hello bisque 130 this is the beginning of recorded lecture 31 starting off chapter 10 on cell reproduction so again we're getting bigger picture now the first uh several chapters are about you know molecules and organel and stuff now now we're talking about cells and how they make more of themselves so not for the first time and certainly not for the last time we will be when we talk about cells comparing and contrasting procaryotic cells and eukaryotic cells uh because the way they do cell division is going to be different so before we even talk about cell division though I want to give just a little bit of background about the genomes Within These different types of cells so let's start by talking about procaryotes the procaryotic chromosome their DNA their genetic information their genome you can see here it looks like a big old squiggly line remember these things do not a nucleus so it's just floating around the cytoplasm if we wanted to isolate this genome we would see that it's actually a circle it is a single closed Circle that just looks squiggled up when it's you know wrapped around like this so the procaryotic genome and the term genome in fact is in the key terms key terms define genome as the total genetic information of a cell or organism the procaryotic genome is a single DNA a Macro Molecule uh and it is a closed Circle in contrast ukar plants animals fungi always more complicated have not just one chromosome uh but a bunch of individual chromosomes the exact number depends on what species of ukar you're talking about uh eukariotic chromosomes uh this is human uh so humans have 23 uh different chromosomes but again depend dep on the ukar exactly how many we're talking about uh but yeah importantly it's uh it's plural it's not just one like within procaryotes uh it's a bunch so eukariotic genome consists of several DNA macr molecules several of these chromosomes humans I'm not a fan of making you memorize a bunch of just specific numbers but I mean come on we're humans we should know this um humans in particular have 23 different chromosomes and this allows me to introduce a couple of other terms here if we go back to this figure we could see yep there's chromosome 1 chromosome 2 chromosome 3 chromosome 4 and so on but we see two of each of these and indeed we have two different versions of chromosome number one two different versions of chromosome number two two different versions of chromosome number three and so on the term for this is diploid the key terms define diploid as a cell nucleus or organ organism containing two sets of chromosomes however it is worth noting since we're just putting out terminology here there's also the term haid so there are some cells uh we'll talk about in the next chapter actually uh and some organisms like some uh some weird protests some strange mosses uh there are some organisms that are not diploid but haid haid reading from the key terms a cell nucle or organism containing one set of chromosomes so we're actually going to use these terms several times in different chapters throughout this quarter so you should be familiar with them now uh diploid means two copies of each chromosome haid would mean one copy of each chromosome the other important thing about eukaryotic chromosomes which should be review from an earlier chapter is that the DNA is not just a naked Helix like it is within procaryotic cells but it is wrapped around these proteins called histones to form structures called nucleosomes so this is a nucleosome it is DNA wrapped around a histone if we take a bunch of nucleosomes together we form something called chromatin so yep we can see naked DNA here's a nucleosome here's a bunch of nucleosomes together we call all this stuff chromatin so in summary uh again these are not defined in the key terms they're sort of defined in this sentence itself but I underline the important terms uh in this statement the DNA in the UK carotic genome the DNA double helix is wound around histone proteins to form many nucleosomes which all collectively are referred to as chromatin and again none of this happened in procaryotes this is a ucareo thing the last thing to point out as far as UK carots go is our chromosomes are linear they are not circles like procaryotes they are um individual sausages uh you know individual lines there's one end there's another end uh eukaryotic chromosomes are not circular they are linear okay so again this is just some background about the chromosomes themselves now we can actually talk about the topic of this chapter uh cell division so of course we're going to talk about procaryotic cell division and eukariotic cell C division because they are simpler let's start with procaryotes so the process of procaryotic cell division is called binary Vision it's just the specific name for cell division going on in procaryotes so you hear binary Vision your brain should immediately understand this is a procaryotic thing so we could uh we could break this down across several steps so step number one of binary fion is d DNA replication so I did say just a few slides ago that these procaryotes have one chromosome and that's true most of the time but if this cell is getting ready to divide to split into two each of those resulting cells is going to have to have its own chromosome so the first order of business here in binary fion is to duplicate that chromosome to replicate that chromosome the exact details of how this is done uh is going to be the topic of a later chapter but for now I'm just going to say step one of binary fion DNA replication now the other thing that each of these resulting cells is going to need is it's going to need cytoplasm it's going to need space they're going to need to be you know the correct size so next the cell is going to get bigger uh we call this elongation you may notice you know the the two chromosomes here these two circles but we also notice some green dots here now there are a