bro i really need to get back into the group dude like the thing is i really cannot record on any of the weekdays so i'm basically limited to one video per week or i have to record a little extra on the weekend which i'm gonna try to do okay i'm trying to go for two videos a week we will make it as you can see i've literally reached that point in senior year where i just don't care about anything including my hair so you guys get to deal with this epicness okay but today today we are doing something extremely cool and that is talking about biology okay nobody wants to talk about anything other than biology biology is life okay there's nothing there's no dispute about that hello everybody i'm kara and today we are talking about unit 4 of ap biology cell communication and cell cycle and thankfully for me and for you guys this is one of the easiest units in the world this one is like hecka chill so let's just get into it all right so the first thing we're going to talk about is mechanisms of cell communication oh my god cells communicate that's great and basically the first way they do that is by direct contact so basically this is where two cells are touching so there's a couple ways this could happen but the two that you should just know about right is like you can either have like two cells that are like touching like this and they have like gaps in them that allow molecules to pass through and that's how they signal to each other they send some signaling molecules through this gap and hooray this cell tells this self i'm gonna go get myself a sandwich and then the other type is cell cell recognition so let's say that this guy's bob and this guy is like sam or something and bob wants to know who sam is so basically this cell has a bunch of proteins on its surface and this one has a bunch of receptors and when like this molecule binds to this receptor bomb knows that the other guy is sam i mean obviously cells don't have names i mean we don't know that but basically the idea is like receptors on one cell bind to molecules on another cell and that's how they recognize each other and that's how they communicate so either you have junctions that allow molecules to pass from one cell to another or you have like receptors binding to molecules on a different cell all right now the next one is local signaling so now if you don't want to touch people right like this is a pandemic we can't touch people like this that's like nasty we actually need local signaling so basically this is where they don't actually touch but they send messages over short distances so then we've got two cells here they're socially distant six feet apart no i'm kidding and basically if this cell wants to tell this cell something it releases a bunch of molecules called rho lo what local regulate and then these local regulators diffuse over and they bind to receptors in this cell and this cell gets the message so it's basically like the cellular equivalent of passing notes and this type of signaling is called paracrine signal and basically the one thing you should remember from this is that paracrine means local okay so if you ever hear paracrine the first thing you should think about is that these two cells are close together and it's just diffusion taking notes from one cell to the other another specific example of this is like when you have synapses right like there's a beautiful axon that looks really weird looks like a mushroom but it's okay and basically it connects to the dendrite of another neuron so essentially what happens in a synapse basically the connection between two neurons they release neurotransmitters and these diffuse and then the cell gets the message epic synaptic signaling there was an ap question on this so it's kind of important you know that synaptic signaling it's kind of easy to remember because synapse are like literally like really close together right so it makes sense that it would be local signaling and then you have to know that local associated paracrine very cool now it's not always practical to like hand out notes to whoever you want to communicate right like if you have a friend in china you're not gonna hand down the note from like people until it gets to china it's not gonna work okay so when cells decide to send notes to their friends in china this is called long-distance signaling so basically this is just your endocrine system the big bad boys who secrete hormones and yes those are the things that call it puberty okay you can thank your endocrine system for roasting your vocal cords okay so essentially the idea is that this cell releases molecules called hormones into the bloodstream and then the the bloodstream carries it all over the body right and that makes sense right if you want to get it to everywhere in the body you just put it in the bloodstream and everything needs to get blood in order to survive right you need oxygen to get to your cell so the way it works is it puts the signaling molecules which we just call hormone it puts it in the bloodstream and the bloodstream just takes it everywhere very cool stuff which is why it makes sense that long-distance signaling has to do with the bloodstream so whenever you hear like oh the cell is putting something in the bloodstream and then the bloodstream is taking it to some other part of the body then it's always long distance signaling and whenever you talk about hormones or stuff in the bloodstream it is endocrine okay endo in the bloodstream very epic so one way you could distinguish between endocrine and parapine is like let's say that you're you and your neighbor are like right next to each other right you don't need to go to the road move over like a little bit then go to your neighbor's house right paraphrasing is basically outside of the road so it's para like paralegal right like outside the law paraprime means that you're like outside the road endocrine on the other hand is in right you're inside the bloodstream and that's how you're gonna take it all across the globe okay and that's how i remember it it might not be very scientifically sound but it works okay it works that's all i'm going to say andre