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Cell Cycle Control System . Checkpoints stop the cycle until go-ahead signal is received. There are 3 checkpoints (G 1 , G 2 , & M) that must be passed before Mitosis is completed. . Molecules associated with the cell-cycle clock.

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cell cycle control system
Cell Cycle Control System
  • Checkpoints stop the cycle until go-ahead signal is received.
    • There are 3 checkpoints (G1, G2, & M) that must be passed before Mitosis is completed.
molecules associated with the cell cycle clock
Molecules associated with the cell-cycle clock
  • Cdks - cyclin-dependent kinase (remember that a kinase is an enzyme that activate or inactivate by phosphorylating)
    • cyclin is always present in the cell and is activated when phosphorylated
    • synthesized during the S-phase
  • MPF - M-phase promoting factor
    • partner molecule to Cdk
    • peaks during M phase and initiates Mitosis
    • aids in the disassembly of the nuclear lamina
    • switched off during Anaphase
molecules associated with the cell cycle clock1
Molecules associated with the cell-cycle clock
  • Growth factor
    • secreted by near-by cells
    • called a mitogen
    • many allow the cell to proceed past the G1 checkpoint
      • if the go-ahead signal is not reached it switches to the G0 phase
        • most adult cells are at this position
external controls
External controls
  • density dependent inhibition
    • cells stop dividing when overcrowded
  • anchorage dependence
    • to divide cells must be anchored
cancer
Cancer
  • Cancer cells lack the inhibition pathways
    • are immortal or stop at odd places in the cycle
      • HeLa cell line has been dividing since 1951
      • usually 20-50 replications before cell death
    • normal cells are transformed to cancer cells through a transformation process
    • if the cells stay in the same location they are said to be benign
    • if the tumor invades an organ and impair its function, it is said to be malignant
    • when the cancer cells travel to different locations they are metastatic (process is metastasis)
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