Full transcript
0:06all right ninja nerds in this video we
0:09are gonna talk about the cell cycle the
0:10cell cycle is so important why because
0:14the cell cycle which we're gonna talk
0:16about interphase and mitosis is the
0:18series of phases and steps that a cell
0:21goes through to replicate itself so
0:24we're gonna turn one cell into two cells
0:27and this is an important important
0:29process not only is the cell cycle it
0:32just important for being able to
0:33replicate cells but it's also important
0:36to be able to control cell growth we'll
0:39talk in another video about the
0:41regulation of the cell cycle will talk
0:43about proto-oncogenes we'll talk about
0:45tumor suppressor genes and we'll talk
0:47about DNA repair enzymes and genes okay
0:50but in this video we're gonna discuss
0:52the cell cycle so we're gonna go through
0:53the various stages of interphase then
0:55we're gonna go through mitosis and then
0:57another thing for you guys is during the
0:59mitosis part I'm gonna show you what's
1:02going on in the board
1:03but just to get a different view we're
1:04gonna take models that are gonna show
1:07you guys a little bit more of what it
1:09would look like in the cell during
1:10prophase metaphase anaphase telophase
1:12okay so let's go ahead and get started
1:14on the cell cycle before we do that how
1:17would you describe a cell what is a cell
1:19a cell is basically it's the basic unit
1:22of all living things and the cell is
1:25classified by technically having three
1:27different things so this is important to
1:29remember a cell is classified by having
1:30three different things what are these
1:32three things generally since we're
1:35talking about eukaryotic cells because
1:36there's eukaryotic and prokaryotic cells
1:38right we're gonna talk about eukaryotic
1:39and specifically human cells they have
1:42to have what's called a cell membrane so
1:46they have to have a cell membrane and
1:48remember that the cell membrane is a
1:50phospholipid bilayer right that is
1:52actually surrounding the entire
1:54structure it also has to have a nucleus
1:58where it houses its genetic material
2:00okay in the form of chromatin which is
2:02the DNA wrapped around different types
2:04of histone proteins and the last thing
2:08is you wanted to have cytoplasm
2:11this is the three basic units that are
2:13needed for an actual cell so a cell is
2:15made up of three different things a cell
2:16membrane a nucleus and a cytoplasm what
2:18we were going to do is we want to take
2:19this and make another one an identical
2:22cell in the nucleus we have a structure
2:25though we just we briefly described it
2:27here and we said its DNA all right so
2:29we're gonna take the DNA during this
2:32process of the cell cycle we want to
2:34duplicate the DNA we want to replicate
2:36it we want to synthesize a new
2:39double-stranded DNA and we're gonna talk
2:41about that in this video so let's go
2:43ahead and get started here so the first
2:44part of the cell cycle let's say we take
2:47a normal cell alright a normal cell that
2:50cell is gonna get ready to go into the
2:52cell cycle what's the first point that
2:55it'll go into in the cell cycle the
2:58first phase is called the g1 phase so
3:03it's called g1 phase sometimes you might
3:06even hear it referred to as gap one it's
3:11the gap one phase
3:12so it's either g1 or gap one phase now
3:16in this phase what is the cell going to
3:19be doing so now let's pretend we take a
3:23cell right so here we're gonna have a
3:25cell in the cells entering into this
3:28phase here alright it's entered into the
3:30g1 phase now cell we said has a cell
3:32membrane right it has a nucleus which
3:34houses genetic material and around that
3:35has the cytoplasm well the first thing
3:37we're going to want to do is is we have
3:40to be able to get this cell ready so it
3:42can replicate
3:43right we want to take one cell and turn
3:46this one cell into two cells that's the
3:49whole goal and we want them to be
3:51identical not only just identical but
3:54how is the same amount of genetic
3:55material
3:56so in general we know that this is a
3:58diploid you know in all of our cells we
4:00have our chromosomes right and there's a
4:03total of 46 chromosomes 23 of them are
4:06maternal at 23 over the paternal we want
4:09to be able to pass the chromosomes down
4:12so we have to duplicate it in order to
4:14duplicate it we have to have both of
4:16these cells also be diploid so we have
4:19refer to to in as diploid meaning that
4:21has a total
4:2346 chromosomes so two men is
4:25representing 46 chromosomes the end is n
4:28is basically representing the number of
4:30chromosomes and again we have 23
4:32maternal and 23 paternal so if we take
4:35that 23 times 2 is going to give us 46
4:37total chromosomes and then what we want
4:40to do is we want to replicate this into
4:41two identical cells with the same number
4:45of genetic material same number of
4:47chromosomes that is mitosis all right
4:49but in order for us to go into mitosis
4:51we have to have this first part here
4:53called interphase and we'll talk about
4:55this all right so now first thing for
4:57the gap one phase if we need to be able
4:58to replicate these cells what should I
5:01do
5:01well you know another thing that these
5:03cells have our eukaryotic cells have is
5:05they have different organelles like
5:07ribosomes they might have mitochondria
5:10you know they can have different types
5:12of organelles so the first thing we
5:14should do is we should increase the
5:15number of organelles let's make more
5:17organelles
5:18so the first thing here that we're going
5:20to want to do here is make more
5:25organelles okay cool
5:28what else they're gonna want to do well
5:30you know inside we said inside of this
5:33actual nucleus what do you have you have
5:35your genetic material your DNA well you
5:38know there's a process we'll talk about
5:40it it's called DNA replication in order
5:43for DNA replication to occur we need to
5:45have certain types of enzymes certain
