Final answer:
True. The catalytic subunits of the complexes are known as CDKs. CDKs are protein kinases that, when fully activated, phosphorylate and activate other proteins involved in advancing the cell cycle.
Step-by-step explanation:
True. Cyclin-dependent kinases (CDKs) are protein kinases that, when fully activated, can phosphorylate and activate other proteins that advance the cell cycle past a checkpoint. To become fully activated, a CDK must bind to a cyclin protein and then be phosphorylated by another kinase.
This process involves the formation of a Cdk/cyclin complex, where cyclins tightly bind to Cdks. This complex must also be phosphorylated in specific locations to activate the complex. The Cdks, as enzymes, phosphorylate other proteins involved in advancing the cell to the next phase. The levels of Cdk proteins remain relatively stable throughout the cell cycle, while the concentrations of cyclin fluctuate and determine when Cdk/cyclin complexes form at specific points in the cell cycle, regulating different checkpoints.