Podcast
Questions and Answers
How does the binding of a cyclin to a CDK activate the CDK?
How does the binding of a cyclin to a CDK activate the CDK?
- By increasing the rate of translation of the CDK mRNA
- By increasing the rate of transcription of the CDK gene
- By stabilizing the CDK protein and preventing its degradation
- By changing the conformation of the CDK and exposing its active site (correct)
Which cyclin peaks during the G1 phase of the cell cycle?
Which cyclin peaks during the G1 phase of the cell cycle?
- Cyclin D (correct)
- Cyclin A
- Cyclin E
- Cyclin B
Which enzyme is responsible for inactivating CDKs by phosphorylation?
Which enzyme is responsible for inactivating CDKs by phosphorylation?
- Cdc25 phosphatase
- Protein kinase A
- Protein kinase C
- Wee1 kinase (correct)
What is the role of CDK inhibitors (CKIs) in the regulation of the cell cycle?
What is the role of CDK inhibitors (CKIs) in the regulation of the cell cycle?
How does phosphorylation by a CDK affect its target protein?
How does phosphorylation by a CDK affect its target protein?
What happens to cyclin levels during the cell cycle?
What happens to cyclin levels during the cell cycle?
Which cyclin peaks during the S phase of the cell cycle?
Which cyclin peaks during the S phase of the cell cycle?
What is the function of Cdc25 phosphatase in the regulation of CDKs?
What is the function of Cdc25 phosphatase in the regulation of CDKs?
Which cyclin peaks during the G2 phase of the cell cycle?
Which cyclin peaks during the G2 phase of the cell cycle?
Which enzyme is responsible for activating CDKs by dephosphorylation?
Which enzyme is responsible for activating CDKs by dephosphorylation?
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Study Notes
Cyclin-CDK Complexes
- Essential for controlling the cell cycle, comprising a cyclin and a cyclin-dependent kinase (CDK)
- Activity is tightly regulated to ensure proper cell cycle progression
Cyclin Synthesis and Degradation
- Cyclins are synthesized and degraded in a precise pattern during the cell cycle
- Levels fluctuate, with each type peaking at different stages to promote specific cell cycle events
- Example: cyclin D peaks during G1, cyclin E during G1/S transition, cyclin A during S and G2, and cyclin B during M phase
CDK Activation
- CDKs are activated by binding of a cyclin
- Binding changes CDK conformation, exposing its active site and allowing phosphorylation of target proteins
- Phosphorylation can either activate or inactivate target proteins, leading to cell cycle progression
CDK Inhibitors (CKIs)
- Proteins that bind to cyclin-CDK complexes and inhibit their activity
- Serve as a checkpoint mechanism to prevent cell cycle progression under conditions like DNA damage or incomplete replication
Phosphorylation Regulation
- CDKs are regulated by phosphorylation
- Inactivated by phosphorylation at specific sites by Wee1 kinase
- Activated by dephosphorylation by Cdc25 phosphatase
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