lot of proteins involved in making all of binary fision happen so I'm I'm calling out and the figure is calling out one of these proteins in specific but I just want you to understand this is not the only protein doing a job here it's just one of the most important ones uh so this these green dots are meant to represent something called ftsz um a funky way of capitalizing it it's how microbiologists like to name proteins we'll see a couple more examples of this uh later in the quarter uh but yes during elongation these ftsz proteins start to move towards the center of the cell we'll see why soon enough so in summary step number two cell elongation and ftsc protein moves to the center of the cell now we know what's going to happen Happ at the end here by the time we're done with this we're going to cut this cell in two and we're going to have two cells um because we don't want to damage the chromosomes if we're going to split this cell in half we want the split to be down the middle and we want these two chromosomes to be nowhere near the middle we don't want them accidentally getting cut in half as the cell you know Cleaves itself in two so during this next step these chromosomes are going to be moved to opposite sides of the cell and you can start to see this green ftsz protein forming a ring so again this is a flat image but remember cells are are threedimensional this is a ring sort of pointing out at you and going back into the cell specifically at the middle of the cell so step three chromosomes move to opposite sides of the cell this ftsz protein many copies of it form a ring there in the middle of the cell next we're g to start building a wall remember procaryotic cells have a cell wall so if you're going to split the cell in two you got to build a wall right down the middle we call this wall a septum and it's ftsz that is directing the formation of this again ftsz isn't building this peptidoglycan polysaccharide it's not building this septum it's sort of the central coordinator ftsc is telling all these other enzy sles and things that you're supposed to build this wall this septum here in the middle not right here not right here not across the middle like this specifically in the center here that's why if we can go back a few slides it was so important that the ftsc goes to the center and forms a ring at the center because we need to have this wall made at the center so step four ftsc protein directs the formation of this septum a dividing cell wall in the middle or center of the cell and uh finally walls in place now the plasma membranes just need to pinch off from one another and we have what are called two daughter cells a weird kind of terminology here you have one parent becoming two daughters there's no difference between these two so it's not like one is the original Parent and one is The Offspring nope one parent becomes two daughters that's just the terminology so step number five the cell pinches into two forming two identical daughter cells and here's the slide showing all these together uh if you want to look at it this way so that was binary fion that was the procaryotic way of taking one cell splitting it into two ukar Nots are as always going to be a bit more complicated in ukar cell growth and cell division so both parts of this getting bigger and then Divi you know splitting in two are part of a complex what's called cell cycle so I I love this figure as a great overview of this entire process uh so this is a a circle that's just sort of ongoing but if we want to hop in uh at the beginning of this circle we would hop in right here in what is called G1 capital G sub subscript one so yeah I'm double underlining UK carotic cell cycle because you know these several stages are going to be underneath this uh starting with G1 uh the G stands for Gap so this is technically Gap phase one what happens in gap phase one well boring background stuff uh growth and accumulation of resources again the cell's got to get bigger if it's going to split in two and as we'll see it takes a lot of energy it takes a a lot of raw materials to go through the process of cell division so just mustering your resources getting everything ready is an important part of this this chart is supposed to be drawn approximately to scale so this slice of the pie looks like it's uh it's the biggest uh that is intentional this is the longest stage of the UK carotic cell cycle again just boring background stuff I don't even have any pictures of cells in G1 uh cuz you can't really see what's happening here they're just getting a little bit bigger and getting their resources together okay after G1 we have S phase the S stands for synthesis uh synthesis means building something or constructing something uh what are you building well DNA so even even though this is a lot more complicated than procaryotic cell division than binary fishion at the end of the day the same basic stuff is going to happen in our cells we're going to replicate our DNA we're going to move the chromosomes to opposite sides and we're going to split the cell in two that's basically what's going to happen so uh it just has different names to it so yeah sphase synthesis replicate the DNA which does mean if I can I can go back to this we've got as humans 23 chromosomes uh two copies of each so that's a total of 46 chromosomes after S phase our cells are going to have what's 46 * 2 uh 92 total chromosomes in these cells after they have completed this S phase so yeah every single one of these chromosomes is going to be replicated during s uh it is also worth noting a sort of a call back you may remember this structure from inside of the cell something called the centrosome uh which contained centrioles which contained microtubules I introduced this in several chap CHS ago uh this was an animalon structure and it is during this S phase this synthesis phase that specifically in animals you get a replication of this centrone so we're