all right so this online lecture is mostly about chromosome shape and we're going to spend a lot of time on mitosis which is a process in which ourselves are actually going to replicate in particular the nucleus of how we split our nucleus in half in the process that goes along with that so as we dive into the structure of chromosomes we've kind of touched on that a little bit with the first or my lecture but I want to talk about a little bit more in depth when we look at our chromosome we know that a chromosome is essentially comprised of this double-stranded RNA molecule so let me just go ahead and set up the pointer all right it's comprised of this single linear double-stranded molecule so we know our DNA is going to be comprised of a strand and those strands are going to come together to form a double helix and that's what this first line is essentially talking about so when we talk about the DNA paired with the proteins that I'm going to discuss so DNA plus proteins that term is called chromatin so for instance this DNA picture with the cromoz with the protein present is called chromatin the protein in particular that is present in this chromatin so DNA plus the protein the protein has a specific name in that name is called a histone so from the images here these little circular proteins we call that histones so anytime DNA wraps around a protein the specific name of that protein is called a histone well we're talking about one single unit of DNA and histones together or DNA and proteins together that is called a nucleosome so in the image here of course the red line is your DNA this pink protein is your histone but one unit of them together is called a nucleosome and when our nucleosomes are organized they're organized in the zigzag shape so if you see here you can see it really well it kind of goes up down up down up down this is going to be called a 30 nanometer fiber shape I know this is a lot but just make sure you get some flip cards with this type of stuff but a 30 nanometer fiber shape so when you see DNA that's wrapped around histones in this zig zag orientation that particular shape is 30 nanometer fiber shapes so when the 30 nanometer fiber shapes get together to start to get closer they're going to begin to form these loops so you're going to have the 30 nanometer fiber shapes as it says here and then you're going to have these pieces of DNA that just loop out and form a loop that loop is called a radical loop domain so this is just space between our 30 nanometer fibers and other third and an amino fibers it's going to be a loop called a radical loop domain once we look at the level of compaction within the nucleus we're going to realize that some areas of the nucleus are going to be highly compacted meaning taking all the DNA and squish it together that's going to be heterochromatin so the dark spaces are areas in which DNA is really really tightly wrapped around each other but areas in which DNA is not tightly wrapped around each other that is called euchromatin so in this image here the white areas are euchromatin the dark areas are heterochromatin so putting together everything we've seen so far of course our DNA double helix is here in this spiral format once we begin to wrap it around the protein in which we call a histone now that is called a nucleosome those nucleosomes form these zigzag patterns called 30 nanometer fibers and eventually big loops of those 30 nanometer fibers form these radical loop domains and then eventually they all compress and compile to form a chromosome that we know and see so this is just a detailed account of how we get to this chromosome I think in the first lecture we kind of discussed this part and we skipped over everything here in the middle but this part is really critical as well all right so now I'm going to cover the cell cycle and the cell cycle is oh it has a lot of terminology so we're going to go through it slowly and I do not mind covering this briefly in class but make sure if there's questions you give me some specific questions so that we don't repeat the lecture in class and also had you you know do the lecture online so when we talk about the cell cycle this is just a series of step by step events that are going to lead to cell division and more importantly nuclear division so first we want to again revisit our chromosome when we study chromosomes and how they look in how many we have we call that field cytogenetics so genetics is our genes and the instructions to make proteins and the Saito is a cell right so understanding the genes of the cell form cytogenetics when we're talking about karyotypes a karyotype is going to show all of the chromosomes that are found within a organism and it's going to tell us stuff about the size the gender of the organism as well as the number of chromosomes we have in each each particular chromosome position so this is an example of a karyotype this is actually a human karyotype because we can see there are 23 pairs of chromosomes so you see each chromosome is kind of in these sets of similar chromosomes with it so it's a pair although sometimes they have a curve here there but we're able to see after you the 22 you see this final set here this final set here is actually what we call a sex chromosome so it determines the gender of what you are observing and if you did not know the X Y chromosome is representative of a male as opposed to xx which is representative of a female so this would be the the the carrier type of a normal male because there's no chromosome abnormalities here and we'll talk about some other things later some things like Down syndrome or Klinefelter syndrome in which you can look at this and you'll be able to see there's going to be