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Cell Cycle Checkpoints

Cell Cycle Checkpoints. Checkpoints. They monitor the cell cycle before it can proceed to the next stage. Phosphorylation. The primary molecular mechanism of cell cycle Addition of phosphate group to amino acids Kinases - enzyme that adds phosphate

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Cell Cycle Checkpoints

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  1. Cell Cycle Checkpoints

  2. Checkpoints • They monitor the cell cycle before it can proceed to the next stage

  3. Phosphorylation • The primary molecular mechanism of cell cycle • Addition of phosphate group to amino acids Kinases - enzyme that adds phosphate Phosphatases - enzyme that removes phosphate

  4. How does the phosphorylation of some target proteins control the cell cycle?

  5. How does the phosphorylation of some target proteins control the cell cycle? • Phosphorylation initiates a chain of events that culminates in the activation of certain transcription factors. • These transcription factors promote the transcription of certain genes whose products are required for the next stage of the cell cycle.

  6. cdc Kinases • Enzymes that serves as the checkpoint before each cycle. • They serve as Master Control molecules that works in conjunction with proteins called cyclins.

  7. Cdk Proteins • Cyclin-dependent Kinase Protein • When the cdckinase works in conjunction with the different cyclinsin the cell.

  8. CHECKPOINTS • G1/ S Checkpoint • G2/ M checkpoint • M Checkpoint

  9. G1/ S Checkpoint • Monitors the size that the cell has achieved following the previous mitosis, whether the DNA has been damage . • Decides whether or not to divide Example in Yeast: cdc2 (important kinase in yeast) + S-phase-specific cyclin = G1/S Cdk

  10. P53 Protein • Protein that function during apoptosis or DNA repair • Tumor suppressor gene

  11. G2/ M checkpoint • Physiological conditions in the cell are monitored prior to entering mitosis • Assesses the success of DNA replication Example: MPF

  12. MPF (maturation/mitosis-promoting factors) • Cdk that acts at the G2 checkpoint • Sensitive to agents that disrupt or delay replication and to agents that damage DNA

  13. M/ Spindle Fiber Checkpoint • Ensures that all the chromosomes are attached to the spindle in preparation for anaphase Example: APC

  14. APC (Anaphase Promoting Complex) • Releases protease that destroy cohesin Protease - breaks down protein Cohesin - protein that held together the sister chromatids

  15. Importance of Checkpoints • It assess DNA damage • It function as a clock that will determine how long a phase should take. (Temple and Raff, 1986) • It ensure the fidelity of cell division in eukaryotic cells

  16. Assignment: • Prepare for a Test on Wednesday (1-22-12) • Define the following: • Cancer • Tumor • Metastases • Oncogenes • Tumor Suppressor Genes • Top 10 Causes of Cancer Deaths in the Philippines

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