Progression through the cell cycle is regulated by oscillations in the concentration of which types of molecule?

Options

A. Actin
B. Tubulin
C. Cyclin - dependent kinases
D. Cyclines

Answer

To answer the question regarding the regulation of progression through the cell cycle, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Progression through these phases is tightly regulated to ensure proper cell division.

2. **Role of Checkpoints**: There are specific checkpoints in the cell cycle (G1 to S, G2 to M, and M phase) that monitor the cell's readiness to proceed to the next phase. These checkpoints are critical for maintaining the integrity of the cell division process.

3. **Key Regulatory Molecules**: The progression through the cell cycle is regulated by two main types of molecules: cyclins and cyclin-dependent kinases (CDKs).

4. **Cyclins**: Cyclins are proteins whose levels fluctuate throughout the cell cycle. They are synthesized and degraded in a cyclical manner, hence the name "cyclins." Their concentration peaks at specific points in the cell cycle.

5. **Cyclin-Dependent Kinases (CDKs)**: CDKs are enzymes that, when activated by binding to cyclins, phosphorylate target proteins to drive the cell cycle forward. The activity of CDKs is dependent on the presence of their corresponding cyclins.

6. **Oscillation of Concentrations**: The oscillation in the concentration of cyclins leads to the activation of CDKs at various points in the cell cycle. For example, cyclin D binds to CDK4/6 to help the cell transition from G1 to S phase, while cyclin B activates CDK1 to facilitate the transition from G2 to M phase.

7. **Conclusion**: Therefore, the progression through the cell cycle is regulated by oscillations in the concentration of cyclins and the activity of cyclin-dependent kinases (CDKs).

### Final Answer:
Progression through the cell cycle is regulated by oscillations in the concentration of cyclins and cyclin-dependent kinases (CDKs).

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