a certain number of additional chromosomes or certain missing chromosomes along the way alright so again what you see here is humans again have 23 pairs of chromosomes which means we have 46 the first 22 pairs of chromosomes we called autosomes so chromosomes one all the way down to 22 are chromosomes that are going to affect just general things that you need to make a human so these are going to be 22 pairs but then the final pair is called the sex chromosome so again XX is female XY is male in this picture is just showing just that one Y chromosome showing that you know we have the Y chromosome present so whenever they're doing gender tests they can actually look and see let's say the mother who is XX if they look in her bloodstream or if they look at genetics and they see Y chromosomes present that must mean there's a male child if they don't see any Y chromosome friends that can also mean that it's just a female some of those things so when we're talking about sets of chromosomes we usually use these two terms diploid or haploid so for some for a set of chromosomes to be diploid we also call this to in they come in as a one individual chromosome so you basically have two chromosomes here so humans have 23 pairs of chromosomes so humans are known as being diploid because all their chromosomes come in a pair right because it's two in so they're diploid or two in humans are diploid however if you only have one set of each chromosome so for instance if you looked at this picture and it wasn't two chromosomes in position six it was just one in six one and seven one and eight one and nine blah blah blah that's going to be haploid or in so that just means you have one set if something is haploid we can also call it a gamete and gametes only have one member one component of each pair of the 23 chromosomes you see gametes in your reproductive cells such as your sperm cells for our guy and our egg cells for our girls that's because if your mating it'll say you're a female and your mating with a male you want to give one set of your chromosomes and they can give one set of their chromosomes to make a complete organism if you're giving two sets and they're giving two sets then now you have four and four is not what we need we need two so only in your sex cells or your gametes your egg and sperm cells do you have one one member of each pair everything else in your body is going to be diploid or have two so again this is just reinforcing that idea haploid cells are going to just have one you see one pink one purple one yellow versus diploid have two there's also other versions called triploid and tetraploid but this is not very common in the animal kingdom as much as it is in other organisms alright so when we're talking about diploid or 2n species if they're part of a pair so let's say number four is these two chromosomes and number four we call them homologs of each other so they are known as being homologous chromosomes so when we're looking at our homologous chromosomes I'm actually going to jump forward to this picture and then I'll go back is an allele is a certain space on a chromosome so we're in this particular base pair of homologous chromosomes you can see that there is a an allele that says whatever gene this is is going to be blue and the other pair says whatever gene this is is going to be purple so an allele is a certain position on a chromosome if we're talking about whether you have a widow's peak or not you're going to get one gene from mom one gene from dad let's say we're at the bottom with this red one this gene says have a widow's peak this gene says have a widow's peak you will have one as prepared to these other ones in which this says have a widow's peak this one says do not you're gonna have somewhere in between and we'll talk about that so again an allele is the same place on a homologue that carries that gene so we're basically just comparing and contrasting between chromosome one and the pair for chromosome one that's what an allele is kind of disgusting and again highlighting that there so as we go into mitosis um I want to introduce again the cell cycle so all of your cells in your body they start off very small of course and then they're going to grow and as they grow they're going to either do one of two things they're either going to stop growing completely or they're going to divide it's like a balloon so if you either blow up a balloon you can realize if you keep blowing it up it's going to pop so you can stop it or you can pick up another balloon and start blowing that one up um so all cells are going to do that so the cell cycle is the set of stages so you see right here we're going to cover it's the set of stages that a cell has to go through to be able to go from not dividing to dividing so going from growing growing growing growing growing to dividing and then continuing to grow grow grow grow grow and divide so these are the specific stages that the cell has to go through so the first stage is called G 1 so G 1 is called it's just the first stage it's known as the gap one stage let me just clarify make sure I don't have it oh I do have it expanded a little bit later so I'll quickly go through this part so do you one again is just the first gap phase which I'll tell you about what happens there S phase is s for synthesis synthesis means make so we're gonna make a lot of stuff here g2 is the second gap phase and then finally the in phase is mitosis in which we undergo mitosis and cytokinesis so when you're looking at the cell cycle although there are different phases within it they can be broken down into two main phases which is interphase so that's the blue line that goes around the this image here interphase is comprised