alright hello biofans welcome to video lecture number 8 this one's called cell transport as always please make sure you have your skeleton notes out and we will get started okay so cell membrane The cell membrane, now this is the outside of the cell, this is the inside or the cytoplasm of the cell. It's important to know how to label the cell membrane. So one of these guys right here, so it looks something like that. That's called a phospholipid. I'm going to pop up some of these names for you.
That's a phospholipid, and each part of the cell membrane or each layer of it, it's called a bilayer, which means two layers, a bilayer. Okay? you have all these phospholipids that make up this bilayer or cell membrane or plasma membrane as it's called and notice how their head is sticking towards where the liquid would be or the fluid would be and their tails are sticking inside so what does that tell us their heads are hydrophilic and their tails are hydrophobic hydrophilic meaning water loving hydrophobic meaning water fearing doesn't like like water.
Okay, a few other things, there are lots of protein channels in cell membranes. Okay, all of these are proteins. Notice all these purple guys are all proteins.
And then some of these proteins have carbohydrate chains hanging off of them. These are known as glycoproteins. So it'll be glyco and proteins.
All right, here's another picture of a cell membrane. Just a few more things to know. Here's the cytoplasm. Here's your extracellular fluid.
fluid so this is the inside of the cell this is the outside of the cell and just like we were talking about before let's see there are proteins in there they're blue here now all right there's a glycoprotein we just talked about that one a protein channel right here so things can go in or out that way phospholipid hydrophobic tails very important to know hydrophilic heads carbohydrates So just some of the things that you need to know. Okay, so cell membrane, as we just talked about, is composed of a lipid bilayer. Remember, that means two layers. And it's selectively permeable, which means that some things can get out, some things can't, or some things can get in, some things can't.
The membrane proteins have lots of functions, and we saw some of those proteins previously. So they can serve as protein channels, transporters, pumps. Glycoproteins.
Remember, these are proteins. that have carbohydrate chains hanging off of them and they're actually used as identification markers so it's kind of like me busting out my id and being like here you go this is who i am that's kind of what glycoproteins do for a cell and then cholesterol cholesterol is basically used to stabilize the cell membrane so it's actually not a bad thing it's when we start to have so much of it that it becomes a bad thing and it becomes a bad thing because it makes the cell membrane more rigid and less fluid and that's not what you want want. Cholesterol is only present in animal cells, so eating animal products is basically one way to add to your cholesterol, generally speaking.
Okay, so here's an overview of cell transport. We have passive transport and we have active transport, so we can sort of break them up into those two categories. In passive, we have simple diffusion, facilitated diffusion, and osmosis, whereas in active we have active transport. And then at the very end of this lecture, I'll teach you about endocytosis and exocytosis. So that's our general overview.
Let's talk about diffusion. Okay, a few important things you need to know. Number one, solution, a mixture of substances in which the molecules are evenly distributed.
And then we need to know what a solute and solvent are. So a solute is what's being dissolved, a solvent is what's doing the dissolving. So for example, if I have a cup of water, and I want to mix some sugar into to that water.
What would the sugar be? What would the water be? The water would be the solvent, the sugar would be the solute.
So in this picture the red is the solute, right here. The blue is the solvent, and in this last picture that's where we have a solution because notice how they're evenly distributed. okay more about diffusion so diffusion can only happen when there is a gradient which is a difference in concentration so if you look at this slide right here it goes from sort of darkish blue up here and it gets lighter and lighter and lighter as we go down the slide so this is a gradient of blue so when i talk about gradient that's what i'm talking about and dynamic equilibrium is when there is continuous movement but there's no net or overall change when you hear the word net it really means overall alright so equilibrium dynamic equilibrium it's still flowing still moving from one side to another but there's no overall change okay So simple diffusion.
I won't go over this in detail. I'll let you read a lot of it. It's basically when substances diffuse across the lipid bilayer from a high concentration.
Remember, this is very important to a low concentration. So it's going from an area where there's a lot of them to an area where there isn't as much of them. Here are some things that can diffuse across this lipid bilayer that we talked about.
I'll let you read this on your own. And here are things that cannot diffuse across this lipid bilayer. And there's our list of things that can't go through.
Now the rate of diffusion depends on a few things. Let's go through them briefly. So the change in concentration is one of them.
Temperature, that makes a big difference. So for example, if you are trying to mix sugar and water, it doesn't matter if that water is heated up, if it's cold or hot. Surface area, the size and mass of the molecule, just like the last slide. And the distance that it has to travel, the distance of diffusion.
Let's talk about facilitated diffusion. So what's happening here? High concentration, I want to make sure we make a note of that, and low concentration. Notice where the arrows are going.
It's going from up here to down here. So it's going from high to low. What's high to low?
Is that passive or is that active? What do you think? Based on what you just learned, what is it?
And this right here is protein channel. This is sort of acting as the helper. That's why it's called facilitated diffusion. You actually need a protein channel to carry something or to help carry something across from an area of high concentration to an area of low concentration.
Okay, so with facilitated diffusion protein channels like we just talked about they actually provide a water-filled passageway for these charged ions To go through again remember from an area of high concentration to an area of low concentration Some of these channels are always open, some of them have a gate on them and they open and close. These protein transporters and carriers actually bind to large and polar molecules like glucose and amino acids and then they can change their shape releasing that molecule into the cell. It's important to know that protein channels and transporters are specific to the type of molecule.
Something really important to note is that in facilitated diffusion, it's actually controllable. So in simple diffusion, things just happen to go from an area of high concentration to low concentration. In facilitated diffusion, we can actually regulate the number and the activity of the channels of transporters.
