AP Biology Chapter 12 The Cell Cycle Checkpoints
AP Biology Chapter 12: The Cell Cycle
Checkpoints (Is all going according to plan? )
Relative concentration . M G 1 S G 2 M MPF activity Cyclin Time Fluctuation of MPF activity and cyclin concentration during the cell cycle
G Cdk G 2 checkpoint MPF Cdk ion Cyclin is degraded M Degraded cyclin accumulat Cyc S 1 . Cyclin Molecular mechanisms that help regulate the cell cycle
. Chromosome movement Microtubule Motor protein Chromosome Kinetochore Tubulin subunits
. Cells anchor to dish surface and divide (anchorage dependence). When cells have formed a complete single layer, they stop dividing (density-dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the gap and then stop (density-dependent inhibition). Normal mammalian cells 25 µm
. Cancer cells do not exhibit anchorage dependence or density-dependent inhibition. 25 µm Cancer cells
Malignant cancer cells from the breast (See the ABNORMAL “crab” shape of the cells. )
Mutations and Cancer MUTATION Growth factor Hyperactive Ras protein (product of oncogene) issues signals on its own G protein Cell cycle-stimulating pathway Receptor Protein kinases (phosphorylation cascade) NUCLEUS Transcription factor (activator) DNA Gene expression Protein that stimulates the cell cycle Cell cycle-inhibiting pathway Protein kinases UV light DNA damage in genome Active form of p 53 DNA Protein that inhibits the cell cycle MUTATION Defective or missing transcription factor, such as p 53, cannot activate transcription
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