell to adapt its shape  

and movement and it's really really cool and I'll  give you a great example of that when we get over   into the next part of the lecture here but with  fluidity there's three important factors that you   guys will be tested on that influences the degree  of the actual cell to adapt its shape and movement  

in other words does it want to be rigid in a very  tight structure not a lot of movement going on or   does it want to be a little bit more relaxed  open and allow for more movement and Mobility   so the three important components that influence  that my friends very very important is temperature  

so temperature has a very profound effect on  fluidity so hot and cold the next one is the   presence of cholesterol so cholesterol believe  it or not I told you it has a very important   component to the stability of the cell membrane  it controls fluidity of the cell membrane and  

the last one is the types of fatty acids and you  guys remember the fatty acids that are basically   in the center of that actual structure to the  actual cell membrane right we said that there's   the fatty acids there's the hydrocarbon chains  which are the hydrophobic portion now these are  

the three things that affect fluidity the ability  of the cell to adapt its shape and movement   now let's think about this and what I really want  to do is I want to talk about what Will basically   with these particular factors increase or  decrease fluidity so if we increase fluidity what  

do you notice there's a lot of space between the  phospholipids in all of these structures there's   a lot of space do you notice that between each  one of these if there's a lot of space there's a   lot of degree of movement here as well so there's  an increased fluidity increase space between the  

phospholipids and increase kind of movement now  with temperature I just want you to make it too   very very simple if it's really really hot really  really hot you're going to want to be sitting   close to somebody no no because they're radiating  it on you you're radiating heat on them that's a  

similar kind of concept that's why I want you to  remember it so a very very high temperatures the   fluidity will increase because I want you to think  about the phospholip is just kind of separating   from one another this is very very crucial when it  actually comes to the presence without cholesterol  

the other concept is if we decrease fluidity so if  it's high temperatures whenever it's really really   cold what do you want to do you want to snuggle up  to somebody you want to get close to your friend   your family member your dog whatever it may be  to kind of get really really warm right so you  

guys can radiate heat on each other so you guys  get close to one another and so really really low   temperatures especially in the presence without  cholesterol I need to write this down especially   without cholesterol then these dang phospholipids  will get tight with one another and the cell  

membrane will get rigid and very very tight and  again not allow for a lot of movement and mobility   of the phospholipids same concept for cholesterol  cholesterol I want you to think about when   cholesterol is present and high amounts it really  causes the phospholipids to come and stick Imagine  

It Like Glue so if there's lots of cholesterol  it'll stick it'll act like a glue to stick the   phospholipids close to one another if there's very  little cholesterol the phospholipids won't have   the glue to stick with one on there and they'll  drift apart so in this situation this would be  

very little cholesterol very little cholesterol  and then in this particular so again here's the   one specific example when cholesterol is low you  would think oh that increased fluidity but Zach   you said over here that low temperatures without  cholesterol this is the only other exception that  

when cholesterol is low if it's at Cold temps  it'll compact the actual phospholipids down   but if we go over here lots and lots and lots of  cholesterol guess what phospholipids are going to   stick to one another really nicely now and so  that's going to be again this concept here for  

a decrease decrease in fluidity now last one here  is types of fatty acids this one's actually really   cool so remember I told you that there's two types  of fatty acids one is it's saturated and saturated   kind of gives you this straight beautiful line  like this one and then unsaturated has a double  

bond and the double bond gives a little Kink to  the structure now imagine if I'm trying to sit   next to somebody and I'm like this legs wide  open arms wide open can the phospholipids be   close to one another no and so they separate out  very far over one another whereas if I'm like a  

saturated I'm kind of sitting on the plane like  this we're hating my life right really really   close arms close together legs close together  I can fit a lot of things on the side of me so   that's the same kind of concept here that if  we want to increase fluidity put some Kinks  

into the mix that's a little weird but you want  to basically increase the amount of unsaturated   fatty acids and that'll basically increase  the spacing and increase the fluidity   if I want to make it to where it's really tight  kind of impact structure then I'll basically  

