The passage of a cell through the stages of the cell cycle is controlled by protein kinases that phosphorylate many different proteins at appropriate times. What are these protein kinases called?

Options

A. Cdk activating kinases
B. Cyclin-dependent kinases
C. Cyclins
D. Tyrosine kinases

Answer

To answer the question regarding the protein kinases that control the passage of a cell through the stages of the cell cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of several stages, including G1, S, G2, and M phases. Each phase is crucial for cell growth and division.

2. **Role of Protein Kinases**: Protein kinases are enzymes that add phosphate groups to proteins (phosphorylation), which can activate or deactivate the target proteins, thereby regulating various cellular processes.

3. **Checkpoints in the Cell Cycle**: The cell cycle has specific checkpoints, such as the G1 checkpoint, where the cell assesses whether it is ready to proceed to the next phase (S phase).

4. **Cyclins and Cyclin-Dependent Kinases (CDKs)**: The activity of protein kinases in the cell cycle is regulated by proteins called cyclins. When cyclins bind to specific protein kinases, they form a complex known as Cyclin-Dependent Kinase (CDK) complexes.

5. **Function of CDK Complexes**: These CDK complexes are essential for the progression of the cell cycle. They phosphorylate target proteins that are necessary for the cell to move from one phase to the next.

6. **Conclusion**: The protein kinases that control the cell cycle are referred to as Cyclin-Dependent Kinases (CDKs).

### Final Answer:
The protein kinases that control the passage of a cell through the stages of the cell cycle are called **Cyclin-Dependent Kinases (CDKs)**.

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