Final answer:
Cells move past the G2 transition point and into mitosis through the activation of cdc2 by mitotic cyclins. Mitotic cyclins bind to Cdk to form MPF, which phosphorylates other proteins to advance the cell cycle.
Step-by-step explanation:
Movement past the transition point near the end of G2 that moves cells on to mitosis requires cdc2 activation by mitotic cyclins. The G2 checkpoint is a crucial part of the cell cycle where cells prepare for mitosis. It is at this point that cyclin-dependent kinases (Cdks) play a vital role. Cdks, when fully activated, can phosphorylate other proteins to advance the cell cycle past the checkpoint. For full Cdk activation, binding to a cyclin protein is necessary, which then allows further phosphorylation by another kinase.
Mitotic cyclins accumulate during interphase and bind to Cdk subunits. This binding is a critical step in the cell's transition to mitosis as it forms a complex known as maturation-promoting factor (MPF). MPF's kinase activity, which requires mitotic cyclins, peaks at the end of G2, triggering entry into mitosis. Thus, mitotic cyclins are essential for Cdc2 activation, which allows cells to pass through the G2/M transition.