going to have two of these in animals after we've finished s so yeah replication of croome contains centrioles which contain microtubules we'll see the job of this soon enough but it's worth noting that it's synthesized it's duplicated here in addition to all the chromosomes Okay so we had G1 s next is G2 so Gap Phase 2 this is where we get replication of some organel stuff like mitochondria chloroplast lomes peroxisomes depending on exactly what type of cell we're dealing with uh but yeah some organel are going to get replicated here and just further growth and accumulation of resources just sort of another Gap don't have a picture of a cell here because yeah most of this is not something that you can see uh now you may have noted that you know this Arrow here that called this interface uh but it also called this interface but it also called this interphase interphase is kind of an umbrella term that includes these first three stages so collectively G1 s and G2 are all referred to as interface each of these three are part of interface which is just like the getting ready phase of the eukariotic cell cycle so yeah this just refers to to all three of these okay next we have something called mitosis and even though this is a you know slim slice of the pie here there's actually a lot of complexity to what's going on during mitosis so we're going to break down this slice of that pie uh itself into five different stages so mitosis has several steps these stages are going to be prophase Pro metaphase metaphase anaphase and tase and I will write those out as we come to those slides but this you know sort of acronym is is worth uh worth looking at uh because it's important to not get these things mixed up with one another to know what happens in each of these phases if you can remember PPM a you could remember the order of these phases prophase Pro metaphase metaphase anaphase tilas phase that's the order so okay uh let's look at prophase zoom in on this um what happens during prophase is that these chromosomes which are already wrapped around nucleosomes they're already packed up are going to start to pack even more tightly the chromosomes are going to condense and I I like the term become visibly distinct uh so under normal circumstances in the cell even under a microscope uh you can't really see the individual sausages but after prophase and during prophase you start to be able to see and again this microscope image it's difficult to see it's might kind of like the cartoon better uh you can see the individual sausages you're just going to they're just going to condense up as much as possible the other thing that's that happens during prophase and you can kind of see this here the nucleus breaks down so nucleus obviously a very important organel it protects the DNA but we know what's going to happen to these chromosomes it's like I said essentially the same thing that happened in binary fion we got to move them to opposite sides and split the cell in half well we're not going to be able to do that if they are contained within a nucleus so during prophase we break down the nucleus and while we're at it we're going to break down the ER and GGI as well these structures are associated with the nucleus so we're going to get rid of all these things so nucleus gold prophase nucleus GG and er break down chromosomes condense they become visibly distinct and something called the spindle apparatus forms we can see it over here this sort of blue spider looking thing I'm not going to say more about spindle apparatus now we'll see what it does in just a second which is PR metaphase so during prometaphase here we've got the spindle apparatus extends out its microtubules to attach to these chromosomes so prometaphase microtubules part of that spindle apparatus attach to sister chromatids okay so here's where we need to zoom in a bit so yeah we can see that these are two chromosomes here uh two sausages let's zoom in on these so the these two chromosomes are identical to one another they are exactly the same this is not talking about these two chromosomes these two chromosomes are not exactly the same and we'll get more into you know the implications of this in in some of the later chapters these two are not exactly the same these two are not exactly the same these two are not exactly the same these two are exactly the same because we just had DNA replication during S phase every single one of those 46 chromosomes has an identical partner these pairs of identical chromosomes are referred to as sister chromatids I don't know why they call it a chromatid and not a chromosome but in this context when they are partnered up like this they are called sister chromatids and in fact there's a definition of this in the key terms the key terms define sister chromatids as two connected identical copies of a chromosome so that terminology out of the way we can see microtubules part of that spindle apparatus attaching to the sister chromatids at a specific point called the kineticore spelled kinea chore uh but this is the kinetic cor it is very important that these microtubules attach at the kinetic cor because again we know what's going to happen eventually they're going to get pulled apart from one another they're going to move to opposite sides and if we want these microtubules sort of tugging these things apart we don't want some of the microtubules attached up here and down here and down down here that would rip the chromosome or the chromatid apart we want to make sure that all the microtubules attach at these specific Central locations which are called kinetic or so again in summary microtubules during prometaphase microtubules attached to the sister chromatids at specific points called kattic cores okay so they're going to get pulled apart from one another but there's actually one more phase before we do that pulling apart we have to make sure that everything is lined up nice and neat and orderly in the