BS 161 1st Edition Lecture 26 Outline of Last Lecture I Cell cycle I Outline of Current Lecture II Cell cycle II Current Lecture cell cycle clock engine a series of activation and deactivation reactions of proteins cyclins and cyclin dependent kinases that pace the cell cycle G1 start determine if DNA synthesis should begin G2 determine if mitosis should begin M determine if mitosis should be completed cytoplasmic factors control nuclear events the start G1 phase is dominated by the M phase in experiments where the cells are fused together the chromosome of the G1 cell condenses cyclins regulate transcription and translation cyclins are proteins they build up during interphase and reach their peak at mitosis cyclins bind to and activate kinase mitosis promotion factor MPF is made of cyclin and cyclin dependent kinase CDK MDF functions nuclear lamins phosphorylated chromosome condensation and spindle formation some proteins can inhibit MDF one is called P27 it inhibits the cell cycle by making the MPF not functional P27 inhibits the inhibitor of the cell cycle mice with P27 are larger than mice without major phenotypic changes in cancer cells 1 loss of checkpoint controls 2 immortality cancer cells can continually divide 3 loss of adhesion dependence and gain of motility cancer cells form overlapping layer of rounded cells
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