remind yourselves we're talking about channels now and remember that channels are an example of facilitated diffusion so a channel is basically a tunnel in the cell membrane I drew one here this is an example of a channel and now I'm going to talk about two molecules that are super important to us that have channels in the cell membrane and that's potassium and sodium and if you think about it like let's go ahead and just draw oh look I already started drawing you the potassium channel um think about potassium potassium is um oh gosh let's just make sure I have enough room here potassium is an atom that quickly loses an electron so it's pretty easy to steal potassium is electron which is how it ends up with a positive charge but it's kind of big for a life oriented ion and super important so I'm gonna draw a picture of it what just happened seriously that's not cool that cannot be what my potassium looks like okay so potassium is relatively large because of its positive charge it also ends up having water molecules attached to it like water molecules kind of I don't know hug it stick to it stick to it is better because water molecules are polar and you know that already compare that to sodium we also have sodium channels I'm gonna draw my sodium channel over here and my sodium channel I'm gonna draw it this way on purpose I'm gonna draw my sodium channel significantly narrower and I'm gonna let you think about why that is go ahead is sodium or potassium a bigger molecule potassium is bigger potassium has a molar mass of like 39 and sodium has a molar mass of I think 22 so that I mean sodium I don't know what I just said but sodium has a molar mass of 22 sodium is smaller than potassium okay right now if you look at this are you like dude I know why potassium can't get through a sodium channel do you know why look at it Tao seems huge is potassium gonna be able to fit through the sodium channel not a chance so that alone is gonna make it like a deal breaker for potassium and there's no way that potassium is going to get through the sodium channel sodium is also attached to water molecules and and now watch what happens here in fact I need to make my water molecules more realistically sized okay something something like that all right you might look at this and be like okay sodium is smaller than potassium so why can't sodium go through the potassium channel they're both positively charged like why if sodium if potassium can go through why can't sodium watch this potassium channels have these like brushes on them and it's like a little entry gate and watch what happens the entry gate those little things on the potassium channel touch the water molecules on the potassium and like scrape the water molecules off the potassium once the water molecules are scraped off the potassium guess what potassium can do can totally go through the channel like no problem whatsoever because the water got scraped off take a look at if I were to draw in this view if I were to draw this sodium atom with its water molecules attached still I mean same thing it's an ion it's positively charged but check out I can't brush off the water molecules off of the sodium ion which means by the time this guy gets to the potassium channel it's like too big to go through uh uh nice try doggie you did not get your water molecules brushed off of you you can't come through this opening seriously are you ready for the potassium channel cuz how look at the sodium ion with its water molecules how in the world is it going to get through are you worried we should be worried because if you can't scrape off the water off of your sodium you're not getting the sodium through gives what it does a sodium channel is covered with negative charges inside that are like we love you sodium please come into this awesome negative charged tunnel and we'll have a tea party on the other side and the sodium ion is like I'm feeling the pole I can't it's like the tractor beam what is that from Star Wars the tractor beam is pulling the sodium in and sure enough that negative charge is so strong that the negative pulls that sodium and the sodium water molecules just get fluffed off in the sodium gets water slept off and passes right on through potassium is like I want to go through the tractor beam too but can the potassium molecule even fit look at that thing it's huge I'm sorry potassium you're gonna have to drop some pounds before you can go through this tractor beam that's like good luck because if potassium drops some pounds then it's not potassium anymore right and then it's gonna be sodium and then it can totally go through how unbelievable is that channels can be dated so both of these channels can actually have doors on them and you can imagine that if I had a big old gate on my channel I don't care how big the tractor beam of negative charged pull is I don't care how great the water molecules are being scraped off if there's a lid on the tunnel you're not going through now not only can you have gated channels you can have gated channels that open depending on certain stimuli so if you flick the channel like apply a mechanical stimulus to the channel like my small people do to each other's heads you will actually open the channel and then you can imagine that you can't get in you can get in and we can actually send messages that way okay channels are so cool if you have a ton of channels in your cell membrane and you open them all up you can imagine that diffusion can actually happen superfast through a channel I love that so much now I mean carrier proteins are equally as coolest channels so let's go talk about carrier proteins next