So the next component of the cell
that we're going to discuss is the nucleus.
And the nucleus is the most important
of the organelles because it allows
for us to actually function and so I
refer to this as the "brain" of the cell.
Inside of the nucleus, we have our
hereditary units of the cell, or our genes.
Our genes are located on a molecule
called DNA and it is in these genes that encode
everything that we need in order
to perform all of life's functions.
The genes are arranged along
chomosomes that are found inside of our cells
and our DNA is so long that these
chromosomes allow for all of these information
to fit inside of the nucleus.
So in discussing the nucleus, it's important to discuss
exactly how a cell cycles or the life of a cell.
So the cell, if you think about it like a
clock, the cell spends most of its time
in a part of the cell cycle
known as interphase.
In interphase, there are certain processes that
are going to occur at different steps in interphase.
Interphase is divided into three sub-phases.
G1 being the phase where normal
cellular processes are occuring
and as well where the cell
begins to prepare to divide.
Why does the cell need
to divide in th first place?
Remember, in life's basic
processes, growth is essential.
It is a requirement for all living things and so cell
division allows for organisms such as humans to grow.
So in G1, we prepare to grow
by doubling in size as well as
doubling the number of organelles
that are found inside of the cell.
From there, we go to S phase.
An S Phase is when we
double the amount of DNA.
Why do I need to double the amount of DNA?
Again, I'm going to create
two cells from originally one cell
so everything needs to be twice as big and
I need to have twice as much of everything
so that my new cell is
exactly like the other cell.
So after we go to S phase,
we then enter into G2 phase.
And G2 phase is what I like to refer to as
kind of like the proofreading and prep phase.
So before I divide, I need to make sure that the new
cell that I'm gonna make is exactly like the old cell.
I want to make sure that the DNA has
been copied correctly or replicated correctly
and I wanted to just make
sure that the cell is ready.
Once I go through the proofreading process, I can
then enter into the other part of the cell cycle
which is M Phase or the
mitotic phase of the cell cycle.
In mitosis, I'm going to start with
one cell and end up with two cells.
So one cell that is doubled in size
with double the number of organelles
will now become two identical cells.
It's very important to remember in mitosis
that the two cells are genetically identical.
That is the goal of mitosis and
that will become important later
when we talk about
reproductive cell division.
In mitosis, there are
basically four major steps.
We're gonna start with prophase
where we're preparing the cell to divifde
by creating these microtubule
or mitotic spindle fibres
that are going to eventually
be used to pull the cell apart.
In metaphase, all of our chromosomes
are gonna line-up single file across the cell
to what's known as the mitotic plate.
and this is going to allow for the
duplicated DNA because remember,
we duplicated in S phase so everything
is by two to be separated eventually.
In anaphase, those mitotic spindle
fibers are now going to separate
those two duplicated
chromosomes away from each other
and pull them towards
opposite poles of the cell.
And then finally in telophase, we begin to start the
formation of new cells as well as an entirely new nucleus.
After the mitotic phase,
we go through cytokinesis.
Cytokinesis is actually separate from
mitosis and involves the actual separating
of the two nuclei that we just
made during during mitosis.
Cytokinesis is usually
gonna start during telophase
and eventually you end up with
two genetically identical cells.
So when it comes to cell division, remember I said
it's important for our cells to be able to divide
but what are the possible
destinies of the cell division?
Well first off, some of our cells
actually are non-dividing cells.
Examples of non-dividing cells in
your body include your muscle cells.
So believe it or not, all of the muscle
cells in your body are the same muscle cells
that you had when you were born.
And instead of getting new muscle
cells, the muscle cells that you already have
just get bigger and bigger
and bigger as you grow.
Other types of cells that are non-dividing
also includes certain types of nerve cells
which is why when you
destroy or sever a nerve,
it can lead to paralysis because there's
no process to replace those types of cells.
Another destiny of our cells
is to grow and divide normally.
And then finally, a third destiny which is actually
a very important destiny of your cells, is to die.
We actually need our
cells to be able to die.
We need old cells to die when they are
no longer useful or if they become defective
and as well actually during
the developmental process,
when we are developing from
an embryo and turning into a baby,
there's going to be an interplay
between cells growing and dividing
and also between cells dying.
So for example in the womb,
your fingers and toes are webbed
and then as you begin to develop,
the cells in between the digits
began to die and we get individual fingers.