Final answer:
Cells have three checkpoints in the cell cycle: near the end of G1, at the G2/M transition, and during metaphase, regulated by molecules like cyclins and Cdks, which act as positive regulators, and tumor suppressor proteins, which serve as negative regulators to prevent errors.
Step-by-step explanation:
Cells control the cell cycle by integrating internal information and external signals and delaying (or even halting) the cell cycle at three checkpoints. These checkpoints ensure that cells do not proceed to the next stage of division until all necessary conditions are favorable and accurate duplication of chromosomes is guaranteed.
The checkpoints are strategically located at various points in the cycle: near the end of G₁, at the G₂/M transition, and during metaphase. Molecules such as cyclins and cyclin-dependent kinases (Cdks) play key roles in regulating these checkpoints.
Positive regulators such as these allow the cell to proceed with division, while negative regulators, including tumor suppressor proteins, can halt the cycle to prevent errors that may lead to conditions like cancer, characterized by uncontrolled cell division.
These checkpoints occur near the end of G₁, at the G₂/M transition, and during metaphase. Positive regulator molecules, such as cyclins and cyclin-dependent kinases (Cdks), allow the cell cycle to advance to the next stage, while negative regulator molecules, like tumor suppressor proteins, monitor cellular conditions and can stop the cycle until specific requirements are met.