Previously, you learned about cell communications.
Now, we're going to take a look at how some of those communications
manifest themselves in the cell cycle and its controls.
By the end of this lecture, you should be able to
describe the main events of each phase of the cell cycle
as well as have an understanding of its checkpoints and
illustrate how those work.
In addition, you'll have some idea of how
failure of these checkpoints, failure of these cell cycle controls
could result in uncontrolled cell division or cancers.
So let's begin by looking at the cell cycle itself.
You're probably familiar with mitosis and interphase.
Interphase is the green portion of this cell cycle.
And mitosis and cytokinesis are in the blue portion.
Mitosis and cytokinesis are a relatively
short part of each cell's life.
It spends most of its time in other portions of the cycle,
So, mitosis, cytokinesis. Right after mitosis and cytokinesis,
the cell is half the size that it used to be
and so it needs to grow to its regular size. So Gap 1 phase
or growth phase 1 is about cell growth back to its normal size.
Now if the cell is fated to divide again,
then we might move forward in the cycle.
However, most cells don't divide and then divide immediately again.
They'll spend quite some time in the Gap 1 phase.
For example, if we were looking at muscle tissue or neurons
in the brain or fat cells, they're really not going to divide again.
And so when a cell is not going to divide again,
we might call it G0 even
because they are not going to move all the way
through the Gap 1 phase.
Towards the end of the Gap 1 phase,
we're beginning preparations for synthesis of DNA,
getting ready to duplicate those chromosomes
so that we have two copies
in order to move into cell division
and separate those copies into other cells.
So in S phase, or synthesis phase,
is where we have DNA replication occur.
We're going to cover the details of DNA replication
in a future lecture.
But for now, once replication has occur,
we have two copies of each chromosomes,
we move into the G2 phase. And in G2,
all the mechanisms that need to come into place for cell division
are being produced by the cells. So G2 is completed,
and the cells can then move into mitosis and cytokinesis
and the cycle continues, with a pause perhaps in the G1 phase.