1. Cell Division Stimulants DNA overload Exchange of material- ratio of surface area to volume

2. Cell Cycle Regulators Cyclins: proteins that regulate the timing of the cell cycle in eukaryotic cells

3. Internal Regulators Respond to events inside the cell -ex: stops cell from entering mitosis until all chromosomes are replicated -ex: prevents anaphase until all chromosomes are attached to spindles

4. External Regulators Respond to events outside the cell Direct cells to speed up or slow down cycle ex: growth factors- most important during embryonic development and wound healing ex: neighboring cells’ surface molecules slow down cycles (prevents excessive growth & disruption to other tissues)

5. Proto-oncogenes Code for regulatory proteins Mutation: Oncogene (causes uncontrolled cell proliferation)

6. Tumor-suppressor Genes Code for proteins that prevent cell division Mutations – cause cancer

7. Cancer Uncontrolled cell division Form tumors – mass of cells – Benign- remain in mass (Can compress vital organs) – Malignant- invade tissues Results from mutations Chromosomes in cancer cells are unstable– rearrangements, duplications, deletions

8. Cancer Cells lose ability to control growth Causes: smoking, radiation, viruses, chemicals Can metastasize- break off & travel through body- Don’t recognize that they are not attached Defect in gene p53 (halts cell cycle until all chromosomes properly replicated)