5:47types of proteins right and an order for
5:50an even transcription factor so if
5:52that's the case then what do we need to
5:54start doing we need to start preparing
5:55the cell by making tons and tons of
5:58different types of enzymes so we need to
6:01start synthesizing proteins and enzymes
6:12now because we're gonna start making a
6:15lot of protein and enzymes to help to
6:17aid in this actual DNA replication
6:18process we have to say one more thing
6:21sometimes ourselves most of our cells
6:24hey this is another important point you
6:25know most of our cells usually exist in
6:28the g1 phase most of the cells stay in
6:31the g1 phase so out of the cell cycle if
6:34you if you were to ask if you were asked
6:36which out of the whole cell cycle which
6:38phase is this cell most likely in most
6:41of the time it's in the g1 phase because
6:43it's variable for certain types of cells
6:45what do I mean for certain types of
6:47cells they might only be eight hours
6:49that existed in this phase other cells
6:51it might be years you know there's
6:54different types of cells we should
6:55actually talk about that let's come over
6:57here for a second will deviate for a
6:58second but we'll come back there's three
7:00different types of cells that I want to
7:02talk about one are called labile cells
7:07or another LOI I like to think of them
7:10as proliferative cells I'd like to think
7:13about them as proliferative cells so
7:16what are lay bio cells are proliferating
7:18cells think about it simply out of your
7:21whole body where your cells constantly
7:24proliferating they're constantly going
7:26through the cell cycle all of the time
7:28right here we're constantly shedding
7:30skin cells so all the stratified
7:32squamous epithelial tissue on your
7:34epidermis and where else in the GI tract
7:37in the urethra the vagina many different
7:40places that's constantly undergoing
7:42replication so for these lab ourselves
7:44what can I say we could say the
7:47epithelium of skin
7:52where else the GI tract and maybe even
7:58the urinary tract so even the urinary
8:01tract okay in other places this is the
8:07coolest one I like this one if you think
8:11about it we have to constantly be making
8:13red blood cells and white blood cells
8:15and platelets all the time so because of
8:18that you have to have some type of stem
8:20cell that's constantly replicating and
8:22producing more of these blood cells what
8:24is that cell called it's called a
8:25hematopoietic stem cell so you know our
8:28hematopoietic stem cells that are
8:29located within your red bone marrow
8:31they're also lab off cells so what are
8:34they called they're called your Hamato
8:37poetic stem cells that are in the red
8:42bone marrow the red bone marrow these
8:48two types these basic types of cells
8:51these labile proliferative cells they're
8:53constantly going through the cell cycle
8:54now there's some cells that they don't
8:58want to go through the cell cycle all
9:00the time they're kind of stable of just
9:02resting staying in a kind of like I just
9:05not really doing anything a kind of like
9:07a resting area those types of cells are
9:10called stable cells so what are they
9:12called they're called stable cells now
9:15stable cells stable cells if we think
9:20about these guys they're okay with not
9:23having to replicate that often they
9:25replicate when the stimulus is strong
9:28enough when there's a strong enough
9:30stimulus so these guys don't necessarily
9:33replicate a lot but they can if the
9:35stimulus is strong enough like different
9:37types of growth factors to push them
9:39into the cell cycle so what are these
9:41different types of cells the liver oh my
9:44goodness the liver is such an amazing
9:45organ you want to know why because if
9:46you can now you can take a good portion
9:48liver almost 40% of the liver and what
9:51happens is let's say I cut 40% of my
9:53liver off my liver can regrow itself
9:56that's one of the beautiful things about
9:57the liver there's different types of
9:59growth factors that the actual liver
10:01cells will release to make more liver
10:03cells so your liver is real
10:05good I think the hepatocyte s-- within
10:08the liver are really stable self so
10:10let's put here patio sites alright so
10:14your have pata sites within the liver
10:15what else other ones is like your kidney
10:20tubules you know what the epithelial
10:21cells within the kidney tubules those
10:23are also stable cells but if we have a
10:26stimulus necessary to push them into
10:28going into the cell cycle they can so
10:30the epithelium of the kidney tubules
10:36okay like your proximal convoluted to be
10:39a loop of Henle all those different
10:40types of things right and then if you
10:42want even the alveolar cells of the
10:45lungs right now there's the last one and
10:49these are the ones that pretty much
10:50everybody usually knows you have a last
10:54one and these are called permanent cells
10:56so these cells once they go through the
10:59cell cycle they don't ever go into it
11:01again what are these again we said these
11:04are your permanent permanent cells and
11:10these ones are the usually the ones that
11:12people usually remember and in other
11:14words we call these they're a mitotic in
11:18other words they don't undergo through
11:19might they don't undergo mitosis these
11:21are your neurons so your nervous tissues
11:24alright so your neurons what else you
11:27know your skeletal muscle that's another
11:29one your skeletal muscle cells so your
11:31skeletal muscle and another one your
11:35cardiac muscle the one that's
11:37responsible for the heart so the
11:38myocardium right so the cardiac muscle
11:44so it's really important to understand
11:47the three different types of cells
11:49because some cells are going through the
11:51actual cell cycle very often labile some
11:54will go through the cell cycle if they
11:55have a proper and strong enough stimulus
11:57stable and then some of them will not go
12:00into the cell cycle and that is the
12:01permanent cells okay now that we