of g1 s and g2 and then the final phase is M phase which is composed of mitosis and cytokinesis so most of your cells in your body are in interphase that means your cell is not dividing it's just doing its cellular thing so this is an image of what a looks like the blue is the genetic material and then you know this is a cartoon picture of it there so most of your cells in your body are just you know doing their cellular activities nothing too major and then there are some cells in a special page called zg0 which cannot divide so an example of that would be your brain cells or your neurons also your muscle cells so once you get a certain number of brain cells you cannot get anymore so what you're born with is what you have that's why I unfortunately sometimes people go through different traumatic brain injuries or things like alcoholism or different drugs and you can't rebuild those neurons also that happens with muscle cells as well so if a cell does not divide if it never divide it's always in a g0 phase g1 think of the G is growth because normally what happens in g1 is your cells just growing is going through normal metabolism it is essentially the stage that happens after yourself just divided so your cell is essentially just growing and doing normal cellular behavior the S phase is where DNA replicates so on all online online lecture we haven't fully covered DNA replication but when we do if you ever got asked a question which stage of cell cycle does DNA replicate it is the S phase or the synthesis phase this is also where you make those hiss teen protein proteins as well and finally the g2 phase instead of growing we're starting to create more proteins that we need for division because remember if you're talking about your cell your cell is growing growing growing growing in g1 when it gets to S phase it duplicates its DNA so your cell can't just stop here because it has two sets of instructions on what to do so it has to go to the next phase which is d2 so that I can start making more proteins to eventually prepare for mitosis if it ends up here this can cause a lot of diseases or a lot of cellular problems or the cell might naturally just die off so that it can you know it won't be dysfunctional so the in phase again its consists of mitosis and cytokinesis so mitosis is the nuclei division so remember our DNA is going to be in our nucleus and we have to go through a very very particular process of taking our nucleus in dividing it in half we want to make sure that we are dividing our instructions very carefully so that we don't start making cells that have the wrong instructions and we'll do the wrong things that leads to diseases that can lead to cancer that can lead to some really bad things so we want to be very careful with that process and that whole process is called mitosis that's where you duplicate your nucleus or divide your nucleus to get two identical nuclei it has five stages we'll go through each one prophase prometaphase metaphase anaphase and telophase now sometimes you do not see prometaphase it just goes from pro to meta but in the book it covers it so I'm going to cover it for you and finally cytokinesis is where you've already split apart your nucleus so now your cell has two nucleus and now you just split apart the cytoplasm which is all the cytosol and/or other organelles inside the cells that you have to separate cells alright so the first stage is prophase so prophase begins when chromosomes become visible so the reason that this is important is if you remember a few pages back normally your cells when they're in interphase they are not in a chromosome structure they're just loose and the cells are not tightly compacted but whenever we switch over to prophase your chromosomes start to become visible so it goes from chromatin which is just more stringy to chromosomes which are more organized and again for them to become visible it'd be it occurs through this compaction of the chromosomes another thing about the chromosomes if you see here in this little blue dot in the little image here at the bottom is attached to east each centromere which remember is the middle part of the chromosome is this think of it like a handle is a little handle called a kinetochore so attached to the middle part of the chromosome is a little handle called kinetochore and microtubules which you may remember from cytoskeleton is going to be able to attach to that so eventually we're going to do a lot of pulling and think of your chromosome having a handle so that the cytoskeleton can grab the chromosome and pull it wherever it needs to go so the centromere is in the middle of the chromosome the kinetochore is the handle and the microtubules are the strings that will eventually attach and then the mitotic spindle occurs which is essentially another another term for the strings that we're going to use to be able to pull apart our chromosomes the final thing that begins to happen in prophase is our nuclear envelope begins to dissolve so if you remember our nucleus is inside of an envelope where nothing gets inside and it but it begins to dissolve because we have to reach our chromosomes remember our cytoskeleton and everything is on the outside of our nucleus so we have to first dissolve the nuclear membrane so that it can reach inside and grab the chromosomes again the mitotic spindle is the string that's going to be able to connect but you can see it a little bit closer here the centromere is the middle of the chromosome the kinetic are the blue pieces that are the handles and then your microtubules will attach to each side so in prometaphase it's basically extending what prophase is so in prophase we talked about how the nuclear envelope starts to