The Cell Cycle…Gone Wrong

• How do cells know when to divide…• What controls the cell cycle…• Cells grown in a lab will continue to divide until

they come in contact with other cells• If you scrape away some cells, they will start

dividing again…• Most of the time, cells know

what to do and how to do it• But how…

10.3 Regulating the Cell Cycle

• Cyclins – a family of proteins that help regulate the cell cycle

• Internal regulatory proteins – proteins inside a cell– Make sure everything is timed properly– Cells don’t enter mitosis until AFTER DNA is replicated

• External regulatory proteins – respond to events outside a cell– Heal wounds; tell cells when to stop dividing– What if cells kept going and going and going…

Cell Death

• Cells are “born” in the cell cycle, and therefore must “die”• Happen by accident or injury, or…• Programmed to die = Apoptosis• Apoptosis is like self-destruction mode• Cell and DNA shrinks, parts break off, and neighboring cells

clean up the remains• Key role in embryonic development

Uncontrolled Cell Growth• If cells grow out of control, cancer results• Cancer – inability to control cell growth• Cancer cells do not respond to signals

that regulate most cells, and will divide out of control

• A mass of cancerous cells = Tumor• Benign tumors – do not spread• Malignant tumors – spread through

body

What causes cancer?

• Gene defects that regulate cell growth and division– Defect of gene called p53 is most common

• Smoking or chewing tobacco• Radiation exposure (X rays, UV rays)• Even viral infection• Common factor = can’t control cell cycle

Treatments for Cancer• Removal• Radiation – target a specific

area of the body• Chemotherapy – chemical

compound that kills cancer cells (it targets cells that grow rapidly, so it kills healthy cells sometimes too)– Serious side effects

• In which phase does the nuclear envelope break down?

• In which phase do chromosomes line up at the middle?

• In which phase is DNA replicated?

• In which phase are chomatids pulled apart?

• In which phase does the nuclear envelope reform?

• What is the final product?

During the videos, consider…• How is the cell cycle different in plants

compared to animal cells?

• How does cell division benefit us?

• How can the cell cycle cause us harm?

What is cancer, exactly?• Cancer is what occurs when the cell cycle gets

out of control and cells don’t die when they’re supposed to

• What causes cancer?• Can we cure cancer?

• http://www.youtube.com/watch?v=3kpR5RSJ7SA

• Does your cell cycle drawing match these descriptions?

• http://www.youtube.com/watch?v=Q9cuEYSt0GE&feature=related