12:04understand that one thing we need to
12:07talk about for the g1 we make more
12:09organelles we synthesize proteins and
12:11enzymes but we got to do one more thing
12:12sometimes these cells can have certain
12:16types of
12:17damage they might have certain types of
12:19problems sometimes they call them five
12:22minima Dean dimers so in the g1 phase
12:25you want to be able to prevent or repair
12:30these things called thymidine dimers so
12:39you have different types of enzymes that
12:40can actually scan the DNA because you
12:42want to make sure that before you start
12:44replicating the DNA there's no stakes
12:46within the DNA so sometimes people can
12:48get Diamond Dean dimers and what you
12:50want to do is you want to repair those
12:51time adding diamonds before you get
12:52ready to replicate the DNA so in the gap
12:55one phase or g1 phase we make more
12:56organelles in the cell we make more
12:58proteins and enzymes to help to
13:00replicate the DNA and we repair any
13:03thymine dimers that when we go into DNA
13:04replication there's no mistakes
13:06previously okay and the reason why
13:09you're making more organelles why
13:10because you only have right now
13:11organelles for one cell you need to make
13:13organelles for two cells that's the
13:15whole purpose there okay from the g1
13:18phase where does it go into it's gonna
13:21go into this next phase the S phase the
13:25S phase stands for synthesis so this is
13:28the synthetic phase the synthetic phase
13:32or the ass phase now what happens in the
13:36S phase we've kind of already talked
13:38about it right what we're doing here is
13:40we're taking a cell all right let's say
13:43I take this cell and I take the genetic
13:45material you know there's the genetic
13:46material right here let's say I'm taking
13:48this genetic material here's the DNA
13:50what am I trying to do with this DNA I'm
13:53trying to we'll talk about this in a
13:54separate video but what I want to do is
13:56I want to take this DNA I want to open
13:58it up so I want to open the DNA up and
14:01form what's called a replication bubble
14:02all right you get this thing called a
14:04replication bubble and then what happens
14:07is I want to be able to synthesize new
14:10DNA based upon whatever nucleotides I
14:13have here so I'll make a whole new
14:14strand and this is going to be what's
14:17bio it's called the semi conservative
14:19model so what I want to do in this phase
14:22is I want to take and replicate that DNA
14:24so in this phase the primary thing that
14:26is occurring is going to be DNA
14:31replication what's really cool about
14:34this DNA replication is it's maintained
14:37by specific types of enzymes there's
14:40what's called DNA polymerase a--'s and
14:45there's two types type 1 and type 3 now
14:49these enzymes are so good at their job
14:52so so good that generally they're
14:56replicating the DNA so fast but very
14:59faithfully they don't make that many
15:01mistakes you know sometimes they can
15:03make a mistake
15:05every million or billion base pairs
15:08that's insane so they don't make very
15:10many mistakes that often but we still
15:14want during this this synthesis phase we
15:16want to make sure that there was no
15:17errors in replication so sometimes there
15:19certain genes we'll talk about that and
15:21they're called tumor suppressor genes
15:23and and also DNA repair genes and we
15:27have other genes that can read the DNA
15:28we'll talk about all these things but we
15:31want to make sure that whenever we
15:32replicated the DNA that there's no
15:33errors so we're gonna want to fix that
15:35we'll talk about different checkpoints
15:36alright
15:37so synthetic phase RS phase we know what
15:42it's doing it's replicating the DNA all
15:44right so we're replicating the DNA and
15:47technically if you want to remember for
15:48replicating the DNA or going from 2 in
15:51in to 4 in right because we're taking it
15:56from a total of 46 chromosomes in one
15:58cell and doubling it and if we're going
16:00from 46 and doubling it you'll have 92
16:02chromosomes right and 46 will go to one
16:04cell 46 will go to the other cell that's
16:06the whole purpose here another thing is
16:09how long does this phase take we said
16:11that that one can vary from eight hours
16:12to years it depends on the type of cells
16:15but this one is usually constant in
16:18duration usually it's about six hours
16:21this phase usually is approximately
16:24about six hours okay so now we know the
16:28gap one phase and we know the S phase
16:31remember I told you though that before
16:33we go into the S phase we want to make
16:35sure that the DNA is okay because we
16:36don't want to waste energy and time on
16:38replicating DNA if it's not even good so
16:41what we'll talk about in another video
16:43and the regulation is there's a little
16:46checkpoint right here right here there's
16:49like a little checkpoint where we're
16:50gonna stop this cell and just check it
16:53to make sure everything is okay that
16:55checkpoint is called the g1 s-phase
16:59checkpoint and again we'll talk about
17:01the regulation through tumor suppressor
17:04genes and proto oncogenes and stuff like
17:06that but I just want you to get an idea
17:08of what's happening within the cell
17:09cycle
17:10okay so g1 in order for the go to S
17:12phase it has to have this checkpoint
17:13where we kind of check the DNA make sure
17:15that there's no issues make sure that
17:17there's enough proteins and enzymes or
17:18organelles for it to go and replicate
17:20after it replicates though now we have
17:23to we have a cell here right we have a
17:26cell at this point time now who not only
17:30he's actually going to be what he's no
17:32longer gonna be - in this cell is going
17:34to be four in total of 96 99 other thing
17:42we need to do here this next face
17:44there's g2 phase what color should we do
17:46let's do this one this is the g2 phase
17:51or gap - phase okay now in the g2 phase
17:58this one's kind of a simpler phase we've
