C ONTROL OF C ELL D IVISION : M ITOSIS G ONE W RONG Mrs. Stewart Central Magnet School Honors Biology

W HAT TRIGGERS A CELL TO BEGIN MITOSIS ? Proteins regulate the progress of cell division A system of checkpoints occurs Certain feedback signals from the cell can trigger the proteins to initiate the next phase of the cell cycle

3 CHECKPOINTS FOR M ITOSIS G1 – cell growth checkpoint G2 – DNA synthesis checkpoint Mitosis checkpoint

G 1 – CELL GROWTH CHECKPOINT If the cell is healthy and the cell has grown to a suitable size  proteins initiate S phase (DNA replication) If DNA replication is not favorable in the cell’s current condition/environment, cell cycle stops here (G 0 ) Or if cell needs rest (G 0 ) ** Cells that enter G 0 will likely never divide again

G2 – DNA SYNTHESIS CHECKPOINT After DNA has replicated itself DNA repair enzymes are triggered to check the results of DNA replication for errors If this checkpoint is passed, proteins signal the cell to begin mitosis

M ITOSIS CHECKPOINT If a cell passes this checkpoint, proteins signal the cell to exit mitosis and enter G 1 phases once again

T HINK – P AIR – S HARE What could be a complication of cells dividing too many times / too rapidly?

W HEN CONTROL IS LOST : The proteins that control the process of cell division are coded for by genes If there is a mutation, those proteins are created incorrectly If a protein is shaped wrong, it cannot function correctly  uncontrolled cell growth

C ANCER Tumors - a collection of cells dividing out of control They require more resources than surrounding cells because they are more active Starve all surrounding cells Can break off and travel through bloodstream to spread