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Ch. 17 - Cell Cycle Part 1 A summary of the chapter and lecture notes on the cell cycle, part 1. Includes illustrations and graphics from the textbook.

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York University
BIOL 2021
Julie Clark

1 BIOL 2021- April 30 2009 CELL CYCLE- CHAPTER 17 - All cells come from pre existing cells - Cell cycle = cycle of a cell growth and division - Replicate chromosomes and segregate to daughter cells - Organelles replicate and segregate - Increase in mass coordinator with division - S phase and M phase are the most important Major Events in cell cycle - S phase: DNA synthesis (chromosome duplication) - M phase: chromosome segregation and cell division (mitosis and cytokinesis) 1 4 phases - GAP= G1 + G2 Page 2 - When cells are taking time for growing and monitoring environment to assess whether conditions are favourable for growth - Cell cycle: GI->S->G2->mitosis->G1 - Cells can have a G0 phase which is a resting phase  Exit from G1 to G0 - End of G1 there is a START PHASE  Commit to divide  Irreversible (can’t go back, must continue in the cycle) - Cell cycle: a) G1+S+G2= INTERPHASE b) MITOSIS STAGES OF MITOSIS -> Pannel 17.1 1) Prophase - DNA is already replicated - Sister chromatids condense 2) Prometaphase - Chromosomes start to attach to spindle - Nuclear membrane begins to breakdown in animal cells 3) Metaphase 4) Anaphase 5) Telophase - Daughter chromosomes are at poles - Nuclear envelop 6) Cytokinesis - Contractile ring contracts creating cleavage Principles of cell cycle control - Principles are similar in all eukaryotes - Yeast mutants defective in genes for cell cycle  I.e. Cdc gene mutant Control of cycle:  CHECKPOINTS 2 Page 3 1) START= enter cell cycle (point of no return)  Is environment favourable? 2) G2/M: entry into mitosis  Looks to see if DNA synthesis is complete  Looks to see if environment is favourable 3) Metaphase/anaphase transition  Are chromosomes attached to spindle  Spindle attachment checkpoint - Checks are biochemical switches  Initiate events  Block progress if there’s a problem - Many of the steps are controlled by CYCLIN DEPENDANT KINASE (CDK) 3  Never active without cyclin protein Page 4  Cyclical changes in activity of CDKs which drives many events of cell cycle  Phosphorylates proteins  Cyclin is a protein that activates CDKs  Cyclical changes in cyclin levels which CAUSES changes in level of CDK activity  Each cyclin (+ complex)- CDK phosphorylates different substrates CLASSES OF CYCLINS/CDK COMPLEXES 1) G2-CDK  Controls activity of G1/S CDK  Not in all cells 2) G1/S-CDK - Triggers start- cell cycle entry 3) S-CDK  Stimulates chromosome duplication  Also involved in M phase 4) M-CDK  Controls entry into mitosis - Activity of each complex coincides with cyclin levels ACTIVATION/INHIBITION OF CDKS 4 - Phosphorylation events by kinases  CDK activating kinase (CAK) activates CDKs
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