Final answer:
Checkpoints are important in the cell cycle control system as they determine whether the cell can continue to the next phase or should be halted. There are three main checkpoints: G1, G2/M transition, and metaphase. At each checkpoint, different molecules act as stop-or-go signals depending on the cell's conditions.
Step-by-step explanation:
Checkpoints play a crucial role in the cell cycle control system. These checkpoints are points in the cell cycle at which the cycle can be signaled to move forward or halted. There are three main checkpoints in the cell cycle: the G1 checkpoint, the G2/M transition checkpoint, and the metaphase checkpoint.
At each checkpoint, different molecules act as stop or go signals, depending on the conditions within the cell. For example, at the G1 checkpoint, the cell must be ready for DNA synthesis to occur. If the conditions are not favorable, the cell cycle progression will be halted until the conditions improve.