we are done with cell communication no i'm kidding but now once these molecules get to a cell they actually have to do something with the molecule otherwise what's the point of communication that's like me talking to you and you guys just staring blankly at me hearing the words that i say but not actually doing anything with them which is completely possible but i just like to believe that you guys are paying attention okay so the concept of signal transduction so basically you got a cell a molecule wants to communicate with it right some other cell sent in a molecule and it's like okay what do i do with this so basically what happens is the molecule binds to a receptor now the receptor could be outside the cell it could be inside the cell whatever but essentially this binding of the molecule to receptor has to trigger something in the cell for it to actually mean anything so the basic concept behind any type of signal transduction is when does a molecule bond right like let's say that it moves in there it binds really nicely to that receptor i don't know how i delete it half the receptor but it gets binded and the receptor gets activated now what the receptor does is it activates a protein on the inside of the cell which activates another protein inside the cell which activates another protein until you finally get like some cellular response and how does activation work in biology that's right you add phosphate so then this guy phosphorylates this guys that this guy's the epic p now and then this guy phosphorylates that guy that guy has the epic p and hurry we get a bunch of proteins activated just by the molecule binding to that one receptor and this as you might expect biology has very common sense terms other than phosphoryla which is a nasty term but this is called a phosphorylation cascade since essentially a molecule binds to a receptor the receptor phosphorylates the protein the protein phosphorylates another protein and then so on and so forth until the thing you want to activate is activated so why don't we get a little bit more specific okay what exactly happens so for specifics we first got to talk about the different types of receptors right so first off hydrophilic versus hydrophobic let's think about this for a little bit where would the receptor be for a hydrophilic molecule well it turns out that the inside of a cell membrane is hydrophobic like what so how is the hydrophilic molecule supposed to get past that nonsense so since hydrophilic molecules cannot get through the cell membrane because they love the water but the inside of the thumb rain is like the opposite of water they can't get through the cell membrane so hydrophilic guys people who like water who don't like the inside of a cell membrane they can't get through this nasty hydrophobic part over here but then like hydrophobic guys they can just pass through easy peasy lemon squeezy because the hydrophobic part doesn't bother them at all so that means that the receptors for hydrophobic molecules are on the inside okay that is the receptor and then let us talk about the specific types of receptors now this is like really not that important okay like i don't know why teachers even bring this up but like i'm just gonna briefly go over it because just in case it happens okay very unlikely that you're gonna know this but just in case so the first part is the gpcr or the smg gpcr so g-protein-coupled receptors okay so essentially all this means is that you have a receptor and it's coupled with the g-protein so basically what happens is a molecule binds here the receptor activates the g protein that's attached to it so now this guy has a phosphate group and now the g protein could go do whatever the heck it wants and start up a cascade of phosphorylation very nice and then there are rtks or receptor tyrosine kinases and basically you have receptors that's a receptor you got another receptor and when molecules bind both to the receptors these two guys come together and they phosphorylate a bunch of tyrosines basically a kidney is something that adds a phosphate group so it makes sense right like a receptor right you receive the molecule then when they're activated they like add a phosphate to tyrosine so tyrosine just uh amino acid on a protein so essentially when the receptors are both binded they come together and they activate a bunch of protein the main difference between these two is that receptor tyrosine kinases activate a ton of stuff and then the last one is a lot different from the other ones the other ones activate other proteins right well these guys are like not cool and they decide not to activate other proteins so essentially you got like a receptor and it actually is linked to a channel so these are called ligand-gated ion channels and it's stuck in the plasma membrane and when the molecule binds here it lets through like ions right so maybe it's calcium it lets the calcium in or out of the cell typically in okay so nothing is getting activated here but it's letting ions come in and sometimes these ions could actually function as activators of a protein like calcium two plus is an example of an ion that does so why don't we talk about calcium a little bit more because you know it makes your bones strong that is the reason calcium is what is known as a second messenger okay so basically what happens as i said before the ligand-gated ion channels don't directly activate like proteins right but they let in a molecule that does and these molecules that like don't directly activate proteins but like are created after a receptor is activated are called second messenger because instead of being the primary messenger which is like the molecule that activates the receptor they're a secondary messenger so the receptor tells the cell okay fire off the other messenger which is calcium which will then go tell other proteins to get activated so essentially the way it works is you have your receptor and then you have a molecule bind and then it tells your cell oh make some calcium happen so then it like has calcium now the calcium goes everywhere and then it activates the protein here and activate