External Events
Other surrounding cells divide in order to cover up the gap left by the dead cells.
What is death of nearby cells?
This is a pause point where a cell checks that conditions are right before continuing division.
What is an internal checkpoint?
These two types of proteins work together to move a cell through each stage of the cell cycle.
What are cyclins and cyclin-dependent kinases (Cdks)?
These molecules act as brakes to stop or slow down the cell cycle when something goes wrong.
What are negative regulators?
Hormones that tell cells when to grow and divide.
What are growth hormone?
This checkpoint ensures the cell has grown properly, has enough energy, and has undamaged DNA before DNA replication.
What is the G₁ checkpoint?
This protein’s levels rise and fall in a regular pattern, controlling when the cell can progress through different phases.
What is a cyclin?
This checkpoint of the cell cycle is where most negative regulators, like Rb and p53, perform their function.
What is the G1 checkpoint?
When too many cells occupy one area, they receive a signal to stop dividing.
What is cell crowding?
This checkpoint confirms that DNA was copied correctly and repairs any damage before mitosis.
What is the G₂ checkpoint?
This process activates the Cdk/cyclin complex by adding a phosphate group.
What is phosphorylation?
This tumor-suppressor protein detects DNA damage, pauses the cell cycle for repair, and can trigger cell death if the damage is too severe.
What is p53?
Large cells can’t function efficiently, so they’re triggered to divide when this happens.
What is cell size control?
This checkpoint ensures all sister chromatids are properly attached to spindle fibers before the cell divides.
What is the M checkpoint?
These molecules act as brakes in the cell cycle, stopping it when errors or unfinished steps are detected.
What are Cdk inhibitors?
This protein binds to transcription factor E2F to prevent the cell from entering S phase until it grows large enough.
What is Rb (Retinoblastoma protein)?