Final answer:
A) Cyclin rises during G2, but aren't activated until the end of G2
Step-by-step explanation:
During the G2 phase of the cell cycle, the concentration of A) Cyclin rises, preparing the cell for the subsequent phase, which is mitosis. Cyclins are regulatory proteins that, when bound to cyclin-dependent kinases (CDKs), activate them. However, their activation occurs at the end of G2 and is a critical event that triggers the cell to enter mitosis. Cyclin-CDK complexes play a key role in regulating the cell cycle by controlling transitions between different phases.
In the G2 phase, cells undergo final preparations for cell division. Cyclins are synthesized during this phase, and their levels gradually increase. However, the activation of Cyclin-CDK complexes, including Cyclin B-CDK1, is delayed until the end of G2. This delay ensures that the cell has completed necessary processes, such as DNA replication and repair, before entering mitosis. The activation of Cyclin-CDK complexes at the G2/M checkpoint is a crucial regulatory step that ensures the fidelity of cell division.
In summary, while Cyclin levels rise during G2, their full activation, along with CDKs, is temporally regulated to occur precisely at the end of G2. This tight regulation ensures that the cell progresses through the cell cycle in a coordinated and controlled manner, preventing errors and maintaining genomic integrity.