1. Cell Cycle Kinases The cell cycle refers to the process from the end of cell division to the end of the next cell division. DNA synthesis and cell division are the two major events in the cell cycle. In the process of evolution, cells develop and establish a series of regulatory mechanisms to ensure that the cell cycle phases are strictly ordered. The molecules that have been found to be involved in cell cycle regulation can be divided into three broad categories: cyclin, cyclin kinase/phosphatase, cyclin-dependent kinase inhibitor (CKI), and cyclin-dependent protein kinase, which belongs to the serine/threonine protein kinase family. CDK drives the cell cycle through the chemical action of serine/threonine protein, and synergizes with the cyclin, which is an important factor in cell cycle regulation. CDK can form a heterodimer with cyclin, in which CDK is a catalytic subunit, and cyclin is a regulatory subunit, and different cyclin-CDK complexes catalyze the phosphorylation of different substrates through CDK activity, thereby achieving different cell cycle times. The activity of CDK is dependent on the sequential expression of its positive regulatory subunit cyclin and its concentration of negative regulatory subunit CKI (cyclin-dependent kinase inhibitor, CDK inhibitor). At the same time, CDK activity is also regulated by phosphorylation and dephosphorylation. CyclinB generally begins to synthesize in the late G1.