Cyclin and CDK in cell cycle progression | How Cyclin CDK works?

Summary

This video explains the pivotal roles of cyclins and cyclin-dependent kinases (CDKs) in regulating the cell cycle. Cyclins fluctuate in synthesis and degradation, partnering with CDKs to phosphorylate target proteins critical for cell cycle progression. Key complexes discussed include Cyclin D/CDK4 in the G1 phase, which helps cells decide to divide; Cyclin E/CDK2 in the S phase, ensuring DNA replication occurs once; and Cyclin B/CDK1 in the M phase, facilitating mitosis. The video highlights the importance of these proteins in maintaining cellular integrity and their implications in cancer biology.

Takeaways

• 🔍 Cyclins are proteins that regulate the cell cycle through a cyclical pattern of synthesis and degradation.
• 🔑 CDKs (Cyclin-Dependent Kinases) require cyclins to be active, functioning together as crucial regulatory units.
• 📈 Cyclin D and CDK4/6 are key players in the G1 phase, activated by growth factors to decide cell division.
• ⚖️ The restriction point in G1 is critical, where cyclin D/CDK4 assesses growth signals and nutrient availability.
• 🛡️ pRB is a tumor suppressor that inhibits E2F, a transcription factor necessary for progression to the S phase.
• 🔄 Cyclin E and CDK2 function in the S phase, ensuring that DNA replication occurs only once per cell cycle.
• 📜 The replication bubble forms through the phosphorylation of licensing proteins by the cyclin E/CDK2 complex.
• 🚀 Cyclin B and CDK1 are essential for the M phase, promoting chromosome condensation and nuclear envelope breakdown.
• ⚠️ p53 plays a vital role in halting the cell cycle in response to DNA damage, allowing for repair or leading to apoptosis.
• 🧬 The balance between cyclins, CDKs, and tumor suppressors is crucial for maintaining genomic stability and preventing cancer.

Q & A

What are cyclins and how are they characterized?

Cyclins are proteins that exhibit a cyclical pattern of synthesis and degradation, meaning their levels rise and fall in a coordinated manner throughout the cell cycle.

What role do cyclin-dependent kinases (CDKs) play in the cell cycle?

CDKs are enzymes that require binding to cyclins to become active. They phosphorylate target proteins to regulate various events in the cell cycle.

Which cyclin-CDK complex is most active during the G1 phase?

The cyclin D and CDK4/6 complex is the most active during the G1 phase.

How does the cyclin D-CDK4/6 complex influence the decision to progress past the restriction point?

This complex assesses growth factor signaling, nutrient availability, and stress factors to decide whether the cell should proceed past the restriction point and divide.

What is the role of the retinoblastoma protein (Rb) in cell cycle regulation?

Rb is a tumor suppressor that inhibits the E2F transcription factor. When phosphorylated by cyclin D-CDK4/6, Rb releases E2F, allowing the cell to progress to the S phase.

What is the function of p53 in the cell cycle?

p53 is a tumor suppressor protein that can pause the cell cycle in response to DNA damage, allowing time for repair or triggering apoptosis if the damage is irreparable.

Which cyclin-CDK complex is active during the S phase and what is its function?

The cyclin E-CDK2 complex is active during the S phase, facilitating the initiation of DNA replication by phosphorylating key regulatory proteins.

How does the cyclin E-CDK2 complex prevent re-replication of DNA?

By phosphorylating components like Cdt1 and Cdc6, the cyclin E-CDK2 complex ensures that replication can only occur once per cell cycle.

What happens to cyclin B-CDK1 after its role in the M phase is completed?

Cyclin B-CDK1 is targeted for degradation through polyubiquitination, which leads to its destruction by the proteasome.

How do cyclin B and CDK1 contribute to the M phase processes?

Cyclin B-CDK1 is essential for events like nuclear envelope breakdown, chromosome condensation, and spindle apparatus formation during the M phase.