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18 Cards in this Set
- Front
- Back
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What phases in the cell cycle is most variable in duration? What else occurs during these phases?
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G1 (period of time during which cell contents double in amount) and G2
Cells can change minds about proliferating because of check points |
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A cell can do the following to exit the cell cycle. Describe each.
Quiescence Permanent Growth Arrest Programmed Cell Death |
Quiescence: Cell enters G0; is not actively dividing. Can divide when necessary. Ex: hepatocytes
Permanent Growth Arrest: Terminal Differentiation; ex: neurons, cardiac myocytes Programmed Cell Death: Apoptosis |
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What is the function of cyclins?
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Regulate the activity of cyclin-dependent kinases. Binding of cyclin to its cdk partner activates kinase activity of cdk.
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How did cyclins get their name? Provide specific examples.
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Cyclin levels vary throughout the cell cycle; levels are CYCLICAL.
G1: Cyclin D/cdk 4 S: Cyclin E/cdk 2 G2: Cyclin A/cdk 2 M: Cyclin B/cdk 1 |
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What do cyclin dependent kinases do?
What does their activity depend on? |
CDK's are mostly serine/threonine kinases. Very few are tyrosine kinases.
Activities fluctuate dependin on availability of their cyclin partners. |
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What is the role of Cyclin-Dependent Kinase Inhibitors?
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Regulate cell cycle progression
Binding of a CKI to cyclin/CDK complex inhibits CDK activity. |
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What are the two major classes of CDK-inhibitors? When is each active?
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KIP: G1, G2
INK: G1 |
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How does the Cyclin-CDK complex become active? Inactive?
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Cyclin-CDK is activated when Cyclin Activating Kinase (CAK; e.g., Cyc H/CDK 7) phosphorylates it
Becomes inactive when Phosphatase (cdc25) dephosphorylates it |
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What are some of the cell cycle quality control checkpoints?
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Checks whether DNA has been replicated
Checks for DNA damage Checks if cell is big enough for cell division |
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What happens once a cell passes through the restriction point?
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Becomes committed to DNA synthesis and division
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How is the cell cycle restriction point regulated by the activity of retinoblastoma protein?
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Rb binds E2F (transcription factor)
Rb-E2F is INACTIVE Cyc-CDK-Pi phosphorylates Rb-E2F E2F separates and is active Binds DNA, induces transcription of genes necessary for passage through restriction point |
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Why is retinoblastoma protein considered a tumor suppressor?
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Rb sequesters and 'inactivates' E2F, thereby inhibiting progression through the cell cycle.
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What alteration in the cell cycle occurs in breast cancer, leukemia, and testicular carcinomas?
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Gene amplification resulting in overexpression of cyclins D, E
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What alteration in the cell cycle occurs in retinoblastoma, small cell lung carinomas, and osteosarcomas?
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Mutational inactivation of Rb protein
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What alteration in the cell cycle occurs in cervical cancer?
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Sequestration of Rb by HPV E7 protein
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What could a deletion or mutation of CKI genes result in?
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Cancers (including prostate)
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What is the best indicator of cell size?
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Ribosome number
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What is the number of ribosomes in a cell regulated by?
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Their synthesis
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