break down and prometaphase it breaks down completely we talked about the mitotic spindle forming in prometaphase it completely forms and again our kinetic are going to be fully attached to our chromosomes and our centromere in particular and then finally the chromosomes begin to move towards the middle of the plate now they are not in the middle of the cell but they're starting to move towards the middle of the cell so if we go back to our other picture all we see here is that they're starting to condense a little bit more but as we go deeper into prometaphase they're starting to align in the middle of the cell so I believe it the way this picture is is kind of vertical alright so metaphase meta means middle so anything is meta meta to means middle so this is where all the cells chromosomes align or line up in the middle of the cell so this big blue area I'm sorry this big red area is the cell itself and the blue area is the DNA it's going to line up in the middle so each chromatid each chromosome is completely in a chromosome format excuse me and the main thing that happens in metaphase is it lines up in the middle now remember although it's lined up in the middle like you can see here in this picture it still has a kinetochore which is attached to the microtubule or the string so keep that part of mine so metaphase is where it lines up in the middle and it is begins to be attached to opposite top sides of the cell anaphase think of anna is separate anna is where the sister chromatids or the pair remember it's an X this is where your X begins to separate so imagine if you look back here you have an X I'm looking at the magenta one at the top if you look here in this image they separate them and pulled apart so this kinetochore each side the microtubule each side pulls it apart so that they go to opposite sides remember our end goal is to make two different cells so if we start to get some genetic material on the left and some to the right this is going to be much easier for us to split the cell apart down the line so in anaphase they're going to separate and move towards opposite sides it ends when the chromosomes have reached the pole so when they have reached their side of the pole is what it's going to end and finally telophase is when the chromosome starts to return to anaphase like tradition Sotelo usually means end so at the telophase part we're basically done so we're ending everything that we have the chromosomes have moved to their sides and we're going to start to begin to separate the cell so the difference between anaphase and telophase is telophase everything's starting to dissolve you're starting to form you're starting to have your chromosomes D condense and start to uncoil and get back into a chromatin format and then you also start to form a new nuclear envelope so you see in the picture here they're starting although you can't really see that chromosomes they're there they're going to start to become more loose like the chromatin format and they're going to also begin to get the nuclear envelope around them as well so the final step telekinesis I'm sorry telophase and cytokinesis usually go hand in hand it kind of happen at the same time but as your nucleus is starting to get a nuclear envelope and and get back and take interphase type conditions cytokinesis is what happens where we finally divide the cytoplasm remember everything we did before was the nucleus now we're dividing the cytoplasm evenly to make sure that 50% goes into one side 50% goes into the next side so like I said it usually happens at the end of telophase and kind of overlaps the mitosis before we get all the way into interphase and what happens is think of like a drawstring bag right I think of an open drawstring bag anything with a drawstring if you pull both sides that hole is going to start to get smaller and it basically will start to form to set a plane so you see imagine this was a big open area and this was a drawstring you're going to basically kind of snip off or cut off the cell at this point and this little tip that forms here is called a cleavage furrow so just like we know the word cleavage means split from what we did was say the respiration a cleavage furrow is this little split is this little dip that occurs here that's going to be where we can separate and deep in the cytoplasm so all right so cytokinesis implant is much more simple instead of having a cleavage furrow what we see is little vesicles or little bubbles form in the middle of the plant cells remember the plant cell has a cell wall so it undergoes everything normally as far as anaphase tell anaphase telophase metaphase all that stuff but what you see is little bubbles form in the middle and then the little bubbles started into medium bubbles when they merge and then eventually they turn into one large big bubble and that's going to be your your cell plate that forms so that's how you keep that a nice square shape for plants so much easier glance so again this is going to be an image depicting what we just covered so again our prophase has both prophase here and prometaphase you can see in prophase the nuclear envelope starts to dissolve your chromosomes start to become condensed you start to see microtubules forming and prometaphase nuclear envelope is completely gone your chromosomes are your chromosomes are completely attached to their microtubules and they're starting to come towards the middle metaphase are completely in the middle completely attached anaphase they're separated and telophase they begin to get back to interphase type conditions and have a cleavage furrow forming in the middle and again this is just another image putting all that together as well prophase prometaphase