What is a characteristic of cyclin-dependent kinases?

Cyclin-dependent kinases (CDKs) are a family of enzymes that play a vital role in regulating the cell cycle. A key characteristic of these enzymes is that they require the presence of cyclins to become active; without cyclins, CDKs remain inactive. Cyclins are regulatory proteins that bind to CDKs, allowing them to phosphorylate specific target proteins, which is crucial for the progression of the cell cycle.

The activation of CDKs through cyclin binding illustrates the importance of this regulatory mechanism in cell cycle control, as it ensures that the cell progresses through different phases at the appropriate times. This relationship underscores how the activity of CDKs is tightly linked to the presence of cyclins, making them dependent on these proteins for functionality.

While some other options, such as the roles related to apoptosis or nutrient uptake, may refer to different proteins or pathways, they do not accurately describe the defining characteristic of CDKs. This emphasizes the unique and essential function of cyclins in regulating CDK activity within the cell cycle.