Final answer:
The cell division cycle is controlled by regulatory proteins such as cyclins and cyclin-dependent kinases (Cdks). These proteins ensure that the events of the cell division cycle occur in the same sequence. Positive and negative regulator molecules play a role in advancing or halting the cell cycle as needed.
Step-by-step explanation:
The cell division cycle is controlled by a number of regulatory proteins that ensure the events of the cell division cycle always occur in the same sequence. These regulatory proteins include cyclins and cyclin-dependent kinases (Cdks), which act as internal molecular signals to regulate cell transitions through the various checkpoints of the cell cycle. Positive regulator molecules like cyclins and Cdks allow the cell cycle to advance to the next stage, while negative regulator molecules like tumor suppressor proteins monitor cellular conditions and can halt the cycle until specific requirements are met.