CFM 2: Cell Cycle

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CFM 2: Cell Cycle
2015-09-10 12:12:13
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  1. Most cells are in which phase of the cell cycle?
  2. Difference between G1 phase, G0 phase, and post-mitotic cells?
    • G1: average dividing cells
    • G0: quiescent cells (not dividing, but can be stimulated to enter cell cycle)
    • Post-mitotic: incapable of cell division (e.g. mature neurons)
  3. Where in the cell cycle is the R checkpoint?
    Just before G1/S checkpoint
  4. What is the main purpose of the R point in human cell cycle?
    • Checks growth conditions
    • Before R point, checking for sufficient growth factors
    • After R point, growth factors do not matter; the cell is committed to replicating
  5. What happens if a cell does not receive enough growth factors before the R point?
    Stays in G0 phase
  6. CDKs are (active/inactive) on their own
  7. CDKs are activated by ______
  8. 2 different ways p53 acts as a tumor suppressor and protects us from cancer?
    • Induces apoptosis
    • Stops cell cycle by inducing transcription of p21, which is a Cdk inhibitor protein
  9. p21
    Cdk inhibitor protein; transcription induced by p53
  10. p53/p21 pathway in stopping cell cycle
    • DNA damage to UV rays
    • ATM/ATR repair pathway activated
    • Ultimately activating p53
    • p53 induces p21 transcription
    • p21 inhibits G1/S-Cdk and S-Cdk
  11. Wee1
    Phosphorylates CDK1 to inhibit CDK1 activity during S phase
  12. Cdc25
    Phosphatase that dephosphorylates Cdk1 to allow progression from G2 to M
  13. G1 (R point) cyclin and Cdk
    • Cyclin D
    • Cdk4, Cdk6
  14. G1/S cyclin and Cdk
    • Cyclin E
    • Cdk2
  15. S cyclin and Cdk
    • Cyclin A
    • Cdk2, Cdk1**
  16. G2/M cyclin and Cdk
    • Cyclin B
    • Cdk1
  17. Wnt pathway
    Wnt inhibits APC inhibits B-catenin stimulates cyclin D transcription
  18. Rb and its effects on cell cycle
    • Rb binds and inhibits E2F, a transcription factor that stimulates transcription of Cyclin E
    • E2F is activated when Cyclin D-Cdk4 phosphorylates Rb, releasing E2F
  19. How does Cyclin D activation lead to Cyclin E activation?
    • Cyclin D phosphorylates Rb, releasing E2F (to which unphosphorylated Rb is bound and inhibiting)
    • E2F promotes transcription of Cyclin E
  20. How do cyclins/CDKs ensure just one round of DNA replication per cell cycle? Which cyclin/CDK complex does this?
    Cyclin E/Cdk2 phosphorylates pre-replicative complexes on DNA when cells enter S phase, degrading them
  21. Two major ubiquitin ligase complexes in cell cycle control
    • APC (anaphase promoting complex)
    • SCF complex
  22. SCF complex
    • Kind of ubiquitin ligase
    • Has F-box, which is interchangeable and specific to target proteins
    • F-boxes mostly interact with phosphorylated proteins to degrade them; many of the targets are phosphorylated by cyclin/CDKs, which allows substrates to be degraded during specific phases of the cell cycle
  23. 2 functions of Anaphase Promoting Complex (APC)
    • 1. ubiquitin ligase that ubiquitinates Cyclin B (G2/M cyclin)
    • 2. Allow chromosome segregation by ubiquitinating securin (which inhibits separase), activating separase, which unglues cohesin complexes allowing chromosomes to separate