18:01already done what to this cell we've
18:02already replicated the DNA we've already
18:04made more organelles alright so let's
18:08just assume that those are ribosomes we
18:10had one we went to two we had a
18:12mitochondria right here and what do we
18:15do we went to two so we already made
18:18more enzymes we made more organelles we
18:21replicated the DNA we checked for any
18:23types of damage now what do we got to do
18:25is this enough cytoplasm is this cell
18:28big enough to split into two equal cells
18:30has to be perfect right our cells are
18:34very particular right so because of that
18:37we want the cell to grow in size so in
18:41this phase the main function of this
18:43phase is primarily focused on cell
18:46growth that is its primary function the
18:50primary function of this phase is to
18:52regulate cell growth by doing what
18:54increasing the cytoplasm
18:57and the different types of components
19:01within the cell to make it big enough
19:03that whenever we pinch these two this
19:05one cell into two cells it's equal we
19:08want it to be perfect okay so what are
19:10we up to now we did gap one we did S
19:14phase we've done gap to face our G to
19:17face these three make up a whole phase
19:22if you will and that whole phase is
19:25called interphase so again I want you to
19:27remember interphase is made up of to
19:31come up sorry three components what are
19:33those three components one is g1 the
19:37next one is s and the last one is g2 and
19:41in order it goes g1 - ass ass - G - okay
19:48now and remember remember that one point
19:51right here before we go - from g1 to s
19:53you have to have a g1/s checkpoint okay
19:59and we'll talk about that in the
20:00regulation of cell cycle now we finished
20:03the interface we have to talk about
20:05something else now now we have to go
20:07into what's called mitosis the M phase
20:11so again let's come up here and write up
20:14here mitosis mitosis are sometimes they
20:19refer to it as the M phase in mitosis
20:23you have to remember that there's
20:25specifically four parts and there's
20:28technically a fifth part in there we'll
20:30discuss it but you're gonna have P
20:32mapped okay P matte and there's another
20:37one here which is going to be
20:38cytokinesis that's kind of a part of
20:40telophase we'll talk about it but P is
20:42for prophase M is for metaphase a is for
20:48anaphase and t is for telophase and
20:52there's a part here which we'll discuss
20:54which is like the end of telophase which
20:56is called cytokinesis where we'll
20:59separate the cytoplasm equally so let's
21:03go through the first part here prophase
21:05okay so here's what you have to remember
21:08when we were going through this wrap
21:10location this whole interface the
21:13genetic material inside of the cell so
21:15what is this inside of the cell what
21:17should you have inside of it you should
21:18have a nucleus right but inside of the
21:22nucleus it was has a bunch of different
21:23it has a lot of DNA
21:25the thing is though the DNA originally
21:28was really loose it was loose DNA we
21:32also call this loose DNA call it you
21:34chromatin but here's the thing in order
21:38for us to be able to separate the DNA
21:40properly the chromosomes we don't want
21:43it to be loose we want to condense that
21:45chromatin so what is this first phase
21:47here this first phase here is called
21:49prophase
21:50okay so prophase and again what did we
21:53say we said that the actual chromatin
21:55what is chromatin how would you define
21:57chromatin chromatin is actually two
21:59basic things one is it's your DNA and
22:03the other one is your histone proteins
22:05will talk about these when we talk about
22:07how DNA is organized into what's called
22:09nucleus ohms but there's many different
22:12types of histone proteins but all
22:13chromatin is is we're taking DNA and
22:16wrapping it around these histone
22:17proteins like octamer x' of them so what
22:20I want to do is I want to condense that
22:22chromatin so let's condense that
22:23chromatin now and when I condense it
22:26you're gonna get something which is
22:27going to look kind of like this it's the
22:29easiest way to represent it you're gonna
22:31see what's called these chromosomes so
22:35you're gonna see these chromosomes and
22:37they're gonna be nice and condensed so
22:41there's my chromosomes now what did I
22:43tell you a cell has to have it has to
22:46have a nucleus but here's the thing if I
22:50want to I've already duplicated the DNA
22:51right because before it would look like
22:53this pretend here was the cell before it
22:55was going in it would look like this it
22:58would have before it would only had one
23:00chromosome right before I went to the S
23:02phase then after the S phase it would
23:04actually replicate and make two
23:05chromosomes now from here we want to be
23:09able to separate these chromosomes into
23:11opposite ends into two cells so should
23:14we have a nucleus blocking it now
23:16because if I have the nucleus blocking
23:19this there's no way I'm gonna be able to
23:20separate these into two ends of the cell
23:21so guess what the nuclear
23:23envelope is actually going to get
23:27dissolved there are special types of
23:29cyclin dependent kinases and things like
23:32that that will phosphorylate different
23:35proteins of the nuclear envelope like
23:37for example they'll phosphorylate like
23:40lamins
23:41they'll phosphorylate some of the
23:43histone proteins like h3 a there's even
23:46other proteins here too that they can
23:47phosphorylate that are a part of the
23:50nuclear envelope right so different
23:52parts of the nuclear envelope it's going
23:54to phosphorylate these guys and when you
23:56phosphorylate them
23:58it sets up specific enzymes to break
24:00them down it activates certain proteases
24:03so there will be some specific enzymes
24:05that will phosphorylate different
24:08proteins of the nuclear envelope like
24:11lamins and histone proteins and other
24:13different types of proteins and cause
