Term
Stages of the cell cycle in sequence? |
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Definition
G1: growth of cell esp of enzymes required in dna synthesis. restriction point & commitment!
S: DNA replication & synthesis
G2: cytoplasmic expansion. incr synthesis of things needed for mitosis e.g. microtubules.
M: mitosis, characterized by karyokinesis (/ of DNA) and cytokineses (/ of cytoplasm & organelles) |
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Term
Why have checkpoints in the cell cycle? |
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Definition
To prevent damaged DNA from being replicated and passed down to daughter cells. |
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Term
What regulates the cell cycle? |
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Definition
CDK-cyclin complexes. I.e. the presence of CDK, which is dependent on the presence of cyclins. |
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Term
Which are the CDKs/Cyclins that drive a cell through the G1 phase? |
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Definition
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Term
What is the CDK/cyclin complex that drives a cell through the rate limiting step at the end of G1? |
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Definition
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Term
Describe how CDKs are activated. |
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Definition
CDK is phosphorylated in 3 points - threonine 14, tyrosine 15 and threonine 160. When a phosphatase comes along and 2 phosphate groups are taken off (threonine 14 and tyrosine 15), the CDK complex becomes active. Mitosis then occurs! |
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Term
What are the 3 factors that regulate CDK levels? |
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Definition
1. Association with Cyclins
This in turn is affected by presence of growth factors that enhance the transcription of certain cyclins.
2. Activating/Inhibitory Phosphorylation
Require initial priming of the complex by phosphorylation @ 3 sites by a kinase. Then a phosphatase needs to come along and knock phosphate groups off the threonine 14 & tyr 15.
3. Presence of CKI's
Self explanatory! |
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Term
What is p53 and what role does it play in the cell cycle? |
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Definition
| p53 is a protein that acts as a transcription factor, scanning for damage in DNA before it passes through the G1 checkpoint. If damage is spotted, [p53] rises. p53 then has a 2fold action: spots DNA damage (proofreading) and enhances the transcription of a gene coding for p21. |
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Term
What is p21 and what role(s) does it play in the cell cycle? |
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Definition
p21 is a protein that has 3 main functions
- Inhibits the action of CDKs therefore prevents the cell from entering S phase
- Binds to DNA pol hence DNA is not synthesized
- Induces apoptosis
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Term
Growth factors mediate their action (which is what???) through _______ __________. |
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Definition
Growth factors switch on the transcription and translation of cyclins. They mediate their actions through 2nd messengers. |
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Term
What are the points in DNA where DNA replication occurs? |
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Definition
ORCs (Origin Recognition Complexes) |
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Term
How is the S phase regulated? |
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Definition
Late G1 Cyclin CDC6 binds to the ORC. This binding recruits helicases (MCMs) to form a polymerization complex around the ORC. Transition to S phase helicases unravel dsDNA at these ORCs & allow DNA pol to bind. S phase CDKs phosphorylate the CDC6 & cause its degradation. DNApol can now bind & replicate DNA!
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