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Biological Sciences

CELL CYCLE – approx 22 hrs Tightly regulated Basic Requirements: 1. cell size doubles 2. chromosomes replicate 3. MTOC replicates  SPINDLE 4. chromosomes equally distribute 5. cell must divide (cytokinesis) INTERPHASE: G 1 can decide to go quiescent (G )0or move on to S or DIE major decision-making phase: nutrients growth factors signals from other cells G 0 effectively have exited the cell cycle; no longer proliferating S – DNA replication amt of DNA in cell populations can be quantitated by FACS G 2 prepares for mitosis; tetraploid state monitoring step cell enlargement MITOSIS (M) spindle assembles chromosomes condense MT’s disassemble nuclear envelope MT’s grab chromosomes (motors at KINETOCHORE) kinetochore capturing is monitored as a checkpoint cytokinesis waits for full separation **Embryonic Cell Cycle: S and M phases only** Prophase: MTOC separates chromosomes condense Prometa: NE breaks down chromosomes captured (mutlipled MT’s/chromosome) Metaphase: chromo. line at equator Anaphase A: separate chromosomes (DYNEIN (-) motors walk along MT’s) Anaphase B: centrosomes separate (MT’s slide against each other) Telophase: cleave furrow prominent Cytokinesis CELL CYCLE BIOCHEMISTRY Cyclin – Dependent Kinases (CDK’s) drive cell cycle by phosphorylating downstream proteins own cyclin is degraded after next step occurs  cyclin levels rise and fall thoughout cell cycle cyclins activate and help determine CDK substrate specificity their binding enables ATP binding Cyclins destroyed by proteolysis (ubiquitin-directed) Complexes: each composed of different cyclin and different CDK combination G 1DK G 1 S CDK: promotes S phase from G 1 S CDK M CDK
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