What is the cell cycle?

The cell cycle is the series of phases that a cell goes through to replicate, including interphase and mitosis.

Why is the cell cycle important?

It allows for cell replication, controls growth, and ensures the integrity of genetic material.

What are the main phases of interphase?

The main phases of interphase are G1, S, and G2 phases.

What happens during the S phase?

During the S phase, DNA replication occurs, preparing the cell for division.

Mitosis is a part of the cell cycle where one cell divides into two identical cells.

How is the cell cycle regulated?

The cell cycle is regulated by checkpoints that ensure proper growth, DNA replication, and division.

What occurs during prophase?

In prophase, chromatin condenses into chromosomes, and the nuclear envelope begins to dissolve.

What happens in metaphase?

Chromosomes align on the metaphase plate, preparing for separation.

What is the role of anaphase?

Anaphase separates the sister chromatids and pulls them to opposite poles.

What happens at the end of the mitosis cycle?

The cell undergoes cytokinesis, dividing the cytoplasm and resulting in two identical cells.

Cell Biology | Cell Cycle: Interphase & Mitosis

00:47:16

https://www.youtube.com/watch?v=LUDws4JrIiI

Résumé

TLDRIn this video, the process of the cell cycle, which includes interphase and mitosis, is broken down into comprehensible parts. Interphase consists of the G1, S, and G2 phases, where the cell grows, replicates its DNA, and prepares for division. The video further elaborates on each stage of mitosis - prophase, metaphase, anaphase, and telophase, culminating in cytokinesis, the final separation into two identical cells. Regulatory mechanisms like checkpoints ensure the fidelity of this process, spotlighting the importance of these cellular events for replication and growth control.

A retenir

🔍 Understanding the cell cycle is crucial for replication and growth control.
🔬 Eukaryotic cells are defined by having a cell membrane, nucleus, and cytoplasm.
📚 Interphase consists of G1, S, and G2 phases, each with specific roles.
🧬 DNA replication occurs in the S phase, preparing the cell for division.
⚙️ Mitosis is divided into prophase, metaphase, anaphase, and telophase, resulting in two identical cells.
🛡️ Cell growth control involves checks like the G1/S checkpoint, preventing errors before replication.
🧪 Prophase involves chromatin condensation and nuclear envelope breakdown.
📏 Metaphase aligns chromosomes on the metaphase plate for separation.
📈 Anaphase involves separating sister chromatids to opposite poles.
🔄 The cycle is regulated by cellular checkpoints ensuring proper division.

Chronologie

00:00:00 - 00:05:00
The video introduces the topic of the cell cycle, highlighting its importance for cell replication and growth. The basics of a cell are described, emphasizing the components of eukaryotic cells - the cell membrane, nucleus, and cytoplasm.
00:05:00 - 00:10:00
The G1 phase of the cell cycle is explained as a period where the cell grows by increasing organelles and synthesizing necessary proteins for DNA replication. Variability in the duration of the G1 phase among different cell types is discussed.
00:10:00 - 00:15:00
The video details labile, stable, and permanent cells, focusing on their roles in cell replication. Labile cells frequently undergo the cell cycle, stable cells replicate under certain stimuli, and permanent cells do not typically re-enter the cycle.
00:15:00 - 00:20:00
The video explains the G2 phase where cells continue to synthesize proteins and repair DNA in preparation for mitosis. Growth in cell size and cytoplasm occurs to ensure the cell is ready for division. A G1/S checkpoint ensures cells are ready to replicate DNA.
00:20:00 - 00:25:00
The S phase is discussed, where DNA replication occurs, doubling the genetic material. The video emphasizes the precision of DNA polymerases in copying DNA and mentions the role of tumor suppressor genes in ensuring DNA integrity during replication.
00:25:00 - 00:30:00
The M phase, or mitosis, is introduced, comprising prophase, metaphase, anaphase, and telophase. Prophase involves chromatin condensation, dissolution of the nuclear envelope, and formation of the microtubule organization center.
00:30:00 - 00:35:00
Metaphase is characterized by chromosomes aligning at the cell's equator with microtubules attached to their kinetochores. The video uses the term "metaphase plate" to describe the arrangement of chromosomes before being pulled apart.
00:35:00 - 00:40:00
Anaphase is the stage where sister chromatids are pulled apart to opposite poles of the cell. The process involves motor proteins like dynein and kinesin that facilitate the movement of chromatids along microtubules.
00:40:00 - 00:47:16
The video concludes with telophase and cytokinesis, where the cell divides into two, with nuclear envelopes reforming around separated chromosomes. The video's recap reinforces the phases and looks at cells entering a resting phase post-division.

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Carte mentale

Vidéo Q&R

What is the cell cycle?
The cell cycle is the series of phases that a cell goes through to replicate, including interphase and mitosis.
Why is the cell cycle important?
It allows for cell replication, controls growth, and ensures the integrity of genetic material.
What are the main phases of interphase?
The main phases of interphase are G1, S, and G2 phases.
What happens during the S phase?
During the S phase, DNA replication occurs, preparing the cell for division.
What is mitosis?
Mitosis is a part of the cell cycle where one cell divides into two identical cells.
How is the cell cycle regulated?
The cell cycle is regulated by checkpoints that ensure proper growth, DNA replication, and division.
What occurs during prophase?
In prophase, chromatin condenses into chromosomes, and the nuclear envelope begins to dissolve.
What happens in metaphase?
Chromosomes align on the metaphase plate, preparing for separation.
What is the role of anaphase?
Anaphase separates the sister chromatids and pulls them to opposite poles.
What happens at the end of the mitosis cycle?
The cell undergoes cytokinesis, dividing the cytoplasm and resulting in two identical cells.

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Sous-titres

Défilement automatique:

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