middle of the cell again during Pro metaphase these connections were made the chromosomes were still kind of loosely just floating around where the nucleus once was metaphase is where everything lines up in the middle every single chromatid is positioned to go to one side or to the other side two sides here so this is metaphase cister chromatids align at the center of the cell positioned to move to opposite sides of the cell now we finally do what we know is going to happen the whole time they're pulled apart and go to those opposite sides so this is anaphase uh these sister chromatids are broken apart as these microtubules shorten moving all these chromosomes either to one side or to the other side and because every single one of these chromosome pairs was they were identical copies that means this set of chromosomes is exactly the same as this set set of chromosomes again just like binary fision we are making two identical daughter cells by the time we're done with this whole thing so anaphase cister chromatids are split apart and this spindle apparatus and its microtubules pulls these things to opposite sides of the cell PP m a t so after anaphase must be T teal phase here's where things start to go back to normal the chromosomes are going to relax they're going to decondense you can see them starting to get kind of fuzzy and hazy you won't be able to see the sausages anymore under a microscope we also see during Tila phase the nucleus beginning to reform the nucleus and the GGI and ER but it's happening X2 this is going to be a cell with two nuclei each one with a full set of chromosomes each one with its own ER and GG surrounding it so tase chromosomes decondense nucleus gger reform X2 we got two of these so importantly and this trips a lot of students up mitosis is not cell division look at this we started with one cell we end with one cell mitosis is not cell division mitosis is part of the UK caronic cell cycle and we're going to split this in two in just a second but this process itself mitosis is dividing the nucleus mitosis is a process of nuclear division we start off with one nucleus it's got replicated chromosomes by the time we're finished with mitosis we have one cell but there are two nuclei each with a a A non-replicated or you know complete uh set of chromosomes we've divided the nucleus we have not divided the cell so importantly the stage that comes next is not part of mitosis um again mitosis is PP matat this next thing comes after mitosis but it is not part of mitosis the next stage after mitosis is called cyto canis and uh yeah cell pinches in two uh and then you end up with two daughter cells not uh too much to this um in an animal cell where there's no cell wall this involves the formation of something called a cleavage Furrow which just has to pinch the membrane in two in plant cells which do have a cell wall uh you have to build this wall down the middle more similar to what we saw with bacteria you build this cell plate down the middle and then you pinch off the membranes but either way you're going to end up with two identical daughter cells as you finish cyto canis so in summary uh in cytokinesis the cleavage Furrow in animal cells or the cell plate in plant cells separates the cell into two identical daughter cells and again here's a good overview but don't get confused prophase prometaphase metaphase anaphase telophase these are mitosis cyto canis not part of mitosis it comes after mitosis uh confusingly we can lump these two together so there is the term mphase just like interphase referred to g1s and G2 the term mphase collectively refers to mitosis and cyto Kinesis so just another another term that gets used describing the eukaryotic cell cycle and again I really like this slide uh as just a good visual overview for all of these steps in the order in which they occur now there is actually one more stage that we could talk about and if you're squinting hard at this and trying to search for it uh it's actually not on this figure there's one more stage that is technically not part of the cell cycle that's you know why it's not part of this figure but it's a very very important stage this stage is called g0o capital G subscript zero and it's not part of the cell cycle is essentially an offshoot of the cell cycle cells in g0 Finish cyto Kinesis and then instead of going back to G1 and starting the whole thing again will go off and be g0 instead so again this is kind of an offshoot not technically part of the cell cycle g0 is also o known as resting phase uh I I really don't like that term but it is the term that that is used and I'll explain why I don't like it uh but g0 also known as resting phase uh is not part of the cell cycle it's an offshoot after cyto canis but before G1 so what's going on in g0 well the cells in g0 are not actively dividing that's why it's not part of the cell cycle if you're in g0 you're not getting ready to divide you're not you know accumulating resources you're not preparing or whatever cells in g0 h are doing nothing to do with the cell cycle that's why it's called resting uh but I don't like resting because it implies these cells are just doing nothing which couldn't be further from the truth cells in g0 are just doing their job whatever the job of this cell is they are doing it most of the cells in our body are in g0 uh your skin cells they're doing the job of you know secreting oils and and sweat and stuff like that they're doing their job they're not dividing they're in g0o your muscle cells they're Contracting when you tell them to do so uh they're not dividing they're doing their job they're in g0o cells in your liver neurons in your brain uh virtually all the cells in our body they're just they're not resting they're not doing nothing they're doing whatever their job is uh they they are in this g0 phase so it's very important in that respect and that most of our cells are not actively dividing there in this