Final answer:
Checkpoints are the molecular brakes that stop the progression of the cell cycle until the proper signals are received to continue.
Step-by-step explanation:
A checkpoint is a point in the cell cycle at which the cycle can be signaled to move forward or stopped.
The molecular brakes that stop the progression of the cell cycle at these checkpoints until the proper signals are received are called checkpoints.
They ensure that the cell is ready to proceed to the next phase only when certain conditions are met.