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 important
during embryonic development and
wound healing
ex: 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)