Regulation of the Cell Cycle

Regulation of the Cell Cycle Watch me as a presentation or you will be sorry…

We already know that cells are growing and dividing in your body all the time Mitosis!

We need some mechanism to tell cells when to divide and when not to divide, so this process doesn’t get out of hand ONE DOES NOT SIMPLY DIVIDE ONE’S CELLS

There are two main types of regulatory mechanisms for cells • Internal regulators – proteins that respond to events inside the cell and then tell the cell whether or not to proceed with the cell cycle • External regulators – proteins that respond to events outside the cell and then tell cells whether to proceed and how fast to proceed

External Factors I REALLY WANT TO LIKE OTHER CELLS • Cells have molecules on their surface that signal other cells that touch them to stop dividing • This allows cells to fill available space but not become so tightly packed that the cells harm each other BUT THEN THEY TOUCH ME AND I’M LIKE “EW”

Internal Factors

Internal Factors • Cyclins are proteins in the cell that regulate the timing of the cell cycle • Each type builds during the cell cycle and peaks at a different time. • Only if there is enough of the correct type of cyclin will the next stage of the cell cycle occur

Internal Factors • For example, cyclin B triggers mitosis to begin. If there is not enough build up, the cell will not begin mitosis • The build up of each cyclin happens at a predictable rate, and keeps the cell growing and dividing at an appropriate pace

Internal Factors DON’T WORRY, I KNOW CYCLINS ARE HARD BUT YES, THEY WILL DEFINITELY BE ON THE TEST…

Cell Cycle Checkpoints • Now that you have a basic idea of the types of mechanisms that control the cell cycle, we can look at the three main points in the cycle that these mechanisms come into play • The three main checkpoints are at G1, G2, M • At each checkpoint, certain criteria must be met for the cell to go on to the next stage. • If those criteria are not met, the cell will go into G0, which basically means it is resting and not dividing at that time. • Most cells in your body are in G0 right now. Some, like nerve cells, never actually divide during your whole life!

What does the cell check for at each checkpoint?

Importance of each checkpoint? G1 checkpoint G2 checkpoint M checkpoint S G1 The G1 checkpoint is the most important. This is when a cell checks to see if it has the resources to divide and should therefore spend the energy to go through mitosis. Past this point, cells will most likely divide (because it has already invested the energy to copy its DNA). G2 M The G2 and M checkpoints are sort of “last resort” points. A cell will only be stopped here if the DNA is not properly copied or the chromosomes did not divide correctly resulting in possible damaged or defective new daughter cells.

So what happens if this goes wrong? ERROR AT G2 CHECKPOINT WE’RE ALL GOING TO DIE!!!!

Watch this animation of uncontrolled cell division https://www.youtube.com/watch?v=IeUANxFVXKc

Cancer Cancer is caused when any one cell loses cell cycle control and divides indefinitely. The accumulation of unneccesary cells then interferes with normal tissue or organ function. Because the control of the cell cycle is so multi-faceted, cancer can be caused by numerous different defects. Some examples: • A defect in any of the genes coding for cyclins • A defect in the cell’s ability to detect outside or inside stimula that may trigger cyclin production For these reasons, cancer is not a single disease that can be combatted with a single cure, but rather a general term for any cell cycle defect, each one requiring its own fix.

LET’S TAKE THESE CANCER CELLS Cancer Treatment • Treating cancer is challenging, because even though cancer cells are out of control, they are still human body cells • So killing cancer cells usually means killing some healthy cells along with them AND PUSH THEM SOMEWHERE ELSE

Regulation of the Cell Cycle