metaphase anaphase telophase this is an image from your book so I wanted to again highlight what the book has just cuz I think it's important for y'all to have a similar analogy and this is again showing all the different stages and all the different areas that were covered so far all right so when we talk about our daughter cells what do we end up with we end up with a daughter nucleus that has the exact number and the exact kind of chromosomes the parent cells had so it is the same and identical there's got to be something we talk about later that's going to be a different number and I and a different type of chromosome but anytime we do cellular division under mitosis it is going to be exactly the same number in exactly the same kind of chromosomes so this is again if you you stepped on some glass and you cut your foot you don't want your foot to start forming cells that are supposed to be in your arm they should be the same exact cells over there before and this is what happens in mitosis the organelles are also split easily so we won't cover that but they make sure there's an even split and remember our mitochondria and our chloroplasts and plants have their own DNA so they do their own thing so when we're talking about mitosis we're not covering mitochondria because they divide on their own own way also when we're talking about the cell cycle there are a few terms here a one is called cycling or cyclin dependent kinases so if you see this is an enzyme and these are enzyme proteins that control if and when your cycle moves forward now this is really important we're not going to go into this in depth but if you have any type of cell bio class or any upper level biology class you will and we won't cover them like we should but basically what happens here is your body will be able to stop the cell cycle when it needs to stop it or tell them to go when it needs to tell it to go so for instance if you're supposed to have 46 chromosomes and during your duplication stage so at the end of the synthesis stage S phase if you realize you have 46 times - what is it 90 92 something like that let's say is 92 right if you had 95 then they'll realize that there was something wrong and this will stop the cycle from moving forward you don't want to move forward with 95 chromosomes because you're gonna have an uneven number of chromosomes you want to have the right number of chromosomes so this is going to help regulate if and when the cycle moves forward so this is called a cyclin or a cyclin dependent kinase so this will be a good question as part of one of my bigger questions what would you do if if you realize your cycle you had 100 chromosomes and you're supposed to have 85 what type of protein will probably stop the cycle from moving for it it would be a cyclin and finally there are other key molecules that can also play a role besides cycling's one is hormones so plant hormones can promote certain types of mitosis as well as steroids so there's tons of steroids if you think of [Music] I'm thinking of what I can't recall the major one that people usually use quarter quarter steroids or different steroids you can use for your skin different topical agents that has been used to help with wound healing and help to decrease scarring in different tissues so some steroids can stimulate growth and mitosis also there are different type of protein growth factors that can stimulate cell growth but there are some drugs especially a lot of our cancer drugs that can stop the cell cycle a certain part so as I mentioned before one of the the tricks that cancer uses is that even though it begins to duplicate with the wrong number of chromosomes or something is wrong in the cycle it can interfere or bypass so cycling so that it keeps growing so cancer is typically uncontrollable cell growth and that's why unfortunately it's associated with tumors and things like that so a lot of times cancer takes over your cell cycle system and it just grows and grows and grows but a lot of the drugs we have on the market work by targeting cancer cells and putting a stop to the uncontrollable growth by inserting a cycling or entering something that will limit that cell's ability to duplicate and finally so we covered how this works in animals and plants and bacteria they divide by a very simple process called binary fission so if you look at fission there's two essence put a little line in the middle that's how you know it separation or you're breaking it apart during this the only thing that happens is in DNA and bacteria the DNA will duplicate or replicate then you begin to form a cell wall that's going to kind of be like that cleavage furrow that just splits it in half and you have two cells so the only thing that happens in prokaryotes or bacteria is the DNA divides it begins to constrict or form that drawstring cleavage furrow that we talked about before and the next thing you know you have two bacteria that's why bacteria can replicate really quickly so something like e.coli rep replace in about 20 minutes which is why if you get food poisoning you feel sick you could feel sick later that day because it can duplicate very quickly again this is just showing that in a more compact this is your cell that duplicated it's going to have a separation more specifically called septum think of like a nose ring a lot of people get septum piercing which is that middle part of your nose it's going to form a separation and then the cells are going to be able to duplicate alright so that's the end of our online lecture it was a little bit longer than anticipated but I hope that you found some value in it and this is going to serve as what you're covering in class for the week that I'll be out have a good one