24:15them to get degraded by proteases so the
24:18nuclear envelope is gonna start
24:19dissolving what else is gonna happen you
24:22know you have these other things here
24:24right you start seeing these these
24:28structures that are part of the
24:29cytoskeleton and these aren't here
24:33you're gonna start forming these things
24:35called your microtubule organization
24:37center you know have these things called
24:38centrioles so you have these things
24:40called centrioles and these centrioles
24:43are gonna be important for forming
24:44what's called the microtubule
24:46organization Center so what is these
24:49things right here called these are my
24:52microtubule organization Center M TOC
24:56microtube the organization Center so
24:58three things have happened one thing i
25:00condensed the chromatin second thing I
25:03start dissolving the nuclear envelope
25:06the third thing I start seeing the
25:08appearance of these things called
25:10centrioles or centrosomes and it's going
25:13to be we're gonna call them the
25:14microtubule organization Center because
25:16from these the actually gonna have these
25:18things called polar and astral
25:20microtubules guess what they do they
25:21connect to the chromosomes to help to
25:23separate them
25:24okay so we got prophase that's the first
25:26part now we go to the second part the
25:29second part is going to be metaphase
25:34now in metaphase what happens here
25:37you're gonna have the nuclear envelope
25:40should now be dissolved right but what's
25:43gonna happen is remember that
25:45microtubule organization Center it's
25:47gonna start going towards during this
25:49process of where we get to metaphase the
25:53microtubule organization centers start
25:55taking up residence in the opposite ends
25:57of the cell the different poles of the
25:59cell so one will see right here and the
26:04other one will see it the opposite pole
26:05of the cell so here's the one pole to
26:07cell here's the other one what did I say
26:09comes from these organization centers
26:11these microtubule organization centers
26:12these different microtubules you know
26:15there's microtubules that go to where
26:17the actual chromosomes are and there's
26:18ones that actually come off like this
26:20those are called your astral
26:21microtubules and these are your polar
26:23microtubules now what do we say should
26:26be in here we should have the
26:28chromosomes so let's actually show here
26:30here is our chromosome we're here we'll
26:33have another one here right so here's
26:37our chromosomes now since we have the
26:40chromosomes what should be connecting
26:43the chromosomes to these actual micro -
26:47of organization center we should have
26:48these microtubules connecting here now
26:52we need to come up with a little
26:54definition here because sometimes people
26:55get confused alright so a chromosome
26:59when we talk about a chromosome it's
27:02actually right here here's a chromosome
27:05right so chromosome how would you define
27:07a chromosome a chromosome again is
27:09actually made up of chromatin DNA and
27:10histone proteins so like in this I'm
27:12gonna have DNA moving in throughout it
27:16right but a chromosome has a short arm
27:19and a long arm right so it usually the
27:21short arm is up on top long arm on the
27:23bottom right but more important part the
27:26ends of it the ends of the chromosome is
27:29called your telomeres this is a telomere
27:31and this is a telomere and the center of
27:36it is what's called your centromere the
27:40centromere determines the number of
27:42chromosomes you have so for example
27:45let's pretend I'm get I'm just going out
27:48there with this how many chromosomes do
27:53I have one even though this thing is a
27:56freaking freak of nature it's still one
27:58chromosome because we determine the
28:00number of chromosomes by how many
28:01centromeres we have but a better way of
28:04describing this is we take that
28:05replicated part here right so pretend
28:09here and here was the old DNA well
28:12generally it's actually actually that's
28:14wrong because if it's if we actually
28:16replicated it it should be by the semi
28:18conservative model right so we should
28:20have old and new mixed in so here I have
28:23one strand that's the old strand
28:25here's another old strand and then what
28:28should you have here you should have a
28:29new strand and a new strand this is one
28:34chromosome but the two individual
28:36components of that chromosome what do
28:38you call these two little things here
28:40what is this guy and what is this guy
28:42these are called sister chromatids okay
28:49sister chromatids but this whole thing
28:52is a chromosome all right the whole
28:54thing is a chromosome but these two
28:57individual entities is the sister
29:00chromatids but this whole thing is a
29:02chromo so all right so just so we
29:06understand it I wanted to make sure that
29:07we really get an idea of that okay so
29:10now we're going back to metaphase so
29:14from here these polar microtubules what
29:17are these guys right here these are
29:19called your polar micro tubules
29:24here's your chromosomes and here's your
29:27microtubule organization Center the
29:30microtubules are now connected to the
29:32chromosome we got actually be specific
29:34at what part of the chromosome what we
29:36said we had the centromere right so if
29:38we said here we had chromosome
29:41chromosome like this there's a protein a
29:44protein structure that's right on the
29:47outsides of it right here you know what
29:50that structure is called that that
29:52purple structure they call that the
29:54kinetochore canítö
29:57or it's a protein structure and guess
30:00what connects to the kinetochore the
30:02microtubules those polar microtubules
30:04they connect to the kinetochore imagine
30:07them like a hook right because what
30:09they're gonna do is they're gonna hook
30:10one sister chromatid hook the other
30:12sister chromatid and separate the
30:13suckers right so what we need to do is