the protein here and activate the protein here very cool stuff what are other examples of second messengers you got calcium two plus you got c-a-m-t you got c gmp whatever there's a bunch of second messengers just know that like they typically start with c's right and their main function is to spread the word like one molecule binds to this receptor but there might be like a ton of second messenger that goes spread out through the cell second messenger right they're not the first messenger okay so why don't we just go through a really quick example of adrenaline just to like put this all together okay like if you didn't understand anything that just happened you're gonna understand now i promise so essentially what happens is you got a receptor and this is a g bruh why are drawing receptors so hard holy moly what the heck okay so like that that's your receptor there we go and this is a gpcr it's coupled to a g protein so essentially what happens is a molecule binds and this guy gets activated now what happens is that this g protein goes and activates another enzyme called adenylyl cyclase holy moly i spelled it right the first time now that is crazy now general cyclase is the thing that makes camp so this thing creates a bunch of c amp molecules right c a and p c and p c m p and each of these molecules goes and activates another protein so these second messengers uh spread the message of the first messenger and go and tell protein kinase a to get activated and basically a kidney is something that phosphorylates other proteins so as you might expect it phosphorylates other proteins holy moly that is crazy this is such a creative name not gonna lie and then this activates a ton of other proteins which eventually break down your glucose okay so that's why adrenaline just by reaching a receptor actually ends up breaking down your sugars so that you can use it for exercise or like when you're stressed it lets you use your resources by breaking down the like storage sugars you have all right so now what happens if we want to stop the signal okay you don't want a smoke alarm going off in your house and just going on the whole day those smoke alarms are the stupidest thing that have ever been made if they didn't stop i would literally go insane but basically the way we stop these signal transduction pathways after they've been started is by like some proteins called phosphatases so we know that kidneys is like activate stuff but then we got phosphatases that stop stuff so these guys put phosphate on which makes sense right kin like kinetic energy right you want to put energy on them and then you got phosphatases which are basically like phosphate tasers you know they they like roast the thoughts okay i don't know what i'm saying but basically these guys take off the phosphate and deactivate the pathway now why the heck do we even care about these boring kidneys phosphatase signal transduction pathways it's because these things actually cause diseases right like the best example i know is like cholera and basically what happens is that a g protein is locked in the state that activates this pathway and the pathway is telling your cells to secrete water so essentially your cells are constantly secreting water so you get really really bad diarrhea okay diarrhea is just pooped with water so essentially if you have cholera like this pathway just keeps telling your body to create more water even though your poop is super wet we're going to add more wetness to it epic i don't epic so yeah that's why g proteins are relevant you don't want wet poop okay all right so now the next thing we gotta talk about is cell junctions okay and this is going to be pretty straightforward right you basically got desmosomes which are when you have two cells and you basically attach them with like a rivet i literally did not know what a rivet was until i read campo but basically we did a lot of riveted right like i mean the pictures don't really make it that clear but basically the idea is you have like a screw on one side and then you like close the screw on the other side so it basically holds two metal sheets together so essentially the idea is you have like a screw head here you have a screw here here and it keeps the cell from moving apart then you got gap junctions which are exactly like the sound you basically have your two cells and you basically got a pathway through it there's a gap right there i don't feel like you're racing that tiny little thing but essentially you could believe that molecules would just pass through the gap and then type junctions are literally exactly what they seem okay you know why don't you guys take a guess at what a tight junction is oh they're two cells tightly packed together holy moly how did you guess that holy broly that is insane so essentially they're super tightly packed together it's so tight that water can't get through so basically this is pretty useful for your skin right because you don't want water to just penetrate randomly into your body so that's where you would have tight junctions all right basically the way to remember it is that two of them are super self-explanatory and then the third one that's whatever's left like who the heck cares about rivets so that's why decimators are ribbons okay so now we just got to talk about cellular responses so we know how the cell actually like transfers uh reception into like activating proteins but what is the actual response of the cell so essentially that idea so exactly the biggest picture idea of this like section is homeostasis right if you understand homeostasis you are gucci game okay essentially this is just balance right you want to make sure that everything's at the right place where you want to have the right temperature you want to have the right ph you want to maintain everything in a certain space because i don't like being a fried human okay 105 degrees fahrenheit is way too much for me all right fine maybe i'm spoiled but i don't like being fried human fried chicken is fine frightening is not okay and basically the main way that this works is something called negative feedback and like the