increase the amount of my saturated fatty acids  no double bond No Kink and therefore these can   kind of tightly compact one another and this is  the concept that I want you to understand about   fluidity this is very commonly tested all right  now that we understand one of the big functions  

of the membrane lipids let's talk about one more  which is again going into the transport concept   all right so the next thing with membrane lipids  not only is their fluidity is a very important   concept A Very commonly tested guys please  don't forget that please the next thing is  

there's a concept of Transport so the movement of  things and this could be things that are actually   moving across the cell membrane or it could be  things that are moving within the cell membrane   you didn't think it should hear that right but  it's pretty cool so one of the concepts that I  

want to talk about is this concept of like like  simple diffusion across the membrane so across   the membrane and this is really really cool so  when you think about it the cell membrane is a   phospholipid bilayer phosphates on one side  phosphates on the other side and then the  

fatty acids in the core of it right that's what  we know phosphates and sphingosines are on the   inner and outer because they're negatively charged  hydrophilic and then fatty acids hydrophobic in   the inner side now what's really really important  is that certain substances have the capability of  

moving across this cell membrane in and out but  the way that these things move across is because   the lipid bilayer has on this inner surface  these fatty acids it's very very hydrophobic   right so again the hydrophilic component is yes  this thing on the outside but this is the problem  

here it's this is the problem this component  the hydrophobic component so whenever things   have to move through they have to be able to  dissolve within this hydrophobic component and so   examples of things that are able to move across  here is things like oxygen and CO2 that's one  

another one is things that are like a small  small structures so very very tiny structures   other things that are really really important  here are things that are lipid soluble   and so lipid soluble structures so steroid  hormones is a really really big one as well  

so it really has to be small nonpolar  or lipid soluble to be able to Simply   diffuse without any kind of ATP involvement  but to dissolve across the cell membrane I   like to remember that leg dissolves  like so if it's small nonpolar and  

lipid-soluble it's just like the cell  membrane it'll easily dissolve and move   across the cell membrane so I want you to  use that terminology that like dissolves like that because this cell membrane especially  the inner component is hydrophobic it's nonpolar  

we need things that are very very tiny that can  fit between the hydrophobic Tails or between the   phosphoid phosphate groups or we need something  that's nonpolar like the hydrophobic Tails or   hydrophobic in other words lipid soluble that  can diffuse easily across the cell membrane  

that's one concept the other one is diffusion  within the membrane diffusion within the membrane   and I just think that this is super super  cool I don't want you guys to get too crazy   I just find it so fascinating that when you  think about the cell membrane right we know  

that we have these phosphate groups and we  know that we have the phosphate groups on   the inside and the outside and then we have the  hydrophobic Tails do you know that they can move   I could literally move this phosphate group here  to here and I could move this phosphate group  

from here to here and it's constantly happening  they're constantly moving the fossil lipids are   constantly moving from side to side within the  membrane you know what they call this they call   this lateral diffusion so they literally call this  lateral diffusion and what's really cool is if you  

were to tag let's say that you just tagged one of  these philosophy groups and you were to follow you   would see it just moving all around the cell  membrane it's so cool the other concept here   is that if I have a phosphate group here I could  move it to the inner membrane so I can move it  

from the outer membrane to the inner membrane or  if I wanted to move this from the inner membrane   to the outer membrane I could do that as well  so you can flip flop back and forth between the   actual inner and outer membrane so if you were  to tag one of these philosophy groups you'll be  

able to see it at some point maybe on the inner  membrane maybe later you'd see it in the outer   membrane maybe later you'd see it on the inner  membrane that's called transverse diffusion   trans verse diffusion and we need specific  enzymes really that help us to perform that  

type of task and I just remember by where they're  going so if it's going from inner to Outer then   it's a flaw Pace I'm not even kidding I'm not  making this up it's literally called a flop   haste and then if it's going from the outer to  the inner then this one is called a flip paste  