30:16is we have to have these polar
30:18microtubules connecting to what
30:20structure again what's this purple
30:21structure the kinetochore okay
30:24now once they're connected at the
30:27kinetochore you're gonna notice
30:28something I've only drawn to here but
30:31imagine there was tons of these bad boys
30:33all of them lined up in a row and
30:35they're lined up kind of like along this
30:38mid line if you will they're kind of
30:40lined up or along this mid line or
30:42another way of saying it is on the
30:44metaphase plate so they're aligned very
30:50very perfectly all of them are aligned
30:53perfectly what are we gonna do now okay
30:55now we've set up the stage to start
30:58separating them okay so a metaphase we
31:01aligned them up on the metaphase plate
31:02we have the polar microtubules are
31:04connecting to the kinetochore of the
31:05chromosomes and we're gonna separate
31:08those sister chromatids okay so now it's
31:10going to the next step
31:12the next stage is anaphase you can
31:15remember away so sometimes how they
31:18remember this is metaphase in the middle
31:20or metaphase plate anaphase is their
31:22going away from one another right so
31:24what should I have over here again I
31:26should have my microtubule organization
31:29center all right microtubule
31:32organization Center and then what should
31:35I have coming over here and connecting I
31:36should have will draw three this time
31:39since we only did two last time what
31:41should I have it connecting to let's say
31:42right here I'm going to have my
31:48chromatids because what am I going to do
31:49remember that centromere there I'm going
31:52to split the two I'm going to split the
31:55two there's a protein that's connecting
31:56them together called cohesin I'm gonna
31:59split the cohesin and there's a special
32:01regulation point of that I'm gonna split
32:03the cohesin so I can take this sister
32:05chromatid go to this pole this sister
32:07chromatid go to that pole so now look
32:10here
32:10chromatid is gonna be coming over here
32:14this chromatid is gonna be coming over
32:16here but really this is a chromosome the
32:18sister chromatids were separated but now
32:20how many central means do I have one so
32:22that's a chromosome then what do I have
32:24over here another chromosome what do I
32:26have over here another chromosome
32:28another chromosome so now what am i
32:30doing I'm separating the chromosomes for
32:32one another because eventually I want
32:34all these chromosomes to go to this end
32:36I want all these chromosomes to go to
32:37this end because originally what was
32:39this whole thing for in there's a total
32:42of 92 chromosomes
32:43I need 46 of them to go to one end 46 of
32:46them to go to the other end so that's
32:48what we're doing here it's just so darn
32:50cool all right so we're separating these
32:52two opposite into the pole so where will
32:54these guys be going they'll be going
32:56this way now an important concept here
32:58we're not gonna go into super depth on
33:00them but how the heck do they get there
33:02that's how important thing with science
33:05is you have to ask yourself the question
33:06sometimes why are these things happening
33:08so you know there's different types of
33:10proteins here I call them motor proteins
33:12so special types of motor proteins we're
33:15not like I said we're not gonna go into
33:16super depa that's once you get the idea
33:18there's motor proteins and these motor
33:21proteins can literally walk along the
33:24microtubules carrying whatever structure
33:26they have with them towards a specific
33:29direction isn't that cool
33:30so there's different motor proteins that
33:33can move these microtubules towards the
33:38actual microtubule organization Center
33:40to the opposite ends of the poles what
33:42are these things called again they're
33:43called motor proteins there's
33:48particularly too in this situation one
33:51is called dining and the other one is
33:54called kinesin technically this is a
33:57minus in directed motor protein and this
34:00is a plus and directed motor protein I'm
34:02just throwing out there you don't
34:03necessarily have to know this I just
34:05want you to get the idea that there is
34:06two motor proteins dynein and chi Nissen
34:08and what are they doing they're helping
34:10to move these actual chromatids towards
34:14the microtubule that's important so now
34:17we've done anaphase we've separated the
34:19actual chromosomes
34:21now once we've done that what do I need
34:25to do I need to equally distribute this
34:27into two cells so what this cell starts
34:29doing you have different types of actin
34:31and myosin proteins here let's put here
34:34you have these different types of actin
34:36I'm going to represent this with like
34:37red here's some myosin proteins or
34:39contractile proteins here's some myosin
34:42proteins which are contractile proteins
34:44and then let's say near it we have some
34:46actin molecules so here's some actin
34:49molecules which are contractile proteins
34:50these guys start contracting the cell
34:53and they produce this little
34:56constriction ring so we're gonna try to
34:58take this cell and just squeeze it when
35:01I try to squeeze it to push this stuff
35:03into the amount of stuff and equally
35:05into both cells I produce this little
35:07constriction ring but they don't like
35:09that name they call it a cleavage furrow
35:12they call this right here a cleavage
35:16furrow okay and it produces this thing
35:22called the constriction ring now it
35:23looks like I'm getting ready to have two
35:25cells all right so now what am I gonna
35:29do remember what we had before we didn't
35:32have a nuclear envelope guess what we
35:33start forming again guys I don't know
35:35why I get so excited about this stuff I
35:37just think it's so cool but you start
35:39actually beginning to reform your
35:42nuclear envelope so now you want to get
35:45ready for this cell to be complete so
35:48you start reforming your nuclear
