today we're going to talk about section 7.2 section 7.2 deals with the plasma membrane all right we looked at this cell over here and we said the plasma membrane was what surrounds the cell and we're going to look at it in some more detail than we've looked at it before are you guys ready yeah all right let's go uh inside this section first we're going to talk about maintaining a balance okay that's very important when we're talking about the plasma membrane then we're going to talk about about the what the plasma membrane is we're going to talk about the structure of the plasma membrane and that is the content that we're going to deal with today we're going to talk about maintaining a balance first uh plasma membrane is a boundary between the cell and its environment if we didn't have a plasma membrane there would be no overall structure and the stuff that's inside would not be separated from the stuff that's outside and we don't like that we don't want that why do we have a plasma membrane one of the main reasons is you want to let the good stuff in and you want to keep the bad stuff out and send the bad stuff out so good stuff would be things like nutrients bad stuff would be things like waste you want the good in and you want the bad out the plasma membrane the plasma membrane maintains homeostasis anybody remember what homeostasis is anybody remember what homeostasis was we spoke about it once in the past a consistent environment right you want things to be basically you want it to be in Balance you want the right things inside you want the wrong things to be outside and that's the way it is you can compare the plasma membrane to the walls of your house you have a house well hopefully you have a house or an apartment or something of that well you don't have one your parents have one and you live in a house you have one man you you're set if you have a house already sweet I wish I had a house when I was your age anyhow so plasma membrane keeps the good things out in the bad things out you have your house you have walls hopefully there's certain people you don't want to come inside your house right like Mr Samuel right I know I understand all right certain people you don't want in certain people you do want in how do you regulate that lo you close the door you lock the door you say you know what I don't want you in my house I'mma close my door you see Mr Samuel coming up to the door you're like oh no it's Mr Samu you shut the door right hide turn off yours hide and turn off all your lights you sound like you've done this before no you would never do that right all right regardless of how you choose to do it you have your walls in your house you have the doors you have the windows and you can regulate what comes in you can regulate what goes out if Mr Samuel comes in your house and he's giving you a headache you just kick him out right good good answer I like that oh okay okay got you all right so that that is kind of what the plasma membrane does for us it helps us to regulate what comes in and what does not come in all right so the first thing is it maintains homeostasis next is what we call selective permeability in other words it allows some molecules into the cell and keeps some out what does permeable mean if something is permeable what does that mean some stuff can go through it right what does Selective mean only certain things okay only certain things you're picky and choosy as to what you let into the cell do you want any and anything to get into the cell no obviously not so the membrane is selectively permeable in that way some molecules can cross across can cross across cross across some molecules can cross the plasma membrane for example water can get into the cell easily it can get out of the cell easily and then others that are bigger than water for example or not specific to not not able to just pass across the membrane they can go through channels and that's like your doors right that's your doors you you want people to come in but unfortunately or fortunately depending on how you look at it people can't just walk through your walls I mean that would be kind of cool if you could walk through walls but try all right uh let's talk about the structure of the plasma membrane the plasma membrane is composed of what we call a phospholipid by layer what is a lipid again fat fats and oils and we spoke about the structure of um the lipids and we spoke about that lipids are normally one molecule of glycerol attached to three three what do you guys remember fatty acids correct but the phospho lipid is a little different is in that it's a lipid with a phosphate group attached so instead of Three fatty acids you have two fatty acids and you can see that here and here we have a phosphate group that's attached so it only has two fatty acid tails and it forms kind of like a sandwich so you have one layer at the top one layer at the bottom and the phosphate groups forms these polar heads what does polar mean again okay water was Polar Polar and it had some of those features um now does it mix with water or not no polar yes yes or no yes yes polar mixes with water non-polar mixes with does not mix with water good job it mixes with nonwater all right so is oil polar or non-polar non non-polar is salt polar or non-polar salt salt yeah really so what is it okay so salt is polar right next question the soap mixed with oil and dirt and that type of stuff yeah so you guys asked the question which one of you are right both of you are soap soap is kind of like like a not a Foss liid but it's kind of like it in that it has a polar part and it has a non-polar part which is good right because you want it to mix with water and you also want it to mix with dirt and oil and all that stuff right so that when you take a shower you get rid of all the dirt and the oil and all that stuff does that make sense isn't like soap does soap it has oil in it well it depends on the type of soap I don't know about that but yes that that is true some of it some of it does is made out of that some of it is made out of different things and all right so we have a phosphate group forming