Cell Division

Stimulants• DNA overload• Exchange of material- ratio of

surface area to volume

Cell Cycle Regulators• Cyclins: proteins that regulate the

timing of the cell cycle in eukaryotic cells

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

External Regulators• Respond to events outside the cell• Direct cells to speed up or slow down cycle

ex: growth factors- most importantduring embryonic development and

wound healingex: neighboring cells’ surface molecules slow down cycles (prevents excessive growth & disruption to other tissues)

Proto-oncogenes

• Code for regulatory proteins• Mutation: Oncogene (causes uncontrolled

cell proliferation)

Tumor-suppressor Genes

• Code for proteins that prevent cell division• Mutations – cause cancer

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

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)