35:50envelope you start pinching and forming
35:52this constriction ring called the
35:53cleavage furrow through myosin and actin
35:55proteins then what what should you have
35:57over here you should have your
36:00chromosomes how many should be over here
36:02there should be a total of 46 here right
36:05or we say 2n how many should be over
36:08here a total of 46 we say 2 in and that
36:13cool what else should you have over here
36:14you should have an equal amount of
36:16ribosomes you should have an equal
36:19amount of ribosomes I'm only gonna do a
36:21couple things but you I want you guys to
36:22just get the idea and then what else you
36:25should have equal amount of mitochondria
36:28we're separating these cells just
36:30perfectly our body's amazing now
36:34before we end this off what else do you
36:38have in this cell
36:39what's pretty much the fluid in the cell
36:41we already talked about rember there's
36:42three parts of the cell cell membrane
36:44nucleus cytoplasm the cytoplasm is all
36:47the fluid all the fluid of this cell so
36:51now we want to be able to distribute the
36:53cytoplasm evenly between the two cells
36:55so whenever we do and we finish this
36:58process we're gonna squeeze that
37:00constriction ring completely together
37:01cause these actual membranes to fuse and
37:05equally distribute the actual cytoplasm
37:08here's one more thing right so we said
37:10how we've squeezed the cytoplasm equally
37:12into both cells which is the cytokinesis
37:13process right we produced that
37:14constriction ring and we said that the
37:16nuclear envelope starts reforming well
37:19you see how we said that we have these
37:20chromosomes here right we equally
37:21distribute the chromosomes something
37:23else happens before they were condensed
37:25but guess what they need to become loose
37:28again so the chromatin starts actually
37:31becoming a little bit more loose again
37:33so now we can see it like this in the
37:37telophase right so now we're gonna have
37:39this loose chromatin all right now after
37:44we've pinched these actual cells off
37:46right we've equally distributed the
37:48cytoplasm what does that call it again
37:49whenever we pinch the cells and we
37:51actually form that constriction ring
37:53eventually separate the cytoplasm
37:54equally it's called cytokinesis right
38:00that's an important part now we've
38:04pinched this cell so really we should
38:06have two cells here we should have two
38:08cells and these two cells should have an
38:12equal amount let's assume that their
38:14actual nuclear envelope completely
38:17reformed so here's a nuclear envelope
38:18here's the nuclear envelope on this one
38:20and what should you have in there you
38:23should have the chromatin right you
38:25should have the chromatin and this
38:27should be a total of how many
38:28chromosomes 46 chromosomes which means
38:31it's 2n 46 chromosomes here's which
38:33should be two in now even though these
38:35cells aren't perfectly identical in size
38:38they should have the exact same amount
38:40of cytoplasm and the same amount of
38:43organelles all right guys so we said
38:45that we're going to take a look at the
38:47phases of the cell cycle just a models
38:50right kid getting a different look at it
38:51so if you look here the first one we
38:53said his interface and interface was
38:54consisting of the three parts right g1 s
38:57g2 easiest way to identify it again is
39:00if you remember what was happening here
39:02you see how the chromatin is really
39:03loose within the nucleus right it's
39:05really really loose and again what
39:07should have happened by now within at
39:08the end of interphase at least you
39:10should have actually replicated the DNA
39:12so now it's no longer to in but it
39:14should be for in in this cell now
39:16another thing is actually after we get
39:19done with this interface we're gonna go
39:21into the next phase which is prophase
39:23now in prophase what's gonna be really
39:26different with this one look here you
39:28see how the crewmates chromatin is still
39:29really kind of loose here well another
39:31thing that should happen is that the
39:32nuclear envelope should actually start
39:34breaking down the lamins and condense
39:36and proteins all the things that are
39:37making the nuclear envelope up remember
39:39we're gonna phosphorylate those proteins
39:40other proteins will phosphorylate is
39:42like the histone proteins and then what
39:45did we say again what are these guys
39:46right here these are the microtubule
39:49organization Center remember we have the
39:51centrosome and then we have the
39:52microtubules that are beginning to form
39:53here then from the prophase we can
39:57distinguish it different from metaphase
39:59how remember what we said as we go from
40:02prophase to metaphase the mitotic
40:05spindles right those microtubule are an
40:07organization centers start taking
40:08residence up in the opposite poles of
40:11the cells and then those microtubules
40:14the polar microtubules start connecting
40:16to the chromosomes along this midline of
40:19the cell which is called the metaphase
40:21plate right then after that if
40:24everything is successful at that
40:26checkpoint the EM checkpoint there's a
40:29protein we'll talk about them in the
40:30regulation video it's called
40:31APC and he'll help to initiate this
40:34segregation or the separation of these
40:36chromatids from one another when they
40:38start separating from one another let's
40:40go over here because now we're in the
40:41next phase anaphase anaphase remember
40:44here's those mitotic star the
40:45microtubule organization centers and the
40:47microtubule are connected to those
40:48chromatids and they're pulling the
40:50chromatids to opposite poles of the cell
40:52this one's pulling it up this one's
40:54pulling it down this is how you can
40:56distinguish anaphase for the last and
40:59final phase we're assuming that the
41:01kids and all the organelles and all the
41:03cytoplasm is getting equally distributed
41:05into the two different cells right but