I wish I was making this up but these are  enzymes that are basically helping to move   these phospholipids from one end to the other from  the outer to Inner inner to Outer it's really cool   but that covers the basic concept of the membrane  lipids so fluidity is one really really important  

component knowing the three things that influences  that temperature cholesterol types of fatty acids   knowing that the transport across the cell  membrane is important so simple diffusion   of small nonpolar lipid soluble molecules that  easily dissolves across the cell membrane and  

then lastly knowing that the phospholipids can  actually easily travel along the cell membrane   in a lateral pattern or they can flip-flop back  and forth between the outer and the inner membrane   and then now what we're going to do is talk about  the membrane proteins in their function all right  

my friend so now we're going to talk about the  membrane functions particularly pertaining to   the membrane proteins so this is the integral  proteins which is specifically the transmembrane   protein and the peripheral proteins what can they  do there's a lot of things that these things can  

do so we told you that the membrane lipids only  allow for what type of diffusion simple diffusion   of small nonpolar lipid soluble molecules well  there's lots of other molecules that are large   polar and water solid valuable what about those  how do they get across the cell membrane we need  

transport proteins to be incorporated into the  cell membrane transmembrane proteins to act as   channels or carriers to move those large polar and  water-soluble molecules across the cell so we may   need again this type of channel protein so this  is a channel protein this may be a carrier protein  

and what they may do is is they allow  for what type of transport very large   large polar and what else water soluble transport  of things across the cell so that's really really   important so it'll allow for things like charged  molecules to move across the cell allow for things  

like proteins to be able to move across the cell  so that's really really really important now   another really cool concept here is that proteins  are not only involved kind of in being embedded   into cell membrane they can be transient in  other words they can kind of move and attach  

so remember these peripheral proteins maybe  there's peripheral proteins that are on the   inner cell membrane you know here maybe molecules  that I want to either move to the cell membrane to   release and we call this exocytosis so exocytosis  or maybe there's molecules that I want to bring in  

to the actual cell so this is called endocytosis  this is another example of where proteins can kind   of cooperate this process and you know what's  really also cool look how the phospholipids   of this vesicle fuses with the lipids of this  cell membrane look at how the phospholipids of  

this cell membrane forms this phospholipids of  that vesicle that's an example of fluidity so I   love this example of exocytosis and endocytosis  because this is one of the perfect examples of   these two exhibiting a concept of fluidity I  just think it's so darn cool how that happens  

but that's one of the functions of membrane  proteins is they allow for transport of very large   water-soluble polar molecules across the cell  membrane that wouldn't easily dissolve across the   lipid-soluble hydrophobic fatty acid tails of the  actual cell membrane remember light dissolves like  

what's another function well let's say here  I have a vesicle in this vesicle in order for   me to be able to stimulate it to fuse with the  cell membrane release these particular molecules   I have to have a hormone let's say this is a  hormone it has to bind onto a particular type  

of receptor and when it activates or stimulates  this receptor it sends signals that then will   fuse actually activating this vesicle to fuse  with the cell membrane so it may activate some   type of second messenger system which is actually  pretty cool so there's another function it allows  

for me to be able to take an extracellular  so this is the extracellular fluid here's the   intracellular fluid it allows for something in the  extracellular fluid to stimulate a protein trigger   a signal in the cell in the produce a response  that's another important concept of proteins  

another cool function is they can link a  cell one in cell 2 together so there may be   these integral proteins that are on the outer  surface of the cell that link to the integral   proteins of another cell and that's a really cool  concept we'll talk about these a little bit later  

um when we get to cell Junctions but  this could be things like tight junctions   right we'll talk about these this could be things  like your desmosomes right we'll talk about these   this could be things like adherence Junctions and  we'll talk about these so this is a really cool  

concept of where you have these structures that  allow for cells to link up with one another if by   some chance you understand pathology where maybe  I destroy these cell adhesions and the cells can't   stick with one another and they start separating  that's an important concept okay what else  

