Cell Division Part 1 Cell Cycle and Mitosis

so just for quick overview let's just go over again what we talked about chromosomes we know that no normal cells we have chromosomes we got from our mom and chromosomes we got from our dad so if we're talking about one particular chromosome like chromosome number one we got one from mom one from dad we call that pair of homologous chromosomes don't forget that we get one chromosome from each parent that is homologous chromosome they each have the same set of genes that they're going to code for except they have different versions of them quick overview diploid meaning two sets diploid cells have two sets of chromosomes one from each parent which already familiar with we also know that these cells that are diploid are going to be all of our normal body cells this would be our somatic cells so make sure you know that word right there cells that do not have two sets of chromosomes is there's only one type of cells it's like that is our haploid cells are haploid cells help one set that means if you're human you're haploid cells will have 23 chromosomes and there's only one type of cell in our body that will have haploid number of chromosomes and that is our for our sex cells for argument's karyotype what exactly is karyotype all the karyotype is is picture of all the chromosomes in an organism cell and they're usually arranged by size so if we look over here what we're looking at is human karyotype we know we have total of 46 chromosomes 23 from our mom 23 from our dad and we pair up the homologous chromosomes in karyotype or range from by size very last pair pair 23 will be your sex chromosomes so why do we need to know about the life cycle of cells well all cells aren't always dividing every cell has different life span so if you look at this chart you can see depending on what kind of cell you are you might live very long time or you might live short time and you may be constantly dividing or you may never be able to divide if we look over at our digestive tract cells right up top you see that most of them have life span of less about 10 days we're constantly using our digestive tract ripped straight from our mouth all the way down to our intestines so we can see that these cells are going to be constantly dividing our red blood cells replace about every 120 days that's why we can donate blood our white blood cells are little bit different we have different types of white blood cells some white blood cells are going to stay in our bodies forever holding important information about how to fight certain infections or viruses bacteria and these are what we call our memory cells so they can live very very long time however we have some short-lived cells that when you get sick the cell start dividing they fight off the infection after that they're done so they come about 10 hours the life cycle of cells consists of two major stage is the first major stage is what we call interface and that consists of three different parts we have g1 and g2 and you can look over here and see what's going as far as those different stages we come over here every cell is going to be spending time in g1 if your cells just doing what is normally supposed to do it will be in g1 this is where our cells start off they might get little bit bigger the cytoplasm gets little bit bigger but we've talked about before how important it is to keep that surface area to volume ratio high in order to do that we need to make sure the volume stays small but we increase the surface area so again the cell will grow it's done growing okay it'll come out and sometimes they say that it's in g0 and that's just going to be considered one of the cells doing its normal job when it's pumping out proteins and all that good stuff now let's say we're talking about one of the cells in your arm bone so if this is one of the cells in your arm bone it would be in g0 because you're fully grown doesn't need to divide anymore and it's fine however if you just if you happen to break your arm that sells going to now have to divide so then it reaches this our checkpoint which decides whether or not the cell is going to divide if your arm broke this all knows it needs to divide get certain signals certain growth factors so it's going to start the process of cell division or get ready to start the process that's when we enter the phase the phase is where our DNA is replicated this is really important aspect we drew that out on the board ok remember normally in your ass face we wouldn't really see the individual chromosomes it would actually be big tangled mess and these big tangled mess of chromosomes would all replicate and then once they replicate we also have our come over here are centrioles you normally have one pair during phase or Central's replicate after we leave phase we enter into to the g2 phase is where the cell is going to make its final preparations to divide all of that this whole entire aspect here is what we call interface so interface of three phases g1 and g2 most cells are going to be in g1 if they're fully grown if they're not dividing they stay in g1 sometimes refer to it as g2 for whatever reason if the cell needs to divide that's when it's going to move into phase again there's very important checkpoint right here that controls that phase DNA replicates DNA synthesis asked for DNA synthesis DNA replicates sentra centrioles replicate and then we move into g2 where the cells just preparing to divide that'll take us to the last the second stage of the cell cycle and we call it and it's an phase consists of two parts REM phase consists of what we call mitosis which is division of the nucleus we see that over here so in mitosis division