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0:04
We talked a lot
about the role of
the CDKs in G1 phase or
the cell responsive phase,
how they interpret the
extracellular signals
and help drive the
cell into the S phase,
into the autonomous phase.
But the cyclin CDKs are also
involved in the cell
autonomous phase.
They are the hammers that
will stop the cell cycle
in response to the
DNA damage errors
or the mitotic errors.
0:29
We know that just to
review the pre-replication
complexes,
assembled in G1,
that means all the
proteins that will sit
on the origins of replication
in our DNA waiting for that
signal to start replicating.
And that signal is
really the cyclin E,
cyclin A, CDK2-dependent
signaling.
They actually will phosphorylate
members of the pre ARC complex,
allowing that
replication to begin,
elongation will
happen and then as we
get to M-phase when
we're starting to
replicate the cell to
undergo cytokinesis
that also requires CDK activity.
The CDKs are really
integral in catalyzing
the sequential
activation of all of
the steps from S-phase
through M-phase.
1:18
Here's an example of this.
You probably remember from
your earlier biology classes,
the mitosis phase,
we start from an interface
style which has disordered
DNA in the nuclear membrane
and then we have the
different phases of mitosis,
from prophase all the
way to telophase.
In prophase, the chromosomes
start getting condensed so
that they will not
get broken during
mitosis, then during metaphase,
they're going to
get separated and
lined up on the metaphase plate
so that as the cell and
telophase undergoes
that separation,
pulling the chromatids to
either side of the cell,
getting ready for
the closing off of
these two new birthing, these
two new daughter cells.
CDKs trigger all the
steps in this process.
They trigger chromosomal
condensation,
they trigger nuclear
envelope disassembly,
so that the mitotic spindle
can actually get
to the chromatids
and they trigger the assembly
of the mitotic spindle itself.
Conversely, they
also trigger all
of the steps that
finish this process,
so the chromosome
decondensation as
the chromosomes fall out
of that chromatid state,
the nuclear envelope
has to be reassembled,
and then the spindle
has to be disassembled
and cell-cycle signals
in a stepwise fashion,
catalyzing each of these steps.
Their importance is emphasized
as we move through
the cell cycle.