most obvious example like if you're becoming a fried human right if it's way too hot your body responds by trying to make you cooler right so if you become too hot you release flat which is supposed to take away the heat from your body and put it in these water molecules that are on this on your skin other examples if you're eating too much and your body wants to like keep your food intake like at a certain level it basically makes you full right it makes you want to stop eating so that's another example of negative feedback basically it makes you stop something that's taking you above your certain like threshold right so basically the general like concept of negative feedback is like let's say your body wants to keep you right here right but you're just being a troll and like running away from the point that your body wants you to be at that essentially what your body tries to do is just bring it back right like if you're too hot it wants to make you cooler if you're too cold it wants to bring you back to being at normal temperature now the other thing is positive feedback now this one is not as intuitive but basically it's the opposite right if you're going this way it amplifies that like another time now this doesn't make sense that you're getting too hot right if your body just makes you hotter you just die okay that that's not a good idea but essentially this is used in places where you need to amplify your body's response the example they give in the book is childbirth right like when you're pushing a baby out of your uterus right you want to make sure that your uterus is contracting like extremely hard right so essentially when your uterus contracts it releases oxytocin which causes your uterus to contract even more and basically that pushes out the baby that was extremely simplified the way i was looking at it but basically the idea is in certain cases when you need to amplify your response positive feedback is where you go but negative feedback means you counteract the change right you're taking a positive change you're taking the negative of it and you're pushing it back and basically that's all you got to know about cellular responses now the book does talk about something called apoptosis and this is actually one of the most important things even though it's not tested that much on the ap bio exam because it causes cancer okay the lack of apoptosis is what causes cancer so what it is is programmed cell death not programmed but you get the idea so basically the idea is if a cell is no longer useful our body just kills it but the idea is if non-useful cells are not like allowing themselves to be killed then they're just going to create this tumor and that's what causes cancer right like if the body can't kill cell they're being useless and these cells are just left to like replicate that's what happens in cancer honestly you don't really have to know much else like obviously lysosomes are what break down the dead cell but i literally did not much else to know about it for the ap bio test all right we have finally reached the funnest section of all of biology the cell cycle i know it's so fun it's crazy fun it's the most fun no it really isn't it really is not okay cell cycle so basically your cells have a genome right you got like dna in your nucleus very cool stuff and essentially this dna is stored as chromosomes which you see have exited usually now the reason why they look like x's is because they're actually two separate things they're basically two lines but you connect them and that's why they're put as x's so each one of these lines is called a sister chromatid because each arm of this chromatid is exactly the same that's why they're called sisters they're literally the exact same thing but they're duplicated twice and we will see one and then the part where they cross over is called the centromere where they're connected right the center of the x centromere makes sense now chromatids are the individual thing right like a cro like it is like a mini part of it but when you put them together you put two chromatids together this whole thing is called a chromosome and then if you use your imagination you could see what these two things are called arms of your chromosome and that's basically all you have to know for the shape of a chromosome now how does a human genome look now you've probably seen this it's called a karyotype but basically you have like all your chromosomes you got like two x's here you got two x's there and you got one two three all the way over to like 46 whoops 23 23 is what i meant so essentially humans have 46 chromosomes and basically 23 pairs of chromosomes and the idea is you get one from your mom you get one from your dad so now this is a somatic cell right you basically got one from your mom one for your dad you got like a pair of each right and this is what normal cells have uh normal cells are called autosomes or somatic cells now what you want to have babies okay when you have those sperm cells and egg cells going on they have actually half right because if you had a full cell plus a full cell make a baby then you're gonna have a double cell and you don't want your baby to have twice as many chromosomes as you okay that is not a good idea so basically when you want to make the baby stuff you gotta have games okay and these only have one of each chromosome all the way up to 23 of these bad boys all right so the next unit talks about gaming and like sexual reproduction and all that but in this year we're just talking about normal beautiful 46 from some self okay we don't have to worry about all that nonsense so definitely the cell cycle is just the lifetime of a cell right it like lives it grows and then it divides so eventually the living and growing part is just called interface and then the dividing part as you probably know as your little ptosis mitosis now oh shoot i literally it mine since mitosis divided now interface itself the living and growing part is divided up into three phases you got g1 s and d2 g1 and g2 growth phase g for growth s for synthesis so in g you might expect it just grows right but then in s you're