What are the two types of regulators in the cell cycle?

Cyclins and CDKs are the two types of regulators in the cell cycle. Cyclins regulate the cell cycle exclusively when they are bound to CDKs. In order to be fully activated, the cyclin-CDK complex must be phosphorylated in specific regions. CDKs are enzymes that are responsible for phosphorylating other proteins. These proteins are involved in advancing the cell to the next phase of the cell cycle. The levels of CDK proteins remain stable throughout the cell cycle. However, concentrations of cyclin vary and determine when the cyclin-CDK complexes form. The different cyclins and CDKS bind at specific points during the cell cycle and therefore modulate different checkpoints.