the nucleus and we're going to end up actually with one cell that's going to have two nuclei in it and we know we can't have that so eventually we're going to have to get into second part of in phase which is what we call cytokinesis remember saito mean cell kinesis has to do with movement we're actually going to be splitting the cytoplasm so this would be the process of cytokinesis this is what you would see the cytoplasm the nuclei had already divided and now the cytoplasm divides until eventually we end up with these two identical sets so that's brief overview of our cell cycle again we have two major phases interface and then is interface is divided into three stages g1 and g2 we only get to the phase and g2 if the cell is going to divide once the cell leaves g1 once it goes past this checkpoint it's committed that means it is going to divide okay the only way it will stop dividing is if something happens along its journey to get into phase DNA doesn't replicate like it's supposed to the Central's don't replicate anything like that is the cell will self-destruct and we talked about what that was apoptosis which is when the cells self-destructs and again this is good diagram this is what you did in your coloring we're looking at the entire cell cycle so this over here is what we call the cell cycle for the life cycle of the cell and we have inter phase going all the way around we know g1 it's doing its job and then once it gets certain signal right here is where we're going to have our checkpoint and it's really important for you guys to know that to understand that in order to proceed to the other parts of the cell cycle to continue on to phase it has to reach this checkpoint it has to get the right signals or right proteins to go on to the next stage once the cell goes on it is committed it will finish the cell cycle s-phase DNA replicates make sure you know that and then phase we prepare to divide and then we enter face and you can see phase is divided into two stages the first stage is what we call mitosis again division of the nucleus and then finally our cytoplasm splits and we end up with our two new daughter cells what is actually controlling all this ok we have internal and external factors that control the cell cycle which we're going to get to and just want to point out in this picture these are some of our internal factors that the cell uses to control how it goes from g1 g2 and we call them cyclones and cyclin dependent key neighs of this and all you really need to know about that is there really important proteins and this one should give it away it's key neighs SE ase means enzyme so cdk is cyclin-dependent kinase and then we have our cycling's which is just another protein which is going to be our substrate so if this is our cyclin this is our cyclin this would be our cyclin dependent kinase and so this guy would end up attaching over here once they're attached the cell will proceed into the next stage the most important thing to remember about interface is that there's many checkpoints found throughout an interfacer checkpoint in g1 there's checkpoint and ash there's checkpoint indeed 2g to the importance of these checkpoints is to make sure everything in the cell is ready to go make sure that the DNA is replicated properly that there aren't any mistakes if there are mistakes then the cell will not go past that checkpoint and it will go through apoptosis many cells from most of their life in g1 because they're non-dividing cells so those would be such as our muscle cells or our brain cells like mentioned before we have different types of regulators for ourselves we talked about those internal regulators which were our cyclin-dependent kinases and our cyclones and those again are just proteins fancy names for some important proteins in the cells like cell cycle and we have couple of them we have many different types and you can see up here this is one cdk this is another one and they're going to play it very important roles in controlling how the cell moves through this process we refer to them as internal regulators of the cell cycle they control everything from the inside so just keep that in mind you'll never really be asked question as to what is cyclin-dependent kinase but it might ask you how does this cell regulate the cell cycle so you need to be able to differentiate between those internal regulators and then the next thing that we'll talk about which is what we call external regulators external regulators think outside the cell that are going to control the cell cycle for example when you break bone at the two ends of the bone that are broken the cells will begin releasing proteins that will signal to the other cells across from it to start dividing those would be external regulators sort of factors outside the cell that tells other cells are rounded to start dividing growth factors is very good example of how external regulators get cells to go through cell division one import another important external inhibiting an external regulator is what we call contact inhibition and what contact inhibition has to deal with is that when cells are dividing once they and we can look over here and imagine these are the two ends of your broken bone they release external signals external proteins to tell the cells across from it to start dividing once they come in contact with each other and there's no longer need to divide okay contact inhibition will occur and the cells sorry the cells will no longer divide however if those cells for whatever reason do not have their external signals working properly such as those membrane proteins extrinsic or intrinsic transmembrane proteins if those proteins aren't functioning