What are CDKs? What role do they play in the cell cycle?

CDKs (cyclin dependent kinases) are crucial regulatory enzymes involved in cell proliferation through regulating cell-cycle checkpoints and transcription in response to intracellular and extracellular cues. CDKs phosphorylate their substrates by transferring phosphate groups from ATP to specific regions of amino acids in the substrates. Different types of eukaryotic cells possess different types and numbers of CDKs. For example, yeasts only contain a single CDK, while in contrast, vertebrates have four different ones. As its name suggests, CDKs require the presence of cyclins to become activated. All eukaryotes have multiple cyclins which act during a specific stage of the cell cycle. Each CDK is paired with a specific cyclin in organisms with multiple CDKs.