BSC 422 Lecture Notes - Lecture 8: Cyclin E, Cytokinesis, Ubiquitin
19 May 2018
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Regulation of Cell Growth: Normal Cell Cycle
• DNA synthesis
• Amount of DNA
• Entrance into cell cycle controlled by growth factor requirement
• Subsequent steps usually automated
• 1st checkpoint: S and G1, right before DNA replication (most important)
• 2nd: G2 and M
• 3rd: mitosis and cytokinesis
Cell Cycle
• Interphase
o G1, S and G2
o Once the cell leaves G1, cell is on path committed with a lot of resources
• Mitosis
o Mitosis and cytokinesis
• G0 – permanent cells
o Differentiated into adult state, will never divide again
• Make sure chromosomes have divided equally and properly before cytokinesis
Ability of Cells to Divide
• Variable
o Cells with mitotic activity: epithelial cells
▪ Usually in continually renewing tissues
• Ex. Hair, nails, GI tract, mouth and nose
o Cells in G0 → nerve cells; heart
▪ Normally don’t divide
• Can be induced to undergo DNA synthesis and cell division
• Must receive appropriate signal
o Cells that remain in G0 until death
▪ Lost ability to receive signal
Checkpoints are Molecule Breaks
• Both can be causes of cancer
• G1 checkpoint or START
o Regulates passage into S phase
• G2 checkpoint
o Regulates passage into mitosis
CDKs and Cyclins
• Cyclins – can be degraded. Targets of E3 ubiquitin ligases
o Originally identified because their concentrations went up and down during cell
cycle
o All have core structural similarities but are also different (16 in humans)
• CDKs – cyclin dependent kinases (fairly constant)
o 10 in humans
o Need to bind cyclins to be activated
o Phosphorylate targets
• Different combinations control passage through various checkpoints in cell cycle
• Control
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