1. 5.3 Regulation of the Cell Cycle KEY CONCEPT Cell cycle regulation is necessary for healthy growth.

2. 5.3 Regulation of the Cell Cycle Internal and external factors regulate cell division. External factors include physical and chemical signals. –Come from outside the cell Growth factors are proteins that stimulate cell division. –Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells. –Bind to receptors to activate specific genes to trigger cell growth

3. 5.3 Regulation of the Cell Cycle Internal factors come from inside the cell Two of the most important internal factors are kinases and cyclins. –Kinase: enzyme that transfers a phosphate group from one molecule to a specific target molecule -Are almost always present in a cell –Cyclins: a group of proteins that are rapidly made and destroyed at certain points in the cell cycle -Control kinases External factors trigger internal factors, which affect the cell cycle.

4. 5.3 Regulation of the Cell Cycle –a normal feature of healthy organisms –caused by a cell’s production of self-destructive enzymes –occurs in development of infants –Nucleus in developing cells shrink and break apart –Specialized immune system cells phagocytize them webbed fingers Apoptosis is programmed cell death.

5. 5.3 Regulation of the Cell Cycle Cell division is uncontrolled in cancer. Cancer cells form disorganized clumps called tumors. cancer cell bloodstream normal cell –Benign tumors remain clustered and can be removed. –Malignant tumors metastasize, or break away, and can form more tumors.

6. 5.3 Regulation of the Cell Cycle Cancer cells do not carry out necessary functions. Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.

7. 5.3 Regulation of the Cell Cycle Carcinogens are substances known to promote cancer. Standard cancer treatments typically kill both cancerous and healthy cells.