So the question is what happens
when the cell cycle controls are broken?
You're probably familiar with the idea that
cancer results from uncontrolled cell division.
It's sort of like having a stucked gas pedal
or a broken break pedal.
So one of the genes that's of particular interest is the p53 gene
because it turns out it shows up in quite a lot of cancers.
The p53 gene is going to play a role in the G1S checkpoint,
so the checkpoint between growth phase 1 and synthesis.
And the role that it plays is in checking that DNA is in
good structure before we go through synthesis, so checking for errors
If there are errors, the p53 enzyme will correct those errors.
Sometimes the errors might be too big to correct
in which case the p53 enzyme does its job and says
"You know what, this is way too much for me to handle,
we cannot let the cell divide". So the p53 enzyme will
destroy those cells, so that they don't further their damage
and move on into the cell cycle. So this is a great example of
one of the proteins that's involved in the G1S checkpoint.
So in this case, p53 is considered a tumor suppressor gene.
In its normal form, it suppresses the growth of tumors
because it's checking the DNA and if things aren't right, then we
kill the cell, it's all over, that cell is not going to divide.
Only cells that are in good working order
would be allowed to go into S phase.
So many cancers have a broken p53 gene which means
it produces a non functional p53 protein.
With the non functional p53 protein,
we don't get the DNA checking that we should get.
And so what happens is there is no stop to cell division
and no DNA repair.
And if there is an error,
there's nothing to stop the cells from dividing.
And if we have enough errors developing in a particular cell
through certain rounds of cell division,
then this could develop into a cancer. So essentially here,
we have a gas pedal that's on, or a lack of a break pedal, right.
No break to slow it down, fix the repairs,
and make sure that unworthy cells don't move forward.
So p53 is a very important protein
involved in cell cycle control.