properly and they don't recognize signal from contact inhibition to stop and they will continue growing out of control and that's when we get what we call cancer which we'll get into later all right so now we're going to dive into the second major part of the cells life cycle we already talked about interface now we're going to look at phase and this is where the cell is actively dividing and it consists of two different stages mitosis followed by cytokinesis again mitosis is division of the nucleus and cytokinesis is division of the cytoplasm and finally when cytokinesis is over that's what we have our two new cells easy way to remember the stages of mitosis is p.m. little acronym to remember the four stages in the proper order and we'll go over what goes on in each of these stages so let's go ahead and look at profiles when we look at prophase okay the first thing that you need to know is that those DNA molecules that were all spread out as chromatin they replicate it but there's still big tangled mess suddenly become condensed and visible and that's when we can actually see them so chromatin becomes chromosomes the nuclear envelope will start to break down that's represented over here by these broken down orange lines the nucleolus will actually completely disappear so we won't see that anymore and then we're going to see our centrioles start to move to opposite ends of the what would say would be the nucleus if we're still there but also opposite ends of the cell and when these central's are moving to opposite ends we call the region where we find the centrioles centrosome and that's pretty important to know because we can use either word we know that plant cells don't have central centrioles so they have what we call the centrosome and this is an area where we start having microtubules coming together to make what we call spindle apparatus and all that is is an area that's going to send out microtubules to attach to the centromeres which will see happening later on if we come down here this is natural micrograph and you guys will be looking at some onion root tip cells and be trying to identify different stages of mitosis all these cells here we'll go ahead and get pen so we can actually see what's going on little bit so all these cells over here if we're we're looking here these are the nuclei and these nuclei the ones that I'm circling right now are all in interface and the reason we can tell they're an interface is because if you look in the nucleus see how it's very very grainy that's all of your big tangled mess of DNA as chromatin now when we come over here we can actually see the nuclear membrane starting to break down and then inside you'll notice that's not as much of mess as it was over here we can actually start to kind of make out some chromosomes coming together okay condensing we can make it out little bit so this would be early prophase this is very beginning now at the very very end of prophase we all no longer see any nuclear membrane or envelope that's completely gone will also notice that all these chromosomes or all that chromatin is now visible and so we call we now can officially call them chromosomes because we can actually see the individual chromosomes they're not organized in any particular way but it's very different than these cells here here here here okay and even our early prophase so make sure you know how to identify it early prophase late prophase and the major events that happen now want you to pay special attention to this okay what we have at the end of prophase because when we get to teal face it's the exact opposite so keep this in mind you can always flash back to this slide if you want to review i'll have it again on the Tila face like right so after we finish up with prophase and we have those nice visible chromosomes we're going to enter into what we call metaphase and like told you before remember metaphase em middle that's an easy way to remember it metaphase is where our sister chromatids are all going our sister chromatids are still attached to each other are all going to line up in the middle of the cell and that's again why we get the name metaphase and as they line up in the middle what we're going to see start to happen is these microtubules from these centrosomes where central's were are going to start to extend and these are proteins so again another really important job of proteins is to make up these microtubules that are going to attach to each centromere and that's essentially what happens in benefits now as far as how long metaphase takes varies depending on organism sometimes it can take ten minutes 20 minutes 30 minutes it's different prophase also takes prophase usually along as fifty to sixty percent of mitosis is spent in prophase will usually be seen lot of cells in prophase to face not as long but still good amount of time spent in metaphase so the third stage of mitosis is what we call anaphase and told you just easy way to remember anaphase for anaphase for part or way this is where the sister chromatids get separated and they get pulled apart so once they lined up in the middle and those spindles attach they're going to go ahead and yank them apart and this is really important because this is going to happen very quickly okay this stage happens very quickly so when we're looking at our slides trying to find cells going through anaphase it's going to be little bit more difficult because they don't spend as much time in this stage of mitosis so these sister chromatids are pulled two opposite poor opposite poles and then they're going that as soon as this is done we're going to get into our next next phase which is love and our last stage of mitosis but not the end