BIOL 2021 Chapter Notes - Chapter 17.1: E2F, Cell Division, P53
11 Feb 2018
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In unicellular organisms (ex. yeast), the signal is nutrients: divide as fast as possible. Multicellular organisms use specific signals called mitogens. Mitogens: extracellular signals that are secreted by other cells. Mitogens all act in g1 phase and activate cdks. Mitogens interact with cell surface receptors, activates ras, which causes a map kinase cascade to stimulate gene regulation. Myc (gene regulatory protein) gets activated: immediate early . Myc causes g1 cyclin expression and g1-cdk is activated. G1-cdk phosphorylates rb (retinoblastoma), which becomes inactive and releases its bound e2f: rb inactivates e2f when it is active by binding to it. E2f: gene regulatory protein that stimulates genes for g1/s cyclins, s cyclins, and other proteins for dna synthesis. A positive feedback loops keep e2f active. G1 and g1/s cyclins resistant to apc. Can sometimes exit to g1 with the right signals. The dna damage checkpoint is present in late g1 (start) and g2/m.