a polar head which is what we see here and then we have the fatty acids and tail the fatty acid Tails forming the non-polar tails in the center which is good right because is there water inside the cell no yeah yes is there water outside the cell yes there's water all around the cell water in the cell so you want the polar heads to be on the outer ends so that it can be exposed to the water on both sides let's talk a little more about the structure of the membrane and what we're going to talk about is called the fluid mosaic model what does fluid mean liquid right it flows what does mosaic mean what kind of a picture it's like a b those pictures where you have like a bunch of smaller pieces that come together right um to form something to form a large picture yeah like a puzzle said not not really like a puzzle but kind of but it's it's not in any specific way you could put one piece with another but you take individual things put them together and you form a bigger thingy except for if you're thinking about a a mosaic picture it's usually a bunch of smaller pictures pictures to make oh yeah and and that's and that you you guys know what I'm talking about right so that's the type of that's the concept we're dealing with when we're dealing with Mosaic you have a bunch of little particles that come together to form a bigger overall picture so let's talk about the fluid mosaic model and why we use this model to describe the the plasma membrane the membrane is fluid why is it fluid because we have phospholipids and they kind of move around in the membrane like a like the water in a lake it does not stay each phospholipid does not stay in one particular position it actually flows around the cell throughout the plasma membrane so it's very fluid where that's concerned on the other hand it's also considered to be Mosaic because we have a bunch of proteins in the membrane that also move so you have a bunch of individual proteins and proteins that come together and so on that are all throughout the plasma membrane so we have the phospholipids and we have the proteins and this is why we call it the fluid mosaic model so what other things do we find in the plasma membrane there are a few other things that we're going to talk about number one we have cholesterol cholesterol is found in the plasma membrane do we need cholesterol yes we do but if we have too much we can have some problems right um cholesterol this is what cholesterol does when it comes to the plasma membrane it helps to stabilize the plasma membrane and prevents the phospholipids from sticking together so they are all throughout the plasma membrane and it helps to make keep it stable and keep the phospholipids from sticking together now what happens if you have too much cholesterol okay it could block your arteries um and one of the reasons why is because cholesterol helps to stabilize the membrane if you have too much what's going to happen to the membranes too hard okay stuff is going to get too hard too rigid and then that can lead lead to some problems cheer you eat Cheerios according to the commercial right let's now talk about transport proteins those are proteins that span the entire membrane and form channels for specific molecules to enter and leave so that's like the door we have these channels that go through that if certain molecules want to come in like if sodium wants to come in um pottassium chloride and a number of other things they want to come in they have to go through these transport proteins and then let's talk about some other proteins and carbohydrates that are on the external surface and we're going to look at a picture of this in the next slide but we have these proteins and carbohydrates that are on the external surface that helps with identification it helps the body know what type of cells are in a specific location all right the immune response for example has to do with this so that it can identify the cells that it needs to identify and do what it needs to do and we're going to talk a little more about that in a later chapter and then we have proteins on the inside surface on the internal surface that provide flexibility by attaching the plasma membrane into the cell's internal structure so these are some other components that we have in the plasma membrane and here we can see looking at the plasma membrane uh here's extracellular fluid what does that mean extracellular extra extra what does that mean not NE because this this is extracellular and this is intracellular so what would okay so extracellular means outside of the cell this is the plasma membrane and inside here we have the cytoplasm here we have a transport protein and stuff can go through it we have some proteins and carbohydrates on the outside surface and what does that help with again anybody remember in the previous Slide the the the carbohydrates and proteins on the outside what does that help with transport no that was the transport proteins no that's what does that what what what stops the phospholipids from sticking together CH cholesterol okay and here we have the cholesterol here and the other proteins and carbohydrates on the outside what did those do again no it's in your hand out the other proteins and carbohydrates on the external surface nope what was it sandwich thing it's right there in your hand out helps with identification so remember that the other proteins and carbohydrates on the external surface help with identification then we have proteins on identification so that you can know what type of cell it is so that your body can know what type of cell um certain other cells are coming in contact with and that's also a way that your body can determine when there's a foreign sub substance inside your body because when it goes and it sees these foreign IDs then it knows that it needs to do something it needs to attack those cells so in review inside review in review uh We've looked at maintaining a balance we looked at the plasma membrane the structure of the plasma membrane was the last thing we spoke about we spoke about the fluid mosaic model within that that is the end of this section