we come down here we know that the next functions  that are also really really key here is going to   be enzymatic function believe it or not let's say  that there's actually some type of enzyme out here   let's say or some type of substrate so we usually  we represent substrates as a plus b right maybe  

there's an enzyme here on the outer surface of the  cell and in order for this to be able to become   activated and turn into C let's just say c plus d  c plus d this is the reaction they use this as a   common reaction this enzyme this is our enzyme  he's the one that catalyzes or stimulates the  

acceleration in this particular step so he will  allow for the increased speed of reaction same   concept maybe it's inside of the cell maybe it  doesn't have to just be outside the cell a plus b   will have to interact with this enzyme and make C  plus d he will stimulate this is an enzyme this is  

an enzyme and they may stimulate the intracellular  and extracellular synthesis of particular types of   substrates that's a really cool concept so so far  we've got transport we also have what other thing   transport we have cell to cell communication  we have a receptor we also allow for enzymatic  

function another one is cell communication so  again cell one sell to maybe I want this cell   to become activated so I want ions positive ions  to flow from this cell into this cell and we call   these and they're very common in muscle cells  Gap Junctions so this is another example of  

something that we'll talk about later when we  talk about cell Junctions called Gap Junctions   very cool concept the last but not least thing  that's actually really important here is going   to be the cell attachment to The extracellular  Matrix so you know whenever we have cells like  

epithelial cells epithelial cells they love to  connect with the outside surface sometimes to   give stability to the cell membrane so sometimes  we have like little connective tissue structures   that are nearby here's some connective tissue okay  so here is going to be the connective tissue that  

we're zooming in on so here's this we're zooming  in on this connective tissue that these cells are   linked with in order for us cell to kind of be  really strengthened to the outside surfaces in   this case the connective tissue lining or the  basal lamina we need the proteins of the cell  

membrane to link with the connective tissue of the  extracellular Matrix and this is that connection   right here these linkage between the two and this  is important because there's a lot of different   things that do this a lot of different structures  right but this is a really really important thing  

that I need you guys to understand one great  example is like hemidezmosomes they actually   allow for that kind of process here so we can  call one of these as an example is Hemi desmosomes in this video we will be discussing the structure  of the cell membrane when scientists looked at the  

selectively permeable cell membrane they  described its structure as a fluid mosaic you might know that a mosaic is  a picture made up of little tiles like a mosaic the cell membrane is  made up of different parts as well

the cell membrane has two layers of phospholipids  referred to as a lipid bilayer the lipid bilayer   isn't rigid the phospholipids in it have the  ability to move in a flexible wave-like motion let's take a closer look at a few phospholipids  the round head portions are hydrophilic which  

means they are attracted to water both the  extracellular fluid meaning fluid outside the cell   and the cytoplasm inside the cell are  mostly made up of water so the hydrophilic   phospholipid heads of the outer layer will  be oriented toward the extracellular fluid  

and the heads of the inner layer  will be oriented toward the cytoplasm   the phospholipid tails are hydrophobic  which means watery areas repel them   so they Orient toward each other in a direction  as far away from the watery content as possible  

there are also scattered proteins  embedded in the phospholipid layers   some with carbohydrates attached so in the fluid mosaic model the cell  membrane is made up of different parts  

and these parts make up a flexible boundary around  the cell but how do the majority of substances get   in or out of the cell some molecules seep through  the little spaces in between the phospholipids   which make up the majority of  these semi-permeable cell membrane  

however other molecules are too big to  fit through the cell membrane this way   so how do these larger molecules  pass through the cell membrane   the molecules move through proteins  embedded in the cell membrane  

either from the extracellular area into the cell  or from the intracellular area out of the cell   these substances will move through  tunnels made up of these proteins   we'll explore how things move through the  cell membrane in Greater detail separately

[Music] so that really covers all the functions of  the membrane proteins the membrane lipids   the glycocalyx and all the components of  the cell membrane I hope it made sense I  

hope that you guys enjoyed it and  as always until next time [Music]