AP Biology The Cell Cycle

Checkpoints (Is all going according to plan?)

Relative concentration . M G1 S G2 M G1 S G2 M MPF activity Cyclin Relative concentration Time Fluctuation of MPF activity and cyclin concentration during the cell cycle

Molecular mechanisms that help regulate the cell cycle . G1 Cyclin S Cdk Degraded cyclin M G2 accumulation G2 checkpoint Cdk Cyclin is degraded Cyclin MPF Molecular mechanisms that help regulate the cell cycle

Chromosome movement Kinetochore Tubulin subunits Motor Microtubule . Chromosome movement Kinetochore Tubulin subunits Motor protein Microtubule Chromosome

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). 25 µm Normal mammalian cells

Cancer cells do not exhibit anchorage dependence . 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 Cell cycle-stimulating pathway NUCLEUS Growth factor MUTATION 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 MUTATION Defective or missing transcription factor, such as p53, cannot activate Active form of p53 UV light DNA damage in genome DNA Protein that inhibits the cell cycle