So now, we can look straight at interphase
and remind ourselves what goes on in G1S and G2.
G1 is purely the growth phase. After cell division,
a cell needs to grow and get back to its normal size.
It will hang out in G1 for quite some time,
may hang out in G1 for a long long time.
If it's never going to divide again,
we don't need to replicate DNA.
But if we are going to divide,
definitely we need to replicate DNA.
We need to take our one molecule of DNA
from our parent, mother and father,
and we need to replicate it to give each
a carbon copy or sister chromatid during S phase.
Then in G2, we're starting to think about
getting ready for actual cell division.
So things start to happen like assembly of the apparatus
that's going to help in cell division.
We start to see the centrioles forming, all the machinery
that's necessary for cell division to occur is built during G2.
Centrioles formed. Centrioles are the ones that are going to
sort of orchestrate the whole process of mitosis.
So centrioles, you can think of like the governors
of each of the poles of the new cells.
So they have to duplicate themselves
before this whole process starts.
So when we move into prophase, we've begun to wind up DNA.
It's packing into its chromosome form.
This started in late G2, but now moving into prophase,
we're starting to see formation of the mitotic spindle.
and chromosomes are packing.
So here we can see that we have
the nuclear envelope also breaking down
because in order to move chromosomes
and separate the sister chromatids
we need to get the nuclear envelope out of the way.
So the nuclear envelope breaks down during prophase.
The centrioles start forming these structures called asters,
which are stars. Aster meaning star.
And they start migrating towards the opposite poles of the cell.