g0 so this is for cells doing their normal functions not getting ready to divide or doing any of this other stuff very few cells in the body are actively going through this cell cycle okay now let's talk about control and regulation so this is obviously a very complic ated process none of this magically happens on its own there is a lot of Regulation that occurs here to make sure that it all happens without any mistakes the cell cycle is regulated by internal factors so the cell has sort of internal checkpoints like pause like H am I ready to go forward should I continue the cell checks itself in three main points so there are three main cell cycle checkpoints uh which are shown on this figure so very similar to the last one but this is showing the checkpoints here the first of these is something called the G1 checkpoint and wouldn't you know it it happens in G1 near near the end of G1 the G1 checkpoint is checking for energy and resources for DNA replication and for damage to DNA so again just think about this logic uh if you're going to finish off G1 that means you're going to proceed into S phase where you're going to replicate all the DNA that takes a lot of energy to replicate DNA that takes a lot of raw materials a lot of nucleotides you don't want to start this process if you're not ready to see it through so the G1 checkpoint is going to check for this and is going to hold things up and wait pause that cell in G1 until it's actually ready to go forward cuz that's the other thing about DNA DNA replication there's no rewind button on this there's no pause button on this you got to make sure you're ready before you leap and it's also checking for damage to DNA we we'll talk more about damage and repair in later chapters uh but yeah you don't want to replicate damaged DNA that's a recipe for disaster so this checkpoint is also looking for damage and you're trying to fix it before you move to that very important step of replicating the DNA our next cell cycle checkpoint is called the G2 checkpoint which again I like these names uh is in G2 it's it's near the end of G2 and and what is the G2 checkpoint checking for well it's also checking for damage to DNA and this sounds a little redundant with the G1 checkpoint but uh here at this point it's been a long time since the last checkpoint you replicated everything you had some more growth we're about to head into mitosis and you do not want to have damaged DNA during mitosis you want all your DNA to be in proper working order before we start moving these chromosomes around so it's important to once again make sure that all this DNA is in proper working order no damage and if there is make sure it's repaired before you have the green light to move from G2 to mitosis and third is the m checkpoint which is in mitosis and you may think that the m stands for mitosis technically the m stands for metaphase because this m checkpoint happens during metaphase what we're checking for here is we're checking to make sure that all of these connections are secure to make sure that every single sister chromatid is attached to the microtubules part the spindle apparatus we know what happens after metaphase they're going to get pulled apart from one another if any of these chromatids are not secured to microtubules they will not get pulled apart and that would be really bad so we just con you know secure the connections double check all these Connections in metaphase before they get pulled apart in anaphase no no take Backes once you start going through this process so our third checkpoint is called the M checkpoint m stands for metaphase it checks that all sister chromatids are properly connected to the spindle apparatus now these three were internal checkpoints where the cell checking its own you know status of its you know proteins and its DNA and its energy levels and stuff like that the cell cycle is also regulated by external factors you know we got 40 trillion cells in our body for example uh they need to play nice with one another they need to make sure that they only divide when they need to divide so part of these external regulation is that cells need permission from surrounding cells to divide we don't want our cells just dividing because they can uh or because they have enough energy to we only want our cells to divide when we need them to divide and we're going to uh um you know send external factors hey this goes back to the last chapter this horrid figure again uh we're going to send lians that bind to this these receptors a big part of this gigantic signaling pathway is to control cell proliferation to to tell cells when they need to divide and when they don't need to divide so this external regulation is incredibly important in maintaining normal cell number and normal cell density we only need so many cells we only want to divide if there's actually a need for that division so cells are checking themselves internally uh cells are also being regulated by factors from the from the outside of the cell from from ligans binding to their receptors and none of this regulation magically happens on its own there are tons of proteins involved in signaling Pathways obviously and there are tons of proteins involved in all these internal checkpoints as well this is another one of those figures that you don't need to memorize or sweat the details on I just like showing something that really illustrates the you know the full complexity of everything that's going on here that there are tons of proteins involved in all of these checkpoint regulation things or or whatever uh yeah doesn't happen on its own many proteins involved in regulating the cell cycle okay we've got one more section uh on this chapter but I don't think I can finish it in the normal amount of time that I have so this is going to be the end of recorded lecture 31 I'll finish up cell reproduction uh in the next recorded lecture but y this is the the end of what I got for 31