41:08then you produce this little contractile
41:09ring or this constriction ring which
41:11produces this thing called a cleavage
41:12furrow right but we want to equally
41:15distribute all the different cytoplasmic
41:16contents into both cells which is the
41:18cytokinesis process right so what do we
41:21have here again you can notice the two
41:24cells that we're trying to form t-to
41:26telophase right we're trying to form two
41:28cells another thing is what do you
41:30notice here
41:31what's happening with the chromosomes
41:32right the chromatin is a little bit more
41:35loose again
41:36where here was condensed now it's a
41:37little bit loose also the nuclear
41:39envelope should be reforming and again
41:41look for that cleavage furrow and that's
41:44how you can identify telophase all right
41:46so again real super quick recap what are
41:48these phases of the cell cycle again
41:51it's interphase prophase metaphase
41:53anaphase and telophase these cells that
41:58we just replicated what can they do well
42:01some of them guess what they can go
42:04right back into the cell cycle right
42:06back into g1 some of these cells which
42:09type of cells is the proliferative cells
42:11the lab aisle cells this the epithelium
42:14of the skin the GI tract the urinary
42:16tract amout of we text em cells they can
42:18go right back into the cell cycle but
42:20some of the cells they don't really go
42:22back into the cell cycle they go into
42:25another area so they kind of go into
42:27this are their area where they wane a
42:29little bit what is this area called this
42:32area is called the quiescent so they
42:36call this g0 right just called g0 phase
42:40or we also called the quiescent phase
42:45and this is where the cells go to rest
42:49so they can rest in this phase they
42:52don't have to go into any type of
42:54replication they can remain dormant if
42:56you will but then let's say that there's
42:59a stimulus some type of stimulus
43:00whatever it might be there's a stimulus
43:02to this cell and the stimulus is strong
43:05enough to put it back into the cell
43:06cycle to go back into G you want to
43:08start undergoing the cell cycle those
43:10could be some of those stable cells but
43:12there's other cells that no matter what
43:14one
43:14they're done they're a mitotic those are
43:17your neurons your schedule your cardiac
43:19muscle
43:19they're not gonna proliferate anymore
43:22another thing that can happen with this
43:24cell cycle is you know as you get older
43:26as we get older remember we had that
43:28chromosome right here right here's our
43:31chromosome and as we get older remember
43:35these were the telomeres these ends up
43:37here as there's consistent DNA
43:40replication after DNA replication either
43:41DNA replication the telomeres start
43:44getting shorter over time so as you age
43:47as we get older so with age that's a
43:49terrible marker as we get older with age
43:52during the aging process what happens to
43:57the telomeres this causes the telomeres
44:00to shorten and sometimes because of that
44:06these cells can go into what's called
44:10cell citizens where they are
44:13irreversibly out of the cell cycle they
44:16can't enter into the cell cycle no
44:18matter what so sometimes in situations
44:20as people get older their telomeres
44:22shorten and shorten and shorten as a
44:25result some of these cells with their
44:27telomeres are shorter and shorter and
44:29shorter we put those cells into an
44:31irreversible state to where they can't
44:34enter into the cell cycle that's called
44:35cell citizen's okay so we've covered
44:38these cycles and we said that there's a
44:40g1/s checkpoint I should also say that
44:43there's one other check point two other
44:45checkpoints so we said that we had the
44:47g2 phase and we said the times this
44:49phase is approximately about two hours
44:51about two hours just to throw that out
44:53there and in Phase is probably about the
44:55time that you guys have almost watched
44:56this video about an hour so by the time
44:58of this video isn't over you guys have
45:00almost undergo mitosis that's kind of
45:04cool but anyway there's an actual
45:06another checkpoint this next checkpoint
45:09is right here as you're going from the
45:11g2 phase into the M phase so about right
45:16here there's another checkpoint this is
45:19called the g2 M checkpoint
45:23we need to make sure that there was no
45:26mistakes in the DNA replication process
45:28because again even though these DNA
45:30polymerases are very very faithful and
45:32they're very good and they only make
45:33mistakes by very one two out of a
45:36hundred thousand million base pairs we
45:39still need to make sure that there was
45:41no damage and there's special genes that
45:43do that called ATM genes and we'll talk
45:44that they produce proteins that read the
45:46DNA but we have to regulate it at that
45:49checkpoint where's another one you know
45:52right here at metaphase right here
45:54before we get ready to go into anaphase
45:56there's another checkpoint before we get
45:59ready to separate these chromosomes we
46:01have to make sure that these guys are
46:04aligned at the metaphase plate perfectly
46:06we need to make sure that there's no
46:06mistakes here and this checkpoint is
46:09called the EM checkpoint and we'll talk
46:14about the proteins like the APC proteins
46:16secure in all those different proteins
46:18that help to ensure that from that point
46:21on everything has occurred successfully
46:23and properly measure so if you guys have
46:25watched this video I really hope that
46:27you guys now understand the cell cycle I
46:29truly do it's our goal here in
46:31engineering science to help this stuff
46:33make sense for you guys so if you guys
46:34did please hit that like button comment
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46:49Arion engineers as always until next
46:51time
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47:14you
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