Final answer:
The cell-cycle control system utilizes checkpoint activation to control the cellular machinery, ensuring the cell is ready for each phase and rectifying any issues before continuing, which is critical for preventing uncontrolled cell division.
Step-by-step explanation:
The cell-cycle control system controls machinery through D. Checkpoint activation. This involves various regulatory proteins signaling the cell to start or delay the next phase of the cycle, ensuring the cell is ready before moving on.
Checkpoints are crucial in the cell cycle, acting as quality control points where the cycle can be halted to assess and rectify any issues before proceeding. At the G1 checkpoint, the integrity of the DNA is assessed. At the G2 checkpoint, proper chromosome duplication is verified. Finally, the M checkpoint evaluates the attachment of each kinetochore to a spindle fiber during metaphase.
Regulatory molecules like cyclins and cyclin-dependent kinases (Cdks) serve as positive regulators to advance the cell cycle, while negative regulators, such as tumor suppressor proteins, monitor conditions and can pause the cycle if necessary. These mechanisms are essential in preventing conditions such as cancer, which is characterized by uncontrolled cell division.