So if you go back to sort of this gated action right here. So it's possible to control them and not allow them to go through the membrane. And then it's important to know it's a passive process. They're going from high to low, and that's one of the things that we talked about.
Now here's a CFU, a check for understanding. This is in your skeleton notes. I want you to describe three ways in which facilitated diffusion is similar to simple diffusion and three ways in which facilitated diffusion is different from simple diffusion.
So take a moment and pause the video and answer this question and then come back. Alright, welcome back. Let's continue.
Osmosis, the passive movement of water across a membrane. Now here's something I want to specify. The actual movement of water through a cell membrane is a result of two processes.
One of them is diffusion, one of them is something called bulk flow, which is movement through these things called aquaporins, which is a type of facilitated diffusion. I want to show you what that looks like. So they're protein channels called aquaporins, specifically for water. okay so let's see let's say here's the outside of the cell and here's inside of the cell so water is going to go through these aquaporins and that's that okay so osmosis diffusion of water molecules through a selectively permeable membrane again from an area of high concentration to an area of low concentration okay so remember so far that's what we would we have been covering it goes from high to low I'm gonna come back and explain hypotonic and hypertonic so hold off on that you can come back and revisit this but I want to explain how to something is hyper hypo or isotonic okay so work with me here imagine if we have a beaker of water and this beaker of water is made up of say 95 percent water Okay, it could be 5% whatever else. Let's just say 95% water.
You drop a cell in there, and that cell is made up of, say, 4% whatever, 4% salt. It's not really the salt. you want to concentrate on is what's the rest of it. So if it's 4% salt, it's going to be 96% water.
Okay. So now we have 96% water inside the cell. We have 95% water outside the cell. Where do you think water is going to gonna want to go from an area of high concentration to an area of low concentration okay so where's it gonna go water is gonna go outside there's more water inside than there is outside of the cell so water is gonna go outside when that happens we call this a high per tonic solution right there hypertonic solution okay so the cell basically shrivels wrinkles up like a raisin pretty much okay So let's go back to our example. Again, 95% water in the beaker.
And now let's say we have 6% salt. So 94% water in this cell. Now we have more water outside the cell than we do inside the cell. Where do you think water is going to want to go? It's going to want to go to the inside of the cell.
So the cell is going to sort of blow up. sort of like a hippo which is why we call it hypotonic so I call it hypotonic okay so the cell is basically going to swell up because of what's going on here now in a situation where you have an isotonic solution you have the same amount of water inside and outside the cell so I won't do that example for you but I think based on what we've done you'll be able to tell what isotonic is all right let's move on so plant cells they don't burst when you put them in hypotonic solution so going back here remember we were talking about this and I was talking about how they sort of become like a hippo sort of almost like blow up with plant cells that doesn't happen because of the rigid cell walls which is made up of cellulose remember that and how do we know the cellulose is a sugar it's got that OSE ending. So the force of the water pushing on the cell walls we call that osmotic pressure.
It's an important word to know. And lastly animal cells have to be kept in an isotonic solution with their extracellular fluids. This is a form of homeostasis.
So when we talk in class about homeostasis this is another example that you can bring up. Okay here's another check for understanding, another CFU. What would happen to a cell cell?
placed in a hypotonic solution. How would this be different if the cell had no aquaporins? And in class, we can work with specific numbers. OK, let's move on to active transport.
Protein pumps, this is where they come in when we talk about active transport. So it's going to be a little different here because we've been talking about molecules going from an area of high concentration to low concentration. And now we're going to reverse it. We're going to go from low concentration to high concentration.
So notice here, we're going to go from low to high concentration. How is that happening? It's not natural. Well, it's happening because of the help of this protein pump right there.
Okay, so the molecule... molecule is really being carried by the protein pump to the other side what does that require requires energy which is why it's called active transport all right here's a joke for you hopefully you find it funny if not i'm going to blame mr jones because it's his joke okay active transport energy is used to transport substances against a concentration gradient what does that mean that means it's going from low to high. Remember before we were going from high to low in passive transport.
In active we're going to go from low to high. It requires energy, requires protein pumps. Protein pumps mainly move these ions that you can see right here.
Why are they called ions? Because they have charges. That's why they're called ions. And then thousands of these pumps in each cell are constantly working to basically maintain concentrations of all of these ions that are necessary for osmotic balance.
again homeostasis another example of homeostasis and another CFU why would a cell use active transport see if you can answer that one we can discuss that in class but make sure you provide an answer for it okay we're close to the end endocytosis what does that mean so when i think of endo i think of the word enter okay so this is a situation in which something is entering the cell so let's look at this top picture right there here's a cytoplasm which means the inside of the cell here's the outside of the cell extracellular fluid so if you have stuff that needs to come to the inside of the cell Notice what's happening, the cell membrane is sort of wrapping around this, let's just call it food for now. It's wrapping around it, notice what's happening here. It's actually gonna wrap around it some more, and then it actually goes bloop, and it forms a vesicle.
now it's inside the cell so the whole thing basically entered the cell it's called endocytosis for entering the cell okay so like we talked about vesicles or small bubbles they form the membrane sort of forms around it and brings it inside in endocytosis cells can absorb large molecules or groups of molecules or whole cells even dead cells sometimes exocytosis is the opposite so when I think of so I think you're gonna be able to see where I'm going with this XO reminds me of exit so something needs to exit the cell it's the same idea though so let's go back to this real quick it's almost like this in reverse right starting from here and then moving that way so something needs to exit the cell so it goes this way that way and then eventually that vesicle just opens up becomes part of the cell membrane and all this stuff can leave the cell all right Okay, is your brain full? I know mine is. Hopefully you enjoyed this one. See you in class, everybody.