Cell cycle basics

 

  • Growth factors in circulation interact with the GF receptors on cells.
  • Growth suppressors antagonize the action of growth factors.
  • Eventually GFs will stimulate sufficiently to overcome suppression
  • GFs open ion gated channels, activate protein kinases directly or act via secondary messengers.
  • This leads to the production of G1 Cyclins inside the cell.
  • G1 Cyclins bind to CDKs
  • These promote passage of cell past the G1 restriction point into S phase.
  • EventuallyGg1 cyclins decrease
  • G1/S cyclins are produced
  • These bind to CDKs and commit the cell to DNA replication
  • G1/S cyclin levels decrease
  • S cyclins are produced
  • These bind to CDKs and promote DNA replication
  • The amount of DNA in the nucleus doubles.
  • S cyclins decrease
  • M cyclins are produced in late S phase.
  • These bind to CDKs but are initially inactive due to phosphorylation by Wee1 a kinase
  • When cdc25, a phosphatase, is activated, it removes the P group from the M-CDks activating them
  • This triggers mitosis and cytokinesis.
  • Eventually M cyclins decrease and the 2 cells end up in G0 again.

 

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