synthesizing new dna okay so grow duplicate dna and grow again so essentially at the very beginning of your cell cycle you start with only one chromatid for each chromosome right so you still have one from each of your mom and pop right your mom and pop ones are two separate things but then during the s phase it duplicates each thing exactly and remember sister chromatids are attached to form a chromosome and sister chromatids are identical so when we say duplicate it essentially just means turn these lines into exits so at the beginning of space these are lines and after s phase these are x's now interphase is like 90 of the time right like nobody spends like 50 of their time reproducing that would be kind of sad but the other 10 of the time is been dividing into new cells so how the heck did that work so we're just going to stick with six chromosomes so i don't kill my hand trying to draw like 46 chromosomes that would be scary but basically we start in prophase okay and basically prophase is just the start of mitosis so now we're talking about mitosis so i've probably raise this mitosis now in order to play around with these chromosomes the cell can't deal with a stupid nucleus membrane so this gets deleted and essentially just stuff gets uh set up for mitosis to happen right these chromosomes uh get condensed so they're easier to work with like um like the things that are gonna pull the chromosomes around get pushed to the side everything gets prepared prophase for preparation phase very cool that's not what it stands for but that's how i remember it then we got metaphase and meta kind of means like in the middle kind of not exactly but meta kind of the middle so basically what happens in metaphase is that each of the chromosomes gets attached to both sides right so essentially like this connects to one arm of the x this connects to the other arm of the x and that happens for all the other ones why don't we just go with three three is easier okay and then like that and essentially they're getting pulled on both sides so they get pulled right to the middle so that's why it's called metaphase right you're pulling them to the middle and now you're at the metaphase plate the line that divided the two sides then we go into anaphase basically now we get to see why we have those x's in the first place why do we need x's that's because one has to go to each side one part of the x goes to each side of the thing now this probably doesn't make sense because we've got to have a multiple of two otherwise we want to have one from our mom and pop so we gotta have two all right there we go all right so now in anaphase these guys go to separate sides so essentially since this um this guy is attached to this one uh this guy gets pulled over this way and essentially we have all the single lines getting pulled over here and we got the other side doing the same thing and then uh i don't have space for telephase but the last phase is called telophase basically the way people remember it is p mat so like after a you got telophase and what happens is the cell starts pinching like that very pinchy and the nucleus starts performing around like these boys so you got your chromosomes here you got your chromosomes there and right it's starting to look like two cells so now after all pamt is done we actually got to finally split these boys apart so we got two daughter cells okay so to do that all we got to do is cytokinesis right you're breaking cytoplasm the inside of cells into two parts kinesis break them boys so essentially what happens is like those two things that i was talking about earlier they also attach to each other so essentially they push each other out so now that they're really stretched out they basically take a ring around the middle they squeeze the ring like a drawstring bag they just slam it down and then these two guys pinch off right there very cool stuff so now we got our two things each with a single thing uh in each one and this is exactly how we said it would look before s phase and guess what it's going to look like after esp8 each one of them is going to become an x again and we can repeat mitosis again very epic stuff by the way this thing that ring that i was talking about is called the cleavage furrow which is a kind of interesting name but this like concept of like squeezing the two cells and pinching them apart is called cleavage okay so you can probably see right we started with like two n chromosomes right we had normal diploid cells right you have like one for your mom one pair of pop and then it divided up into still two ends because you still have one from your mom one for your pop except it was only the lines right like you don't have your sister chromatid you only have one of them and then after f phase you still have one from your mom one from your problem but it just gets duplicated in that one x so it goes two into 2n so you're just duplicating yourself exactly as they are no change okay the last thing we got to talk about before we're done points okay and basically this is just where between stages your cells just make sure that everything is okay before going on to the next stage right like if your dna is messed up your cell's not going to be allowed to divide and this basically happens for every stage right you got like a g1 check you got a g2 check you got an s check you got an m check there's all kinds of checkpoints okay and basically they just make sure that the cell cycle is running as it should and essentially what happens when these checkpoints don't work is cancer like if your cell is just allowed to keep dividing over and over and over again without any checks and balances is this gonna make a really massive tumor same concept with not having apoptosis this is what causes cancer all right that's all we got today that was epic okay this is one of the easier like units i think it's one of the more interesting ones too but i hope you guys enjoyed it hope it was helpful thank you guys so much for watching as always if you enjoyed the video leave a like and subscribe for more thank you guys so much for watching again and see you guys next time