of cell division the last stage of mitosis is what we call Tila phase and told you guys this is the exact opposite of prophase so everything that would happen in prophase okay we do the opposite over here in telophase we're going to see that the nuclear the nuclear membrane is actually going to start to reform so when we look up top in the top right-hand corner if we look at our nuclear membrane you can see that it's starting to reform over here around each set of chromatids on the opposite poles we're also going to start to see the nucleolus repair reappear because it wasn't there the whole time mitosis was going on it's going to reappear we're also going to see the chromosomes that were so visible before start to spread out and tangle themselves back up into our chromatin and then finally we're going to see our spindle apparatus is going to break apart our Central's are still there but those spindles and microtubules are no longer there now the same exact time low phase is happening cytokinesis is also occurring so even though all this is going on here in the new clue nuclear membranes reforming the cytoplasm is actually getting ready to split up and so they happen at the same time we'll be able to recognize this fairly quickly so cytokinesis is division of the cytoplasm and when we look at cytokinesis it's going to different animal cells and plant cells when animal cells cytoplasm divided we know that animal cells do not have cell wall so therefore we don't have to make you cell wall all that has to happen is our cytoplasm needs to split and that's exactly what occurs what we get as cytoplasm begins to pinch off is something we call cleavage furrow and i'm just going to backtrack really quick just so you can see that because this picture demonstrates the cleavage for cleavage furrow fairly well this little area where it's pinching off let's go ahead and get pen going this little area where it's pinching off right here this is what we would call our cleavage firm so you want to know that term that's an easy way to differentiate between cytokinesis cytokinesis in an animal cell in plant cell animal cells have cleavage furrow we don't have cell membrane ok so now looking at plant cells when we want to see how they go through cytokinesis they're going to have to begin to form their cell wall quick review what's the cell wall made out of ok the cell walls are made of cellulose really important for you guys to know that in order for the cell wall to be made we have these two new cells are going to begin secreting some of those carbohydrates and polysaccharides and they make something we call cell plate eventually that cell plate will form around each of these cells forming their cell wall so that's big big thing differentiating cytokinesis in animal cells and cytokinesis in plant cells so make sure you know to look for that cell plate when we're trying to find plant cell going through cytokinesis in tea loaf age to your face so that this basically sums it up this picture here now you should be able to identify each stage of mitosis going on in this picture it's pretty easy because it's kind of an order for you these are plant cells that we're observing here you can see in the first couple number 12 are going to be cells in interface so they're going to be in g1 g2 DNA replicated and you can actually kind of see the DNA replicating in these cells here you can see another picture number one okay not as dense and if we come over here we actually see that that tangled mess is little bit denser so this means this would likely be in g2 this was probably in g1 so then we enter into prophase so these here these three three four and five these would all be cells in prophase and you should be able to identify which ones are in early prophase and then this is late prophase you can really see those individual chromosomes then we come down here and this is really good example of metaphase okay both of them this is where our sister chromatids all aligned in the middle what we really don't see is that these spindle fibers were actually coming over and attaching and they're coming over from the centrosome region from where the centrioles were so they've attached the place where they attach it's called the centromere so they attach the centromeres of each sister chromatid that's what we have going on over here and then we're going to enter into and again this is metaphase don't forget then we're going to enter into anaphase not the number eight in phase they're being pulled apart so those those spindles are actually shortening which is really important that proteins are able to shorten themselves move all of that they're actually being pulled in opposite directions and then we enter into our tilo phase now remember telophase and cytokinesis happen at the same time and it's little bit harder to see what's going on here but what we're going to start to see happening is our nuclear membrane is going to reform nucleolus reappears you can go ahead and draw that out on your own and as that's happening what we'll end up seeing is cell plate begin to form until eventually we have our two new cells and you can see two new cells we no longer see our sister chromatids or we no longer even see our condensed chromosomes now it's big tangled mess of DNA and another big tangled mess of DNA and now we're back to looking like this cell up here our original parent cell with the big tangled mess of the unit and that about does it for our lesson on the cell cycle and mitosis know this was lot of information why didn't go ahead and practice identifying those stages of the cell cycle in the picture on the screen and then we'll have quick review in class when see you next week